Grinhill's Medium-power RC-Motor Hardtail build

[Grinhill]

Greetings all. The time has come to post some info on my efforts, although a lot of this build diary may be days or weeks after the fact.

Firstly a big thank you to contributors on this forum. I have to admit I haven't read all 83 pages of THE BIG THREAD that started all of this (about half of it anyway). I have been greatly inspired by numerous contributors such as Miles, recumpence, Erth64net, liveforphysics, scottclarke, Jason, john tetz. I think my build will end up most closely resembling Erth64net's build.

In this build I will be quoting costs in Aussie dollars (that's about US$0.65c at the moment), and metric measurements.

The first photo shows my previous e-bike, which I forgot to lock up in the yard at home one day and it unfortunately disappeared. The main downsides were not enough power and way too heavy - 20kg for bike plus another 12kg for hub motor and SLAs.

A year later, it was time to get a new bike, purchased 20-Jan-09. I did have motorising in mind when I bought it, although the plan wasn't clear. I wanted a mountain bike for its strength more than off-road capability, plus disc brakes for good stopping power. I have a commute to work of 6 km, mostly downhill, which would mean a hard ride home. I haven't ridden a bike to work for a couple of years now, hopefully that will change soon.

Where I live, it's not uncommon to have temperatures of 40 deg C in summer, and the coldest winter mornings are about 7 deg C (no snow!), so motor and ESC cooling will be an issue.

By "Medium" power I mean something a little more than Australia's 200W legal limit (...is that motor running???), but less than the 3+ kW builds (expensive and SCARY ).

My first plan was for a step up from my previous bike's 24V hub motor to a xlyte-408 or similar hub motor. I was looking at running it on 48V LiFePOs, which would probably have cost me around AU$1200 including batteries. I also looked at sy-clone kits, but decided I didn't want to mess with the cranks. After discovering the ES group, I have now decided to build something for similar price (less would be good) and power (approx 900W) but lighter and smaller.

Second photo shows new bike with a mock-up to see where things can fit.

 

[Grinhill]

Here's my quick specs:
- weight less than 4kg (8 pounds) including batteries
- power in the range of 600W to 1200W
- bolt on with no mods to the frame, no mods to cranks, no mods to hubs

Generally I will try and go with the lowest cost option that meets my specification, but I would be prepared to spend a bit more to simpllify installation or to look a little less obvious than dog's testicles.

Time for some research into what I need the machine to do - I investigated my commute to work using Google Earth and a spreadsheet. I broke the trip up into 100m increments and looked at the % gradient. The steepest section was 11%, and it was about 6 km each way.

I found swbluto's simulation software to be an excellent tool for this job. If I want to be able to ride up a 10% grade with about 200W rider input at sufficient speed to keep motor efficiency above say 60% (to reduce chance of overheating), I can then select the appropriate gearing to suit the Kv of my selected motor.

 

[voicecoils]

Looks like a cool project.

One massive one stage reduction is your plan?

What is your basis for deciding that you'll be able to provide 200W of mechanical human power up the hills? I'd like to know the mechanical power that I can output over various durations (burst, medium, long time etc) but I haven't been able to borrow a road bike equipped with a hub or crank mounted power meter (measured by strain gauge sensors).

 

[AussieJester]

WOOT another RC build and by a fellow Aussie wooohooo...AUSSIE AUSSIE AUSSIE hehehe

Bst of luck with the build mate shall follow with interest

KiM

 

[Grinhill]

One massive one stage reduction is your plan?

Yep, 17 tooth pulley driving Golden Eagle drive ring gives about 1:16.

What is your basis for deciding that you'll be able to provide 200W of mechanical human power up the hills?

OK, so that's a wild guess. I'm just not expecting to be able to sit back and be pushed up a hill without cooking the motor.

I've actually got all the gear, assembled it and been for two test rides so far, looking good.

First problem was the pulley wandering on the shaft, now sorted.

Second problem was the ESC losing sync. This happens quite suddenly, sounds like something breaking, but back off the throttle and gently ease it up and away it goes again. The present problem is that yesterday when this happened, a couple of the magnets also came astray with the shock. After the epoxy has set, it will be time for test ride no.3.

More details to follow soon.

 

[voicecoils]

cool so you are on the road with the bike then?

Do you have any photos of the bike with functioning drive? The one I saw in your first 2 posts was a cardboard mock up of the rear wheel. Might have missed it.

I wasn't having a go at you about the 200W rider input, just curious if you had some real data points for it as it's something I'm interested in finding out for myself.

ESC sync seems to be a common issue, liveforphysics is working through this as well.

Waiting for epoxy to cure is a PITA, I know the feeling of wanting to get out and test/ride. (Bastard little misbehaving hall sensors in my case :wink: )

 

[Grinhill]

So now for the components.

Motor - there is a spreadsheet listing most of the available RC Motors (link?) which was very handy. I was looking for something with small physical size (60 x 60), low cost, low Io, low Kv. Couldn't go past the offerings from HobbyKing. I went with a Turnigy 50-65 270Kv, from their black range which has supposedly better bearings and thinner laminations to make it more efficient. Power rating 2000W exceeds my requirements.

http://www.hobbycity.com/hobbycity/...TGY_AerodriveXp_SK_Series_50-65_270Kv_/_2100W

Voltage and Power - I decided on using 22.2 V (6S LiPo) as compromise on cost vs power for this build. This allows use of a cheaper ESC, which has a voltage limit of 25V.
http://www.hobbycity.com/hobbycity/...me=TURNIGY_Plush_80A_w/_UBEC_Speed_Controller

I will try and limit current to 60A to reduce overheating issues, and will probably add a Fechter circuit when it's sorted. Plugging these numbers into swbluto's simulator, this indicates that I can run this motor at around 900W input power in the speed range that I want (say 20 km/h to 40 km/h).

Batteries - It has to be some type of lithium chemistry to save weight, and I don't want to build my own packs. 20C current is more than enough. Drawing 50A from 5Ah is 10C, if I have two packs in parallel to get the required range, this would drop to 5C, which should be easy on the batteries. I've gone for HobbyKing again, in a 3S pack because it's slightly cheaper and gives me more mounting options.
http://www.hobbycity.com/hobbycity/...roduct_Name=ZIPPY_Flightmax_5000mAh_3S1P_20C_

Drive System - I was trying to avoid a crank drive, and mounting a multi-stage needs more space. My preferred options were a single-stage or friction. Tyre roller slips too easily, particularly in rain (based on experience of Zeta belt system). Whichever system was selected, a one-way bearing or freewheel was essential to allow easy pedalling. I thought through many ideas, like a "sandwich" system because it seemed to offer more positive grip, but mounting of second roller starts getting messy. The idea of attaching toothed belt to rim with epoxy sounded promising, particularly on my bike with disc brakes. Reviewing the HTD Bible shows belt would not be happy with curvature, plus only one or two teeth are in contact at any time. So it came down to the Golden Eagle pulley clipped on to the spokes with a single stage pulley, which is simple, proven, and reliable. Here are some tips from the ICE guys:
http://www.motoredbikes.com/showthread.php?t=4481

The only downside with this was the shipping cost to Australia, which ended up at $68, which they told me about after placing the order. :x

So at this stage my budget looks like being:
Bike $550 plus Parts $850 for a total of $1400 on the road.

 

[Grinhill]

vooicecoils:

Do you have any photos of the bike with functioning drive? The one I saw in your first 2 posts was a cardboard mock up of the rear wheel. Might have missed it.

sorry for the break in the space-time continuum...

here's a pic of the first assembly, needed to adjust motor mount to get belt tension correct.

Then here's the system at time of first test ride.

 

[recumpence]

According to my Eagle Tree, 200 watts is about right for sustained human output. I have tried riding at a specific speed and straight road, looking at the wattage output on my readout, then begin pedalling and see how much the wattage drops. 200 watts is about the average.

Matt

 

[Grinhill]

Here's some more of my build diary:

The belt must go on LHS to avoid the chain. I looked at 4 possible locations, the best seems to be the highest position. An idler pulley is not really required according to the HTD bible, but will increase wrap and assist belt path. It would be good to allow some adjustment in the motor mount for tension and angle. I decided to try it with no idler for my first attempt.

4th Feb 2009 - ordered Hobbyking parts (motor, ESC, LiPos, charger, wire & connectors) - arrived in about 3 days.

7th Feb 2009 - ordered Golden Eagle Drive ring. After some emails to sort out shipping, this arrived a few weeks later.

Ordered HTD belt and pulley and one-way bearing from Aussie firm Small Parts & Bearings, great web site, and they carry all the Gates belts and the SDP/SI stuff, took about a week to arrive.
http://www.smallparts.com.au/store/
I went with a glass reinforced polycarbonate 17 tooth pulley, mainly because it had a 20mm diameter section that I could easily bore out to 12mm to suit the one-way bearing. I also got a couple of small 8 x 12 roller bearings to take the radial load (motor shaft 8mm). In hindsight I should have gone with the wide drawn-cup version which already has the bearings built in, as it turned out that the one-way bearing was more than 12mm OD so I had to bodge the fitment into the pulley with epoxy. The belt length was 315 tooth (1575mm).

I then commenced fabricating the motor bracket from scraps of aluminium I found in the garage. This involved mainly hacksaw, drill press, hand files, bench grinder and emery paper. Later I also had to add some plastic spacers to get the belt tension correct. The bracket attaches to the V-brake posts with M10 bolts and a third bolt through the brace just above the tyre.

Here's the bracket:

 

[Miles]

What is your basis for deciding that you'll be able to provide 200W of mechanical human power up the hills?

For general values, see:
http://www.google.co.uk/books?id=0JJo6DlF9iMC&printsec=frontcover&dq=bicycling+science#PPA37,M1

Good to see your progress, Grinhill

 

[Grinhill]

Next step was a bit of work on the electrics. I only bought two of the 5Ah LiPos initially, and they seem to be out of stock now so I'll be sticking with 6S 1P for a while. My calcs for the Watt-hrs on the trip up the hill came in around 4.5 Ahr, so it is possible I could survive with just the two for a while anyway if I do plenty of pedalling.

I've used the right angle XT connectors throughout (deans copy). For the throttle, I had enough bits in my electronics junk box to knock up a single 555 timer circuit on a small board. I had to borrow a CRO to get the pulse width correct by adjusting resistor values, otherwise the ESC just beeps annoyingly. Turns out it it likes about 1.2ms for zero throttle, the motor just turns over at about 1.3ms, then by 1.8ms it's at full speed. I did the first bench motor test using one battery pack (11.1V). I'm using a 20K pot as the throttle but not using the full range of the pot, and I added a stopper to only allow movement in the required range.

After the first test ride I added additional capacitance (single 2200uF 35V cap) which you can see as a suspicious bulge in the heatshrink upstream of the ESC. I also added a heatsink to the ESC and re-wrapped it. I also added a de-spark circuit which comprises 270ohm and 180ohm 1W resistors in parallel giving 108ohm, activated by a small pushbutton below the main switch. This works well if you hold on for about 1 sec then flick the main switch on, higher resistor values wouldn't allow the ESC to start up. The main switch is only rated for 16A , but I am using two poles in parallel and not switching under load.

Here's the wiring loom after a bit of tarting up:

 

[lawsonuw]

Hows the drag from the roller clutch while off power?

Lawson

 

[Grinhill]

Hows the drag from the roller clutch while off power?

Initially it was not noticeable, the roller clutch just slid straight on and off the 8mm shaft. When I reassembled for yesterday's third test ride, I noticed that the "hardened" shaft has taken a beating and required some force to slide the bearing/pulley on. There was also additional noise when freewheeling probably due to the lumpy shaft.

I agree with Erth64net that this system probably won't be long lasting, and a sprag clutch arrangement would ultimately be preferable.

Another possibility would be to use a press fit hardened sleeve say 8mm to 12mm and use a larger roller bearing.

BTW my test ride went well, about 2 km, but the ESC losing sync problem hasn't gone away. I can't go above three-quarter throttle uphill. The pulley/belt system is brilliant, no slip even though there are only about 5 teeth engaged on the small pulley.

I ordered a Cycle Analyst yesterday, this will help monitor current to find the point at which I lose sync.

 

[etard]

This build is great. Have you tried two batteries hooked up yet? Have you added caps to the controller? Keep up the good work mate. What kind of speeds do you expect?

 

[Grinhill]

Thanks etard.

Yes I'm running 6S (22V) at the moment, with extra caps (no noticeable difference with caps, although if it preserves the controller it's worthwhile).

Theoretical top speed at 22V is about 44 km/hr, will let you know when I get the Cycle Analyst fitted.

I did wonder whether the larger 100A hobbycity ESC which liveforphysics was using would solve the sync problem for me since it wouldn't have to work as hard - it would still be half the price of a Castle .

 

[lawsonuw]

I also got a hobbycity controller for my experiments. I decided to get the "high dollar" controller. HexTronic Pro 120A with BEC (I got the USB dongle for it too) I have a hunch the BEC will work just fine up to the max voltage of the controller as long as it's only running a servo tester. I also added a lot of capacitors to the input as my experiments have ~4ft wires from controller to battery. This controller starts hard and has a funky throttle map, but seems solid otherwise. As I was driving the crank, I never had the motor accelerate me from a stop. But I did run my small motor well at very high loads once started. The best bet though is likely to skip strait to a Castle Creations Pheonex controller.

Lawson

 

[Grinhill]

My Cycle Analyst arrived, so I wired it up and took the opportunity to tidy up the rest of the wiring and make the throttle a bit more permanent.

I've mounted the throttle pot in a plastic container attached to an old bell mounting clamp, and I added a microswitch on the brake lever to break one of the pot wires ( it takes the ESC about a second to get upset and shut down). Some black paint to make it look a bit better. Also glued a thumb rest to the knob of the pot to make it a bit easier to adjust.

I also put the batteries in a drink bottle to look like it belongs.

Some notes on riding - the one-way bearing is holding up well, even running a bit smoother and quieter than it was. I can manage the ESC pretty well now, the throttle is very easy to nudge gently to stop it losing sync. The ESC doesn't get warm at all, adding the finned heatsink was probably unnecessary. The fan on the motor is definitely required as it does get quite warm after an uphill run.

Top speed is 44 km/h on the flat, and if I pedal as well I can maintain 35 km/h up a 10% grade, pulling 45A at 22V.

My longest ride so far is 7 km down the hill and back up, using 2.4 Ah of my 5 Ah battery pack, and everything worked really well.

Best of all, the total additional weight is not much over 2 kg including everything. Bike now weighs around the 18 kg mark.

 

[liveforphysics]

Your bike is awesome! Great work! I love with using an RC setup and LiPo, your entire added weight to the bike is only 5lbs! That's fantastic! I love the drive system too, I bet it's nice and quiet, and very light and compact. Very cool setup!

Best Wishes,
-Luke

 

[Miles]

Well thought out build, Grinhill. I like it.

If you rewound that motor to maximise the copper fill, it would run a lot cooler.

 

[Kurt]

Very nice, I like how you have kept every thing simple and used stranded mounting points on your frame. a 14 km range is good for the size battery.

Kurt.

 

[wanders]

Great project. I'm particularly interested in the spoke-mounted pulley from Golden Eagle. Does it compromise the wheels in any way? Looks a little scary to me...

What I'm waiting for is a BLDC controller (er, I forgot what sub-forum I'm in, I mean an ESC :wink that can also do regen braking, which is not usually needed or wanted in the RC world. Then, I would mount a similar motor without the freewheel and get braking as well.

Is the cogging torque in these motors high enough to really need a freewheel?

Again, great work! Fantastically light weight!

 

[Grinhill]

Thanks for all the positive feedback guys.

Great project. I'm particularly interested in the spoke-mounted pulley from Golden Eagle. Does it compromise the wheels in any way? Looks a little scary to me...

The wheel pulley works well, you can usually get them to within a millimetre of being centred. You really have to push hard on the spokes to get it click in place, and the spokes flex a little during the process, but it is solid when done. In my case, due to the frame design, I made the spoke slots deeper by drilling new holes 5mm further in, then hacksawed the slots deeper to reach the new holes. Even after this abuse, it still works well. I now have about 1mm clearance from the pulley to the frame, and the belt has about 1mm clearance to the tyre (after I sliced off the knobbys on one side). If you are lucky enough to avoid such additional work, all the better.

What I'm waiting for is a BLDC controller (er, I forgot what sub-forum I'm in, I mean an ESC :wink that can also do regen braking, which is not usually needed or wanted in the RC world.

These ESCs can be programmed to have braking, hard or soft, but this means that you wouldn't have the ability to easily coast down a hill, your motor would need to be driving any time you are moving.

Is the cogging torque in these motors high enough to really need a freewheel?

Yes, especially with this gear ratio. There is a noticeable difference if I turn the wheel backwards by hand.

 

[Grinhill]

I ordered a new ESC from hobbycity last week (a HV 100A unit) and spent some time this week wiring it up (had to find a 5V supply to power my throttle circuit since this one doesn't have a built-in supply).

It was all a bit of an anti-climax as I got no joy from it out of the box. No beeps, couldn't get the programming card to talk to it. There was no smoke, and it was drawing about 70 mA. Will have to contact hobbycity and send it back.

Anyone else had problems with these ESCs?

 

[Grinhill]

I've had a request via pm for a wiring diagram, so here it is. Sorry about the quality.