Mid monster/Hub monster powered cruiser in mind, seek advice

Hi fellas!

This is my first post here (passed maybe months reading before thinking of signing in). Could not find any presentation board yet it's not the main topic So...

Let's keep it quick, I'm a frenchie student, almost ending my course in civil law and tax studies. I'm into car stuff usually but got really interested in e bikes since this summer because I'm amazed at how some of you guys here build stuff. It's almost like building a zero emission motorcycle with the weight and lines of a bike (sort off). That's where the interest started from.

Back on topic! I can craft aluminum and steel, wood, heck I have possibilities. I want to build a custom cruiser. I already have design on paper but need a lot more reckon on best parts compatibility and also good compromise on the frame materials themselves.

The starting point is either get a rear hub monster from John in CR or its little bro mid monster. Reliable power, efficient and polyvalent.

The frame is designed to be for e bike, so there is plenty of room for battery packs and controller, even mid mounting monster can be fit. I initially thought of making the main frame in 6061 aluminium for example and put solid steel rear / torque arms with rear suspension and a dirt bike front fork. Either going for fat tires and rims or dirt bike wheels if the first ones aren't strong enough.

Most of you guys prefer to go the steel and chromoly way but this is heavy. The bike is supposed to support occasionnally 140kg weight (no I'm not that heavy, I'm designing a 2 seater for my wife). I try to counter the heavy load with lightweight materials (car dude's logic). I also see that there is a Hoboy carbon fork which is light and strong. A dirt bike fork has the advantage of offering true frontal suspension but is this really mandatory? I see downhill forks too, knowing how much power a well driven hub like John's can deliver I wonder if the dirt fork is overkill or needed.

I can craft a lot of materials but of course nothing like carbon, I let this to Drbass. What do you recommend? Lightweight and strenght are main words.

Mid driven hubs offer gearing use, plain hub are direct drive normally. Easy mount vs somewhat better weight distribution and range of efficiency for power. Not the main problem, both hubs are designed the same way but different size. The other problem is : for a mid mount, what gears/pinions/chains are strong enough to withstand the hub's strain?

Honestly I have no idea about what battery packs are worth for, only that 22s or 24s lipos packs will match my needs. What do you usually use at this capacity level?
How reliable is it in time?

About controllers, I was thinking of using 2 Sabvotons controllers for a good sinewave control, good choice or you recommend something else? I remember PAS can be done with it, it is important because in my country we fall under the 250w power limit.


Thanks by advance for reading me guys!

What top speed do you want, and what kind of hills do you have to climb? Range?

Subscribed cos I liked the ideas behind this build. Look forward to see this bike be hammered into shape.

Macribs --> Thanks for the interest !

John --> It's a pleasure to get you as first answer.
I did some measures on my way to work this morning, hills were ranging from 5 to 20 degrees. Range is not the main goal because I commute under 30km (including parking time when I search a spot), longer trips would be for cruising across the coast or the mountain (both are close or even melted together). Now if I can benefit bigger ranges by driving quietly, doing pedal assist or from good battery pack it's welcome.

About speed with rider only and flat ground I aim for 55-60 mph safe speed (means I'd like to get higher peak of speed but be able to ride at lower speeds with less stress on the bike) and with 2 people being able to ride at 15-20 mph.

i just my answers ready after i read your first post, but seeing your last one, and looking at the numbers you wish to achieve i think i can't contribute a lot.
first of all: yes. aluminium is the way to go if you can get the raw material. 6061 or 7020 or similar is not really something that you can buy around the corner. that (and the more complicated welding process of AL) is why many guys choose cromoly.
so you want to build a two seater that looks like 250w and 25km/h and is able to do 100km/h easily and can handle 20 degree (!! is guess you're talking about %, as 20° is ~35%) mountains/hills loaded with 2 ppl for 30km. that sounds like a LOT.
if i understand you correctly than this has VERY little to do with a bicycle. you are building an electrified motorcycle.
stopping a bike with 2 people from 100km/h needs REAL brakes. even though my 4 piston 203mm avid downhill brakes are really nice i would go for a motorcycle fork. which answers your question if you really need front suspension. i'm riding in the forest for 90% of the time and i can't imagine going w/o suspension, but even on a paved road 40km/h+ needs good suspension.
maybe you want to clarify your demand based on my assumptions and i'll be happy to give advise based on my builds.

Hi Izeman thank you for your detailed reply !

About the raw materials I have an easier access to Alu and steel than chrome moly, same for the machining I can put a "one single piece" frame.

My hills might not be at 35% (in another thread I saw a guy posting pictures of his location with 30%, it's way steeper than my location. The only places where I can go with such % climb are short hills or locations far away from home where another transport shall be needed. I did measure in degrees while moving though.

The visual aspect is custom, this thing doesn't look like a regular bike at all on primary design and it's alright , my local police is not bothersome with exotic stuff. They only pull you over when you don't wear helmet for example or have bad driving behaviour. Yet the PAS for me is needed just to limit power on the go if I'm pulled over for a check. Anything more power than 250w is considered motorcycle and need proper insurance plate licence etc. It's a safety feature for me. The point is that even with "big visible stuff " like the hub and batteries encasing, they won't bother me as long as I don't overdo it. That's why I aim for high peak and hopefully decent torque. I'm thinking more and more about mid drive to get variable gear ratios and help the motor (I remember reading that some motors prefer high revving ranges than low revving, thus revving it higher with small pinion might help torque and reduce stress in climb, please correct me if I'm wrong).

I'll post a sketch shortly, just to give you an idea. I had a bobber, batman, cross fat bike and Phat Stretch limo as inspirations sources.plus I'm almost 2 meters tall so the thing is big.

As far as power use go, it will be either going at a slow pace with my wife on the back, just chilling and cruising or taking her home (torque and gearing will help). I'd have more fun only when alone riding the bike. The total range is the less important part because I'm sure to reduce total distance just by reducing the searching of parking spot at work. But guys here with monster bikes have more range than 30km and I aim way under the top tier, should be OK if I manage ideal power to weight ratio (adding my own legs power to haha).

I'll take your advice and go for the motorcycle fork, braking is also important but I don't have searched yet, any advice is welcome too!

By the way your Kona and your Klein are awesome builds ! How did you set the rear suspension in the Kona ? Spring load etc? How much does it weight ?

Vanarian said:

By the way your Kona and your Klein are awesome builds ! How did you set the rear suspension in the Kona ? Spring load etc? How much does it weight ?

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thanks kona is 34kg over all with 1kwh of lipo. which is about double the weight it had before conversion. rear spring is still an issue and maybe a tad too soft but i like a smooth ride and it don't do real freeride stuff like 5m jumps. i have downhill colleagues at my office who gave me different springs to test but i kept the original one which i liked best.

please post a sketch as atm i have no idea what this could look like. i have a picture of peter fonda harley in my mind
i have not seen one mid drive with bicycle chains and gears on the rear hub that can do 100km/h. for 100km/h you need 10kw+ (even more if you are like the two of us - just under 2m) and even more if you are 2 ppl on the bike.
i could not recommend or imagine any bike chain or cassette ratchet that will withstand this force for a longer period.

60mph is a piece of cake, adding the hills is the main concern. How long are the steepest sections, and what kind of grade is in front of it. I ask because my 60mph cargo bike has been up some incredibly steep sections 30%+ grade, but I was able to attack them carrying good speed into the hill. OTOH my cargo bike can't handle much greater than 10% continuous. Don't worry, it's just running a stock hubbie less capable than a lot of the bigger hubmotors guys are running, and nothing near the capacity of even MidMonster, especially out of wheel. I bring it up to highlight the difference between a steep hill and a continuous climb. Two last questions though, will your wife be aboard during the steep climbs, and are the road conditions of those hills good, so curves or poor road would prevent a 30-40mph ascent? I ask because a big load up a climb is a different animal than you solo, as is being forced to very low speeds during climbs. It's important because bigger loads obviously require more power for climbing, and something to keep in mind that all of our systems are able to produce their maximum power at an rpm slightly below our top speed on the flats.

Regardless of the answers to the remaining questions, I think MidMonster is a better choice due to the weight and space savings, and the all aluminum shell makes it more easily modded for a mid-drive installation. It's ultimately capable of a bit less power than HubMonster, but in a mid-drive setup you'll be able to volt up and gear down to keep the motor free of stress. If you planned in-wheel use, then HubMonster would be the clear choice.

A pair of Sabvotons running relatively stress free will be up to the task, since field weakening can ensure the top speed while gearing relatively low for the hills. You may want to wait until I have results with the higher voltage controllers I'm about to begin testing on a MidMonster. They will be significantly cheaper, but give you a higher performance rig due to higher voltage and lower gearing. Bluefang is running a pair of Sabvotons on his HubMonster with significantly less heat, so we know that setup works well with the 6 phase dual controller alignment.

I don't know how far along you are with actual build plans, but you will need to plan for ducting for air intake into your housing as well as the exhaust flow out to the rear. With the cooling strategy I'll lay out for you the motor will be able to create all the flow you'll need and that will include airflow over the controllers to keep them cool, so you can hide everything if you want. Don't underestimate the rigidity and strength needed between the motor and wheel axle, because you're probably looking at 15-20kw motor input and serious torque that goes with it. Unless your roads are very smooth you'll need rear suspension, and my suggestion would be to put the motor axle in the swingarm pivot or on the swingarm as close to the pivot as practical. I'll go over the rationale behind that in a later post. For road use you won't want a lot of suspension travel, so keep that in mind for fork selection and rear suspension design.

Your gearing reduction will be relatively small, but the size of the disc brake mount on the motor will mean a drive pulley or sprocket diameter that is much larger than on a motorcycle, but the extra leverage of the larger pulleys or sprockets means smaller belts or chain is needed. It also means less noise. I have some pulley stock for Gates Poly Chain belt drives, and a 12mm wide belt will be plenty strong, and since you have the metal working capacity that would be my choice for a near zero maintenance solution.

It sounds like a great project, and I'm glad you asked about it publicly, so people can appreciate the planning process that goes into this type of rig.

John

ps- I just stripped most of the thick aluminum off of the magnet backing ring on the MidMonster I'm working on, and as soon as I verify that I didn't cause the motor to be out of balance in doing so, I'll share some pics soon.

John in CR said:

...60mph is a piece of cake...

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sorry, but you make my post look like BS. sure you can do 100km/h on a bike. that was out of question. but the TS asked for gearing and hub/chain recommendations. and this imho is not possible to do.
so we may agree that speed question is answered and only hub motors remain, but this won't go together with bike and riders weight for hills. i'm still unsure if vanarian wants to shift gears or is only talking about reduction (or single gearing). first one is imho impossible for this power demand and second can easily be done with kart chain or a belt. for me personally middrive always goes together with shifting so therefore i don't see the benefit of middrive over a hubmotor if you remove the gears. only advantage that remains is reducing the unsprung wait.

izeman said:

John in CR said:

...60mph is a piece of cake...

Click to expand...

sorry, but you make my post look like BS. sure you can do 100km/h on a bike. that was out of question. but the TS asked for gearing and hub/chain recommendations. and this imho is not possible to do.
so we may agree that speed question is answered and only hub motors remain, but this won't go together with bike and riders weight for hills. i'm still unsure if vanarian wants to shift gears or is only talking about reduction (or single gearing). first one is imho impossible for this power demand and second can easily be done with kart chain or a belt. for me personally middrive always goes together with shifting so therefore i don't see the benefit of middrive over a hubmotor if you remove the gears. only advantage that remains is reducing the unsprung wait.

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The advantage of taking these motors out of the wheel is huge. That's because the low pole count, high quality stator steel, and overall design make them capable of well over 2krpm without significant iron losses (which increase with operating frequency) kicking in. All direct drive hubmotors are geared too steeply with the wheel size they run, and in every case the smaller the wheel the less stress is put on the motor. The result is greater acceleration and greater efficiency by using a smaller wheel. Depending on the voltage Vanarian decides to run (the higher the better), I expect that he'll end up with a fixed gearing that would be the same as running the motor as a hub motor in a 12"-15" diameter wheel.

The answers to the questions in my previous post are needed before making any firm recommendations, but here's why running the highest practical voltage is best. Power = torque X rpm. The torque comes from current and the relationship is fixed by the motor constants until you reach saturation where you get less and less additional torque for each increase in current until you reach full saturation where the stator steel can make no more magnetic flux. RPM is determined by voltage and also has a fixed relationship. While we can easily increase power either way, heat is our overriding limitation, and the overwhelming majority of heat in our motors comes from resistance in the copper. Iron losses are quite low and increase mostly linearly with rpm. Copper losses, however, increase with the square of current. This should be a sobering concept to any DIY ebiker.

For example let's say you're running 60V with 50A max current. Let's assume no-load current is 2.5A at that voltage, and since current is negligible we'll ignore the copper loss component, so the 150W (60V x 2.5a) is the iron losses. Let's further assume that your setup is reasonably good, so at peak power the motor is at 75% efficiency (power out is 2250W), and peak power occurs at 2/3rds of no load rpm, so iron losses are only 100W at peak power. That means at peak power the heat from copper resistance is 650W plus 100W from the iron, so 750W of heat, a manageable amount but near the maximum heat dissipation of most stock hubmotors.

First, let's double the power input by increasing max current to 100A. The copper loss will increase by 2 squared, or 4 times, so copper loss at your new peak power goes to 2600W, and because only torque increased, the iron losses stay at 100W. Now you have 2700W of heat for 6000W input, so only 55% efficiency and you now have 3300W of power output, so you increased power input by 3000W for only 1050W more output.

Now, let's double the original power input by doubling the voltage to 120V instead. We'll also reduce the gearing by half so wheel rpm is the same. Copper loss stays the same because we haven't increased current, and iron losses double due to double the rpm, so they're now 200w. Add the 650W of copper loss for 850W total, so we're still inputting 6000W, but getting 5150W power out for 86% efficiency due to the less stressed motor with lower gearing. It's the same torque at the wheel with drastically different results.

That's the advantage of running a hubmotor out of the wheel and why increasing voltage and decreasing gearing (volt up and gear down) is by far the better way to go. While the above was just a ballpark comparison and there may be some other minor heat increases when doubling rpm, the assumptions are pretty realistic. Why not do the same with a non-hub motor instead? You can, but normal operation already puts them at the high end or their rpm limits, so iron losses are already a much higher % of total heat, and the small drive sprockets and high rpm means more noise along harder to achieve gearing reductions. Why not use a common hubmotor? You can, but their lower efficiency and higher no-load current means higher iron losses to start, and the high pole count brings rpm limitations into play quickly.

For the power I think Vanarian will need it will require higher current levels, so I'd recommend simple cooling mods that are working great on my HubMonster driven bike which has the motor in a 19.25" wheel pushing 27kw peak into the motor at 111V nominal. MidMonster is only about 20% less motor than HubMonster, and he will be geared lower (mine is geared for almost 120mph no-load) and he'll be pushing a lighter load during high performance riding, so MidMonster will be plenty of motor for him and still run it at low stress for absolute reliability.

Regarding variable gearing, a sufficiently powered electric vehicle needs no variable gearing for the kind of duty Vanarian plans unless it includes long very steep or slow mountain ascents with his wife on the back. No derailleur or internally geared hub could withstand the torque of this system anyway. Heavy duty bike chain may actually work though since he'll need a 22-25t drive sprocket to fit the motor's brake disc mount, and the readily available sprocket sizes, may make it worth going that route for testing and determining exactly the gear ratio he wants to run. The pedal chain line would either need to be completely separate, or use the motor as a jackshaft.

John

Lot of points to answer to, I'll try my best!

First of all here is a sketch made quickly from my phone :


I didn't have time to make other views, purple rounds were just an image about how the thing could look with two direct drive hubs (plus easier to make frame bars visible on drawing) please don't mind them. Eventually you can also imagine them as brakes. I'll post upper view later, the bike is not flat. I plan to solder a Yamaha rear plate behind the seats so either a bag fixation or a supplementary battery pack area possible too. Front low area with holes is where controllers will be put, to get frontal fresh air (Front Mount Intercooler logic, car dude is hitting again). Upper and central areas can be filled with battery packs. Lower center and rear areas can then be totally allowed to mechanic parts. I plan to duct holes in the battery area with protective grills to refresh them a bit too. Tell me if something must be switched or improved, I can redraw easily.

Tell me if I'm right (trying to assimilate everything) : a single fixed low gear provide better acceleration but field weakening can allow top speed while reducing total stress on motors, hence reducing heat and power loss? A full "cassette" provides the benefits from a gearbox (demultiplication ratios) but for bike sized components there is not a single one strong enough to withstand the torque? Or cassettes are ok and the faulty parts are shifter/clutch (don't know the exact name) and derailleur? Can't I try and craft a stronger part with heavy duty materials?

For the use, my wife would ride on the back with me but only on short hills I think. On commuting route the longest one is 1km I think, usual ones range from 100 to 300-400 meters. The worst climbs are exit routes to leave the city, definitely you have few kilometers before reaching the top. Plus these roads are a bit on the curvy side. My daily commuting routes are essentially straight lines with possibility to get at least 50 meters of flat ground to accelerate Maybe for real trips I would plan a seperate bike build for her, but heh let's see what can be done for this one already !

looks nice. w/o going into detail: the seat post WILL break if you do it like that. even with oversized tubes you would need some support. it can work with one person, but a second person sitting around a meter away from the welding point no way ...
as john confirmed: forget shifting, get a powerful enough middrive and install a strong chain and freewheel. this can be a very nice ride. if you want trouble free batteries go for 18650 cells or a123 or something similar. if you can buy nissan leaf cells - they are nice too.

You want to volt up and gear down as much as practical, because it's the best route to the power you need. As I understand, if going the sine wave controller route that field weakening has little cost to extend the rpm range higher, so it's a bit like running a higher voltage, though it will have reduced acceleration at the top end of the speed range compared to simply running a higher voltage. You also don't get the heat reduction advantage of using higher voltage that I explained in the previous post. The motor is a pretty easy load for controllers, so you can run it up near the top end of the controller voltage limits if you end up going with 100V max limit controllers. It won't be as good as going with say a 30s or 32s battery pack, so you'll give up some overall efficiency and passing acceleration. It's worth the short wait to see my results running 30S (111V nominal), with only 80A peak battery side and probably only 120-150A phase current limits (per controller). These controllers have economy and boost switches for cutting back or boosting current limits by 20% on the fly, and much better throttle tuning than common controllers including 2 different tunable settings to switch between on the fly, giving you the ability to switch to a soft easy launch with the wife aboard or in slippery road conditions. They're even programmable with a smart phone, and the best part is they're under $400 for a pair, which is unheard of for a motor control system that can take you well above 20kw input.

You won't need nearly that power, but if you run high voltage, you may be able to dial current low enough that the motor doesn't even need ventilation. With your light load you will probably have trouble even getting the motor to draw max current except accelerating on hills, so riding in economy mode may be pretty extreme performance for normal riding. Then when a sports car or a regular motorcycle pulls up next to you, you can switch over to boost and flat out embarrass them up to about 50mph where your acceleration has tapered off enough that they start catching up.

Regarding multiple gears:
Imagine if a gasoline engine had such a broad torque range that it could have good acceleration from a stoplight and run up to highway speeds all in the same gear. That's essentially what an electric motor does for you. The Tesla's have a single gear, and so do train locomotives which are a diesel motor generating electricity to run a single gear electric motor. Variable gearing for electrics is only needed for underpowered systems, and with each increase in gear torque is chopped down, so acceleration sucks more and more. Brammo put a gearbox on their moto (not their race moto though), but it's really just a marketing ploy to give buyers something familiar, and riders typically just ride around in one gear. You really do only need a single fixed gearing, and that means you retain regen braking too.

BTW, I love the design, low and sleek, which is great for speed. Definitely front load the battery weight as much as possible, because front traction is the primary handling issue with weight so far to the rear with a long wheelbase and raked back forks. Be especially careful with the front brake in slippery conditions, because that's the only thing that's put me on the ground, always really low speed stuff. A speed with a healthy 3-4" trail they track beautifully like being on rails.

Vanarian,

I remeasured the MidMonsters as having a Kv of 14.36rpm/volt instead of the 16 I was thinking, so it will be a bit more important to run at high voltage than I initially thought, at least for those wanting to push them to high power. That's because the thinner longer copper to wind to the lower Kv means they will have less current handling than I was expecting. That will make them an even easier load for controllers, so I'm going to go to 32s lipo with mine. I may still go to 100A per controller, but it will require ventilation at that current level, so first I'll try them at 75A+75A and see if I can get away with keeping the motor sealed. It definitely means my plans to push well past 20kw input are in doubt, at least until controllers with 200V components become available. Oh well, I guess I was being too greedy in terms of power at this price point and motor rated just 3kw by the manufacturer.

John

The attached bike is a mini-monster powered cruiser running a chain drive. It has pit bike front suspension for the braking advantage = better sheer stopping power then the best bicycle brakes for ~$100 for the lot rather then a few thousand. If you want ok quality forks at a reasonable price look for Fast ace forks. This bike comfortably does 80km/h, runs at peaks of 14kw and the 80km/h takes ~4kw and so far i have not been able to get the motor more then warm(can easily hold your hand on it). It is vented properly, not stupid random holes, and also running on 32S20AH batterys so its a long range cruiser. It also has large pegs on the back for a second person to go for joy rides. Handles that with ease even going up retarded steep roads.



A mid-monster will be more then enough. I am currently building a composite framed light dirt bike that will be using a vented Mid-monster with a pair of Max-E controllers to produce peaks of 30kw on 22S. I would now use a pair of Golden motor controllers at a higher voltage or even Sabvotons but i bought the Max-E before they were readily available.

Bluefang said:

The attached bike is a mini-monster powered cruiser running a chain drive. It has pit bike front suspension for the braking advantage = better sheer stopping power then the best bicycle brakes for ~$100 for the lot rather then a few thousand. If you want ok quality forks at a reasonable price look for Fast ace forks. This bike comfortably does 80km/h, runs at peaks of 14kw and the 80km/h takes ~4kw and so far i have not been able to get the motor more then warm(can easily hold your hand on it). It is vented properly, not stupid random holes, and also running on 32S20AH batterys so its a long range cruiser. It also has large pegs on the back for a second person to go for joy rides. Handles that with ease even going up retarded steep roads.



A mid-monster will be more then enough. I am currently building a composite framed light dirt bike that will be using a vented Mid-monster with a pair of Max-E controllers to produce peaks of 30kw on 22S. I would now use a pair of Golden motor controllers at a higher voltage or even Sabvotons but i bought the Max-E before they were readily available.

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Bluefang,

It's great to see that your Green Cheetah back on the road. You definitely lead the way by taking one our motors out of the wheel to run as a mid-drive. They're so under utilized in terms of rpm even at 120V, that we'll never be able to unleash their real potential until we can get controllers that can handle 200V fresh off the charger. I just wish I could get you off of the idea of pushing them to high current due to the huge hit to efficiency. This lightbulb really only clicked on for me recently, and the example from my earlier typically long winded post bears repeating.

Copper losses increase with the square of current. This should be a sobering concept to any DIY ebiker.

For example let's say you're running 60V with 50A max current. Let's assume no-load current is 2.5A at that voltage, and since current is negligible we'll ignore the copper loss component, so the 150W (60V x 2.5a) is the iron losses. Let's further assume that your setup is reasonably good, so at peak power the motor is at 75% efficiency (power out is 2250W), and peak power occurs at 2/3rds of no load rpm, so iron losses are only 100W at peak power. That means at peak power the heat from copper resistance is 650W plus 100W from the iron, so 750W of heat, a manageable amount but near the maximum continuous heat dissipation of most stock sealed hubmotors.

First, let's double the power input by increasing max current to 100A. The copper loss will increase by 2 squared, or 4 times, so copper loss at your new peak power goes to 2600W, and because only torque increased, the iron losses stay at 100W. Now you have 2700W of heat for 6000W input, so only 55% efficiency and you now have 3300W of power output, so you increased power input by 3000W for only 1050W more output.

Now, let's double the original power input by doubling the voltage to 120V instead. We'll also reduce the gearing by half so wheel rpm is the same. Copper loss stays the same because we haven't increased current, and iron losses double due to double the rpm, so they're now 200w. Add the 650W of copper loss for 850W total, so we're still inputting 6000W, but getting 5150W power out for 86% efficiency due to the less stressed motor with lower gearing. It's the same torque at the wheel with drastically different results.

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Volting up and gearing down with a motor that can handle much higher voltage is definitely king.

John

Izeman You're totally right I need to redesign the seat supports. I need too to check these Leaf Cells, I don't know what it's worth for and I see lots of good review on it. I'll re-sketch it by taking the seat support in account and also the frontal weight as John said, incoming shortly!


John You say out of the window but I'm sure it's a matter of time before you pull the right string :wink: Anyway even with under use of the hub's true efficiency range (just got to see your last post too), it will already be plenty of a monster for me. When the time comes I shall follow the lead haha.
I'll wait for your results with the current tests, it's alright! I trust you guys with batteries, you definitely have more knowledge than me.


Bluefang Your cheetah is wonderful, how much range do you achieve when you run it at a "slow" pace? Is it easily manoeuvrable? Are you sure pit bike fork can be enough for the load and speed? It is surely more affordable but I'm afraid of breaks or wild shakes.
By the way you have an interesting mid-mount location. The hub doesn't weight too much in overall balance?


I may add more of a "sportbike" logic to the overall design, still low but more frontal agressive maybe. I'm just afraid of flipping over with a hard brake, had bad experiences before with regular bikes :lol: of course the weight won't be the same but still. I'll need to check how to get a progressive yet strong braking. Active regen can also be good. I also fear the overall sitting position might be less comfortable, I don't know.

I got wild ideas running in my mind, if I take in account everything you've written till now, upper voltage, bigger batteries, lower gear ratios plus field weakening can give a good combos is it alright? I trust Brammo also if they don't have a gearbox, still my head is itching : you are 100% definitive I can't get any benefits from a custom gearbox? I'm even thinking of making a mini 2-speed Lenco type gearbox with the 1st gear as the main gear for everything, and 2nd gear for extra top speed when the 1st one is topped out. 2 mini levers would look pretty cool by the way, but if it is 100% useless I won't bother.

John in CR said:

Bluefang,

It's great to see that your Green Cheetah back on the road. You definitely lead the way by taking one our motors out of the wheel to run as a mid-drive. They're so under utilized in terms of rpm even at 120V, that we'll never be able to unleash their real potential until we can get controllers that can handle 200V fresh off the charger. I just wish I could get you off of the idea of pushing them to high current due to the huge hit to efficiency. This lightbulb really only clicked on for me recently, and the example from my earlier typically long winded post bears repeating.

Volting up and gearing down with a motor that can handle much higher voltage is definitely king.

John

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Would it be possible to have manufacturer change/increase KV for those motors? That way it might be possible to get more without going 200V?

Vanarian,

The CA I was using yesterday was acting up, so I swapped in another today to get no load current, and I realized I had the wrong pole count. The correct Kv is 14.36rpm/volt, which is higher than the older 12rpm/v MidMonsters I have with rims cut off in Baton Rouge. That puts 20kw+ at 120V plus back on the table while retaining high efficiency. The strand count on the windings is 12, but that's for 6 phases, and the equivalent of 24 strands for a 3 phase motor such as the MXUS3000 in current discussion. I have little doubt that with my cooling mods I can push them at 100A per controller, though as previously discussed lower current is more efficient.

Something I had not measured before was no load current, and at 1695rpm on 118V, the no load current was 2A reported by both my .25mOhm shunt + CA3 and confirmed by the analog amp meter I was using. Except maybe HubMonster, which I've never measured without a rim and tire, there's no hubmotor on the market for under $10k (the CSIRO motor used for solar challenge competitions now costs in excess of $12k) that even comes close to as low a no-load current at high rpm. Common hubbies will have several times that no-load current at lower rpm. Assuming copper and bearing losses are negligible, that puts MidMonster's iron losses at just 236W at 1695rpm, which is irrefutable evidence of MidMonster's very high efficiency. I bring that up because several on the forum have dismissed our motors as too good to be true. Hauling a fat guy like me at extreme performance without melting down in a mountainous area was proof enough for me, so I didn't really care. Let them play with motors made for remote control toys and hubmotors pushed into saturation for under 10kw at the wheel, which kills their riding time. Considering the weight premium and the bigger premium, space why buy and carry battery energy only to turn it into heat in a big heavy wheel? Move that weight forward to the swingarm pivot, and reduce the waste heat through higher voltage, lower current, and gearing reduction for the same power input and torque at the wheel, but greater power through increased efficiency. These motor have a compact OD, under 200mm at the center depending how thick and aluminum fin you retain after cutting the rim off. A scratch build with feet forward cranks allows this easily without the width being a problem. Passenger foot pegs would be good there too, so you get a single area of strength in the frame serving many uses, which is the path to best power to weight. Power to weight and efficiency our ultimate measures.

You're much lighter so you will require significantly less power than I to achieve extreme performance. 10-15kw input on your bike will be like 15-20kw input on mine. The decreased load will give you better overall efficiency than my bikes due to reduced work required during acceleration, so even lower currents. I do stand by the recommendation that you run voltage as high as practical for greater efficiency and to reduce the need for ventilated cooling, which will depend on riding style, speeds, distances, and terrain. One thing is sure, and that is running a higher voltage will mean running lower current and current is what makes heat. When you can reduce gearing, increasing voltage can be relatively free of losses, so you come out way ahead by reducing current for the same power with that motor.

The higher voltage is inherently more dangerous, so due care and best practices is required.

John

That's good news, even better overall power from the hub then I trust your hubs, for having seen some threads here with your units you can't be wrong. I prefer "overengineering" than "underengineering", a stronger unit gives you room to make upgrades or even allow to forgive mistakes. You got very promising results with your hubmonster, correct me if I'm wrong (I'll search again the thread) but your son does ride a direct drive mounted mid monster, isn't he? He's still achieving pretty impressive results too with his bike. That's plenty of value for me.

Still I'll need guidance afterwards to set the right amount of current/voltage/amperage!

Here is a second iteration, trying to strenghten design and move forward mass of the bike. Got something wrong with the rear seat, it should be fixed only at the end of the tubes. On this version batteries could be packed close to the controller; controller in full frontal or upfront, and batteries close to it in a "7" look-a-like assembly. I was thinking of flat pannels to cover the whole components, with multiples holes in the front for cooling, a bit of aero and also protection (random rocks on the road or unlucky falls) and bigger opening in the back to allow air and heat evacuation.



Another question, If I'm guessing correct, ventilating the hub makes it cooler but also exposed to dust and water? (I recall seeing a Hubmonster with drilled holes in the hub housing) Do you know of a way to prevent exposure ?

The only way I can think of to avoid exposure for your hubbie would be not to drill it in the first place. If you need cooling you might wanna look into water colling with a pump and a radiator. You can get ie mxus 3000 or is it gt 4000 with water cooling from Linukas. That would take care of your heating issues as well as keep you hub internal safe from exposure to water, dirt, sand and shit.

If you end up going ventilated, it will be quite simple to cover it with a housing or just shielding than will deflect, block, and/or filter debris that will also help increase flow rate. I used to worry about stuff getting in the motor, but with all the vented motors on the forum there haven't been failures. Mars and Etek motors are open to the elements. Look at car alternators too.

With voltage high and current low I think you should try it sealed first, and increase the surface area for better cooling by cutting heat sink fins into the thick aluminum shell. I ran my Hubmonster in stock form at 225A peak battery current at 74V nominal with the motor in-wheel and geared for a 107kph top speed pushing a total load of 185kg for 9 months without severe heat. Sure it got well heated on long generally uphill rides, especially when I showed off more than usual, but nothing like other guys push their stator temps. Venting will be easily done later if necessary, and if so only very small grit could possibly enter and what does manage to get in will flow right back out of the exhaust.

Got asked in a PM for more info on the Green bike. There is a build thread here https://www.endless-sphere.com/forums/viewtopic.php?f=28&t=45165&start=100

It was a cheap and easy build so no fancy detail work, just hacked off the rim flange with a grinder, with the mid monster its just a bolt on sprocket setup using 219 chain. Fyi for 219 chain you can find alot of cam shaft sprockets for cars that are 219 chain and are around 30t which makes it easy to do a 2-1 or 3-1 gearing setup. With regards to cooling holes sucking up debrise, the motors spinning so fast nothing larger then sand could get in, but i have been running a mini monster vented like that for ~3 yrs with no ill effect.

Using a hub motor in a mid drive you have to mount the shafts to the frame and attach a sprocket to the motor shell, in Midmonsters case there is a nice disc brake mount that could be used. With mounting the motor i would suggest something solid to hold each side but the main thing you need is a tensioning bar on the drive side mount of the motor to the drive side of the wheel, assuming you cannot keep the motor mounted along the swing arm.

Have a look at my facebook page ausEmoto for more photos that show the motor mounts abit better. And the motorbike with the air cooled hub thats not having a problem ingesting anything even tho its super close to the road and is ridden rain, hail or shine atm.

John, you have never had to convince me about high voltage been the best option Only issue is there were no sine wave high voltage contorllers when i bought the Max-e ones. My brother is thankfully super close to getting the IGBT IPM Lebowski controllers up and running.