at what point is gearing no longer helpful?

[Grantmac]

6:1 internal, it still uses the style of secondary reduction you are looking at.
Bafang Ultra is about half the power and won't pull a single speed like the CYC but fine if you want gears.

 

[Hummina Shadeeba]

I’m back to wanting to get a frame like this green one and using the freewheel cranks n going for the biggest gearing I can do with a belt n then the chain.


The other frame is just another I saw available.




This green frame has a hovering detached hub motor. But it has a single speed w a rear suspension that’s not hinging on the bottom bracket. Can you do that?

I’d just get the 90amp esc n the smaller motor and want to run a regular mountain bike parts. So this green frame is no good.

 

[thepronghorn]

I think that green frame will have pretty bad suspension characteristics from the chain tension pulling on the rear wheel. For minimal suspension effect, you want the chain to pass through the pivot point.

As far as when eddy current losses start to get unreasonable, user "thud" said 80xx motors didn't like spinning past 8k rpm or so. Most RC motor vendors do not list enough information to determine the breakdown between first order hysteresis losses and second order eddy current losses. The motor spreadsheet floating around in the motor technology part of the forum does have more information for motors that users here have measured.

 

[Hummina Shadeeba]

I think that green frame will have pretty bad suspension characteristics from the chain tension pulling on the rear wheel. For minimal suspension effect, you want the chain to pass through the pivot point.

Ok thanks you sound like you maybe know about what I’m looking for.

I’d like to get as many parts off the shelf as possible and ideal would be to find a rear swing arm for a mountain bike that I could attach and I’d get the front triangle made with an eccentric bottom bracket. You have any ideas on how i could make that work optimally? how bad would it be with the pivot point right behind the bottom bracket, or maybe it would be possible to somehow pivot around an an eccentric bottom bracket?


I won’t be pedaling this unless out of power and want to design the suspension for power.


The green thing was just a thought and like the design but unrealistic and I don’t want a 200lb bike. Thought it was a good price at 3600 shipped though.

Ill shoot for under 8000 motor rpm assuming 12 magnets and 14 poles. I’ll look for the thread.

 

[thepronghorn]

Why do you want an eccentric bottom bracket? Normally they are used to tension a chain on a hardtail, but it won't work on a full suspension bike unless the rear pivot is concentric with the motor or jackshaft which is very uncommon.

As far as the optimal frame design, I'm not sure about all your preferences, but I think it would be really cool to get one of the carbon ebike frames and build it up with a custom bottom bracket motor assembly.

There is also the boxxbike valkyrie which has a concentric pivot with both the BB and a motor. All of that stuff having to be next to each other makes for a really, really wide Q factor which makes pedaling not very comfortable.

 

[Hummina Shadeeba]

this made things a whole lot easier
. seems a not so bad price for then being able to use standard mountain bike rear wheel. https://www.youtube.com/watch?v=yWmxxeGn00A


or i could buy like 5 chainrings and fit them all on and see what fits and return the others. and replace my chain consistently. i like that more but fear it wouldnt work out well in the end.



“ All show.

I’m embarrassed to say that I did in fact own one of these nine foot long monstrosities.

But hey, it was the early 2000’s and everyone had a fat tired, fifty degree raked candy cane colored phallus in their garage.

It corners like an aircraft carrier.

It’s incredibly overpowered.

It’s woefully under braked.

With such an incredible rake, the front forks do not give you suspension travel… unless you’re running into a wall. The only suspension afforded is the flexing of the ridiculously long fork tubes and whatever tire pressure you can run in your rigid side walled low profile tires.

God help you if the roads are less than perfectly pristine. Mine was a rigid but even the Softail or dyna style rear suspensions were just as hard as my rigid.

The bikes road manners are less than forgiving. It’s not functional in the slightest. More like riding a sculpture of a motorcycle.

I don’t know how many Dickies pant legs were ultimately consumed by the 4” BDL open primary.

My 124” cubic inch motor and tiny little two gallon tank assured that the only thing I couldn’t pass was a gas station.

Long forks and incorrect triple tree/steering neck geometry result in an effect known as “chopper flop”. This is when, as you are transitioning the bars from left to right the front end picks up towards neutral center and flops down hard as you transition to left or right full lock. But like I said in the beginning, these bikes are all for show.” Quota.com

R I’ll just get a chain tensioner.

 

[Hummina Shadeeba]

getting this frame made.


and will just use the rear derailleur hanger with a pulley wheel to tension the chain and thats fine.


and will get a pulley brazed to the 19 tooth side of the double freewheel (17/19 tooth) to run a belt off the motor going to the cranks

 

[thepronghorn]

Why do you need a custom frame for this? What about a fixie frame with horizontal slotted dropouts for tensioning the chain? Not that I'm recommending you go 40mph on such a frame (neither a fixie frame nor the one pictured in your post).

Is it just to put the motor in the middle of the seat tube? It's going to limit your options for seat height adjustment. And look weird imo.

 

[Hummina Shadeeba]

I could get someone to braze the big tube into an old frame but the custom frame is pretty cheap at 540$ shipped and I’ll get rid of all the braze-ons that would be in the way of the battery too.




Horizontal dropouts would require a track hub which don't take big cogs. I’ve found a 49 tooth that goes on a standard mountain bike hub freehub body. https://www.nashbar.com/search?cID=&s=wolf+tooth+gc


And support part:
https://www.bikebarn.com/product/problem-solvers-singlespeed-cassette-cog-carrier-224573-1.htm?variations=1348929?utm_source=google%20shopping&utm_medium=organic&gclid=CjwKCAjw87SHBhBiEiwAukSeUWKey-C6czIPJ2W8uGUbBp7JBG6_r20-1WiS30d7HfK_QsUWA6wD3BoC-y4QAvD_BwE#.YO5AGiVHbYU

And hopefully the big cog doesn’t taco and I’ll make sure the chain line is good.

I can cut the seat post if I need to.



its not the sexiest but i can drill lots of holes in it. I'll have to drill some for the motor wires at least. It give more room for batteries and the motor is protected and im protected from it if it flies apart at 8k rpm.

 

[Hummina Shadeeba]

Why do you need a custom frame for this? What about a fixie frame with horizontal slotted dropouts for tensioning the chain? Not that I'm recommending you go 40mph on such a frame (neither a fixie frame nor the one pictured in your post).

Is it just to put the motor in the middle of the seat tube? It's going to limit your options for seat height adjustment. And look weird imo.

how far will my top speed on the road be compared to kv x volts x the wheel circumference? if i want to hit 38 max.





where's an easy to install hall sensor for a standard outrunner motor?

 

[markz]

How will they measure you to build the frame, and the riding position you want if its not in person doing the measuring because they have special gadget you sit on and they measure it all hence custom frame, $540 wouldnt cover the cost of measuring and building the frame.

Buy a frame thats close to what you want, make it a steel/cromo bike so you can weld stuff to it.

What size bolt do you want the braze-ons to be? M5, M6?
The more the merrier if you're hauling weight, doesnt take much to snap the bolts, done it a few times on rear racks with batteries. See these seem so weak, but if you got enough of them should be strong.
https://framebuildersupply.com/collections/braze-ons

Maybe a grade 8 bolt with these https://www.mcmaster.com/grade-8-bolts/high-strength-steel-coupling-nuts-grade-8/ if you can mount them, weld them on. Your probably not looking at weight savings are you :lol:
You could just buy a welder on sale from Harbor Freight then sell it after your done, if you go with a steel/cromo frame.
I watched video's on which welder to buy, its easier to learn on a stick arc welder then it is a mig and tig is the hardest.
Or look at the online classifieds for a buzz box arc welder old school Lincoln one, just make sure all the cables are there and clamps.

the custom frame is pretty cheap at 540$ shipped and I’ll get rid of all the braze-ons that would be in the way of the battery too.

 

[Hummina Shadeeba]

How will they measure you to build the frame, and the riding position you want if its not in person doing the measuring because they have special gadget you sit on and they measure it all hence custom frame, $540 wouldnt cover the cost of measuring and building the frame.

Buy a frame thats close to what you want, make it a steel/cromo bike so you can weld stuff to it.

What size bolt do you want the braze-ons to be? M5, M6?
The more the merrier if you're hauling weight, doesnt take much to snap the bolts, done it a few times on rear racks with batteries. See these seem so weak, but if you got enough of them should be strong.
https://framebuildersupply.com/collections/braze-ons

Maybe a grade 8 bolt with these https://www.mcmaster.com/grade-8-bolts/high-strength-steel-coupling-nuts-grade-8/ if you can mount them, weld them on. Your probably not looking at weight savings are you :lol:
You could just buy a welder on sale from Harbor Freight then sell it after your done, if you go with a steel/cromo frame.
I watched video's on which welder to buy, its easier to learn on a stick arc welder then it is a mig and tig is the hardest.
Or look at the online classifieds for a buzz box arc welder old school Lincoln one, just make sure all the cables are there and clamps.

the custom frame is pretty cheap at 540$ shipped and I’ll get rid of all the braze-ons that would be in the way of the battery too.

I was going to do that. A bunch of brazed on bolt holes in the frame I could mount stand offs and a plate but it just didn’t seem as simple and reliable as this. This seems a sure things and I get more room for batteries as well. And I’m serious in that I want to house the motor so if it comes apart on some rough ride it doesn’t hit me. I think will be doing 7000rpm which is within the stated specs but probably for a plane not a bumpy bike.

Brazing..seems an easier version of connecting than welding and I’ll have to do that to get the pulley to connect to the double freewheel. I have a friend who welds and might get him to do it. I almost got a frame building jig and was going to braze the whole thing but that’s getting out of hand snd like to finish this.



It’s a standard 18 or 17” mtn bike geometry. That’s fine. Fit isn’t that important. Right now I have an 18” frame and a 16” w raised stem and super long seat post. It’s not bad.


Will do the same type of battery as this


Got a fancy 50$ battery tester and it’s so fickle I’m returning it. Too hard to get a solid reading and if u move the contacts it changes.

Here’s a 16” bike I ride. I’ve had a 19” too and the custom frame is more so to get the mount on not get me fitted to the frame. “Fitting” is a hair from pseudoscience in my mind anyway after spending a life riding and having my road bike position change drastically over those years.


And a bunch of random related pics and u can post them here now


But what of my top speed in relation to it’s no load top speed? 35mph on the real road and 40 on the bench is my guess

 

[markz]

Seems like your doing a deep dive into a dream bike that handles well and good weight distro, otherwise I'd say why bother, just choose a bike, slap on a kit, figure out battery placement and have fun. I've read that some people who have purchased an expensive store bought ebike (Specialized) say the weight distro is damn good, but the biggest problem is proprietary components, wimpy weak power, speed limited, I'm guessing that pedal assist is mandatory though I never looked into it.


I do not know if brazing is as strong as welding. Then theres the vibrations and how that affects both types.

What does Mr. Spyware Google have to say?

Prowelding.com seems legit
https://prowelding.org/brazing-vs-welding/

Another official looking website
https://www.machinedesign.com/fastening-joining/article/21832464/when-brazing-beats-welding
This would sum it up

Both methods produce strong, permanent joints, so the obvious question is which is best for a given application. Let's look at several key considerations:

Assembly size. Welding is usually more suited for joining large assemblies. Brazing applies heat to a broad area, often the entire assembly. Larger assemblies tend to dissipate heat and can make it difficult to reach the flow point of the filler metal. Welding's intense localized heat overcomes this drawback, as does the ability to trace a joint.

Thickness. If both metal sections are relatively thick — say 0.5 in. or greater — either method works well. But thin sections tip the scales in favor of brazing. For instance, brazing is the better option on a T-joint with 0.005-in. sheet metal bonded to 0.5-in. stock. The intense heat of welding will likely burn through, or at least warp, the thin section. Brazing's broader heating and lower temperature joins the sections without distortion.

 

[Hummina Shadeeba]

Seems like your doing a deep dive into a dream bike that handles well and good weight distro, otherwise I'd say why bother, just choose a bike, slap on a kit, figure out battery placement and have fun. I've read that some people who have purchased an expensive store bought ebike (Specialized) say the weight distro is damn good, but the biggest problem is proprietary components, wimpy weak power, speed limited, I'm guessing that pedal assist is mandatory though I never looked into it.


I do not know if brazing is as strong as welding. Then theres the vibrations and how that affects both types.

What does Mr. Spyware Google have to say?

Prowelding.com seems legit
https://prowelding.org/brazing-vs-welding/

Another official looking website
https://www.machinedesign.com/fastening-joining/article/21832464/when-brazing-beats-welding
This would sum it up

Both methods produce strong, permanent joints, so the obvious question is which is best for a given application. Let's look at several key considerations:

Assembly size. Welding is usually more suited for joining large assemblies. Brazing applies heat to a broad area, often the entire assembly. Larger assemblies tend to dissipate heat and can make it difficult to reach the flow point of the filler metal. Welding's intense localized heat overcomes this drawback, as does the ability to trace a joint.

Thickness. If both metal sections are relatively thick — say 0.5 in. or greater — either method works well. But thin sections tip the scales in favor of brazing. For instance, brazing is the better option on a T-joint with 0.005-in. sheet metal bonded to 0.5-in. stock. The intense heat of welding will likely burn through, or at least warp, the thin section. Brazing's broader heating and lower temperature joins the sections without distortion.

I don’t see a kit that suits me. There’s nothing like I’m making around: mid-drive with a jackshaft using a belt then chain with the freewheeling cranks. I like building and I still believe this will be more efficient, way more powerful and faster, don’t forget cooler, and possibly a lot easier to service. The downside being this will sound like a hornet attack.

Just have to braze the pulley to this and the rear is standard stuff

 

[markz]

Building is fun, gives you a sense of accomplishment when its done and something you can smile at and you smile even larger when it works out good enough.

Like those who own classic cars, I often ask myself, is it bought or purchased. Of course one can't do it all like a grease monkey doing show room quality paint, or frame work (extension, shortening, straightening). Though you should watch some video's on Youtube, the East Indian people doing it all on dirt ground, dirt cheap labor with home made welders, zero power tools, spinning wrenches on tractor trailer rigs.
Now those people think outside the box because the have to.

 

[Hummina Shadeeba]

how thick you think I should make this plate and the tube? i was thinking just 2mm for the plate and 1mm thick for the tube. thats a guess. if you think it will fail please write soon!

 

[markz]

When will this project be completed?

Or is it a perpetual project?

 

[Hummina Shadeeba]

when they make the frame. the custom pulleys and all other parts are ordered as well. takes time and dont want to screw it up. a lot more expensive and time consuming than just adding a fat hub motor.

 

[Hummina Shadeeba]

I want to quiet the white industries freewheel. I don’t want to hear the ratchet at all really when I’m throttling. I’ve heard of using a thick grease but I want to do something more especially since I’ll almost never use the pawls by pedaling and the when I finally do pedal the big gearing will put little force into the pawls.

At 5min u can see the pawls.
https://m.youtube.com/watch?v=nkpv1WkbYrw&t=320s

What if I put the springs on a gas grill?

Paint some hard rubber on where the pawl slaps down?
Less pawls n springs?

Ideal would be to have no pawls and I’d bring them with me and add them when needed but that’s too awkward and would have to remove the crank arm.




But the related question:
I can change the motor from 100 to 200kv and it will go twice as fast, but with that 200kv is a decreased torque per amp vs the 100kv but it’s not the same 1:1 relationship, what is it? Why does gearing work in reducing copper losses?

 

[toolman2]

Yea, it is 1:1 for that part also. Ie double the KV is half the Nm per amp.
Copper (ir) losses are reduced heaps with gear ratio increase because motor torque is less for the same wheel torque.
Doubleing the reduction ratio halves the required motor torque and is four times less copper loss because it's actually I squared times r.
-double the motor torque is 4 times the loss, iron saturation and other things like ac losses/proximity effects make it even more loss and heating in reality when attempting to increase torque output at the motor.

 

[Hummina Shadeeba]

Doubleing the reduction ratio halves the required motor torque and is four times less copper loss because it's actually I squared times r.
-.

Comparing these:
100kv with therefore high torque per amp yet high resistance winding (4 ohm?)
No gearing
Needing 10 ft/lbs of torque
How much energy lost to winding heat?


400kv w low torque per amp and low resistance winding (1ohm?)
4:1 gear ratio
Need 10 ft/lbs of torque
“. “


4x less torque needed from the 400kv motor but will it need 4x the current, and will that winding be 4x as conductive?!

 

[toolman2]

Yea I got you, the 400kv and geared set-up would have 16 times less copper loss.

But a couple of things: the 400kv motor in this case would not need 4 times the current, it would actually be the same as the 100kv motor with no gearing. -the motor would make 4 times less torque from the same phase current but geared 4 to 1 brings us back to the same torque at the wheel.

And the if the 100kv motor was 4 ohms, then the 400kv one would not be 1 ohm but actually 0.25 ohms, 16 times less. -that part is squared too, so double the kv is 4 times less resistance.
The bit that remains the same though regardless of Kv is that both motors end up with the same amount of loss in Watts per Nm produced at the shaft.

Crazy to get your head around at first hey, but that's how it is and btw your right in your original questions and thinking I reckon, a LOT of losses, wasted battery power and heat are happening when folks crank a full size wheeled, hub motored bike to 10 or 20kw input. -you could hose them off the line with a kw or 2 into a half kilo motor when geared. :wink:

 

[Hummina Shadeeba]

:wink:

thanks for the thorough answer and i'll be reading it again im sure.


i had to get two sets of these steel pulleys made to get them to make them and wondering if anyone is interested in one pair. Uses GT2 12mm wide belt, 8mm pitch, which is really more than needed for the amount of torque I'll have on the first stage and could be used direct from motor to rear wheel and that torque. i forget what torque is appropriate for it actually at this point but its stout. think it was just over 400$ for both sets and shipping

the small one fits a locking bushing from fenner (could use different motor shaft sizes) which is nice and easy, and the big has an inner diameter to weld or braze onto a double freewheel

think they are 90 tooth and 22 or around there. forget that too.


how to balance the big pulley?




all n all the costs of the parts to do this mid-drive with 12:1 ratio and potential to still pedal..with custom frame, pulleys, locking bushing, double freewheel, belt, freewheeling cranks, motor.... i think worth it at maybe 1400$.

 

[LewTwo]

All of this reminds me of the "Kepler Friction Drive". He was using a small, high speed RC motor to directly drive the rear tire via friction. If memory serves that is about a 2 inch motor against a 26 inch tire ... effectively 13:1 ratio. Actually the rear tire just acted to transfer the movement of the motor to the ground. You have to spin a 2 inch diameter wheel fast (4250 RPM) to get up to 25 MPH. That was about 3 or 4 years ago and his goal was to reduce the weight as much as possible. I also seem to recall some comments made about the high pitched sound.

 

[Hummina Shadeeba]

With that friction drive the increased
gear ratio is nice but I imagine the friction drive is an inefficient gearing and I imagine the motor takes a beating too. If it’s that easy to get a big gear reduction while being efficient and not fall apart I’ll have wasted a lot of time.

It’ll be 3 months before the frame shows and I’ll post how it end up.


Will use this wheel and found these common mountain bike cogs can be drilled and adapted for single speed. It feels solid with lots of support.

I’ll also add a bolt under the bottom bracket shell to mount a common chain tensioner so it pulls against the small 17t “chainring” and don’t think can use the usual derailleur hanger as the 50t is so big


With a quick release rear end and only one cog I’ll be enjoying my flat tire changes.

But vs the friction drive..I’m trying to crush it in efficiency