Commuter Booster - <1kg Friction Drive

The BrainBox measures the battery current & voltage. Calculates the power, then uses this in a PID loop to set the throttle signal to the ESC.
The enforced power limits are way lower than what the motors are able to deliver unrestricted.

As for an engage switch. If I had to go to that level of complexity, I think this whole drive is a failure. It would definitely work, but the beauty of the system is how easily it is to engage.disengage and still ahve th bike feel like a normal bike. It only is worthwhile if it is simple and just works. Not if it turns into some complex system. Then you would just be better off going and buying a hub motor for your bike, and putting up with the weight and efficiency hit.

It will take a bit of time to get it working for low power, I just haven't got around to it yet. As I wanted to get the BrainBox hardware & first release of the software out for those interested in a higher power system.

- Adrian
 
Hi Adrian,

I look foward to the release of the commuter booster so I can ride the 30km round trip to work !

Love your work.
 
Update: 200-250w Limit performance

Good news. I just came back form a few test rides with the Commuter Booster on low power setting, and it all worked perfectly. :shock:

After posting my previous response above about how I wasn't happy with how the drive worked at low power settings, I realised I have change a lot since I did those tests. So I thought I should give it a go. Mainly I have tweaked the PID loops a lot. So it adaptively modifies the PID parameters to suit the power limit you set. This was initially done to give similar engagement for higher power settings, but also has improved things for low power setups too. :D I think last time I tested it I actually set 200w battery side, and had my PID control too slow to respond. With the new PID settings, and a more realistic battery side power limit set, it all seems good.

I set the lower power limit @ 300w. Remember this is the battery side power, not the output power.
The no load power for the motor depends on which motor you have. I was using the orange Turnigy 6374-200kv, which cold uses ~60w at full throttle, no load. Add another ~10w to keep the wheel spinning @ 50kph, then there are some additional losses when the drive is under load due to the rolling resistance of motor&tire contact, at low power levels this maybe around ~30w. (this really depends on a lot of things so can vary a lot)

Anyway @300w battery side, we should be seeing between ~250w on the road.

Now obviously this is not as exciting to ride compared to 500 or 1000w, but did give a gentle assist helping me maintain a good cruising speed, and make the hills feel a little flatter.

Frankly I was quite surprised. I am sure we test it more we will find some more quirks, that may require tweaking things a bit, but it looks quite promising. Thankfully.

- Adrian
 
That's awesome Adrian.

I've always wondered how manufacturers of ebike kits rate their kits eg is it power consumed by the battery or the power output of the motor after all losses are taken into account.
 
Okay, time to let others join the fun.

I have just posted For Sale threads for both the Commuter Booster and Brain Box.

So if you would like one or both, let me know.

Cheers, Adrian
 
Hey,

First of all I want to congratulate on the idea and turning it into an actual product :D

I am really looking forward to buying it but before that I want to dissolve some uncertainities:
1. Will I work properly with ZIPPY Flightmax 8000mAh 6S1P 30C ( http://www.hobbyking.com/hobbyking/store/__16228__ZIPPY_Flightmax_8000mAh_6S1P_30C_.html ) ? I want to keep the size to absolute minimum while still having capacity for week of short commutes with a little uphill boost
2. Does the BrainBox track motor temperature (I believe thats where the temp sensors goes) and prevent it from overheating?
3. What is the size (dimensions) of BrainBoxs 2nd part (the one without screen) ?
4. What motors are recommended for the smaller (50mm) swing arm version of CommuterBooster?
5. My greatest concern is overheating, so is it anyhow possible to attach a fan to the motor?

Happy New Year and Thank You :)
 
Hi,

Thanks for the kind words. It has been quite a journey.

Now for you questions.

1. Will I work properly with ZIPPY Flightmax 8000mAh 6S1P 30C
Yes. No problem.
2. Does the BrainBox track motor temperature (I believe thats where the temp sensors goes) and prevent it from overheating?
The brainbox currently has one temperature input (and expansion capabilities for more in the future).
It is up to the user to decide where they would like the temp sensor installed, but I only ever put it in the windings of the motor.
Current firmware only displays the temp, but it is possible to implement reducing the power based on the measured temp, just have not implemented it. If I was to implement it I would likely remove the datalogging feature, as I don't believe most people really need it, and it takes up half of the available programming memory.
3. What is the size (dimensions) of BrainBoxs 2nd part (the one without screen) ?
It uses the same size enclosure as the lcd/head unit (57x38x20mm).
4. What motors are recommended for the smaller (50mm) swing arm version of CommuterBooster?
I don't have a specific recommended 50mm motor, as all of the development effort has been on the 63mm motor.
But about 270kv is about right.
If you can find one with a skirt bearing it will suit high torque loads better.
Then I would just find one that weighs the most. This means it is likely to have the most copper, and surface area to handle the waste heat. As this is the biggest issue with the little motor. The little motors will be limited as to how much continuous torque they will be able to handle without over heating.

In fact that is likely the next feature I will implement in the firmware, a maximum torque limit. This has a couple of advantageous. It will allow me to limit the waste heat, without limiting the maximum power at higher speeds. It could also be used to reduce the loads on motor bearings, and tire wear at low speed, high power scenarios. Of course it can just be effectively disabled by letting it to a high enough number the limit doesn't get enforced, like the max speed at the moment.

5. My greatest concern is overheating, so is it anyhow possible to attach a fan to the motor?
Yes. Others have done this already, but I haven't bothered. I have been really happy with the performance of the 63mm motor with 500-1000w limits. Without any overheating issues. If you are worried about overheating, do not go for the smaller motor. You may save 300-400g but will have half the available power, and be much more likely to overheat.

Some of the motors are now coming with internal fans like the SK3's with skirt bearings. The external fans I have seen people mount are I think replacement fans from ducted fans. I think this is the link to one that has been used on a 63mm motor. http://www.hobbyking.com/hobbyking/store/uh_viewitem.asp?idproduct=4846
But this creates exposed blades spinning at very high rpm, so is not something I would recommend, but apparently it has worked at keeping temps in check.

I am currently taking a break and spending time with the family and should be making all the orders I have received next week.

Happy new year everyone ! ! !

Adrian
 
I had a email recently asking about ways to improve wet weather traction of the friction drive, suggesting using tire material on the motor, creating a tire/tire contact. I ended up writing a wordy respsonse that includes some theories on what the wet weather issues are, and potential solutions. I thought others may ahve some opinions so I will post it here:

This is probably a better conversation to have on a thread on ES, but here goes for the theory of what options we may have.

The issue with wet conditions is that as the tire rolls through the water, the water is pulled up off the road and remains in contact with the tire. By the time the tire has rotated around to where the friction roller comes in contact with the tire, the water has created a peak by the centrifugal forces. This water is then rolled over by the friction roller. We then expect the water to be squeezed out off this contact region. If enough water is squeezed out then there is enough contact area between motor and tire to sustain the required shear stress to transfer the drive torque.

With a smooth roller, and slick road tires the water ends up just forming a boundary layer and we lose traction very quickly. (In fact this is how bearings pull oil in to the contact region between ball/roller and the inner/outer races to provide lubrication and reduce wear.) With a rough roller, and slick road tire, the water has some valleys and cracks to hide in, while the peaks are able to break through the water to touch the tire and transfer the drive torque.

So option 1 would be to change the tire to something with some tread, to give valleys for the water. But if the roller is still smooth you end up relying on having a quite defined sharp edge to the grip tread. (Just ask the formula 1 guys how important a sharp edge on their tread is for wet weather grip). This sharp edge allows the water to be pinched out when the edge first comes in contact with the roller (or road), and can ensure you get contact direct from tire to roller/road. But during normal dry use this edge is quickly lost, and a friction drive is likely to wear it out too. But it would definitely be better than slicks.

Option 2 would be to use the rough roller. But this has the downside of having higher tire wear during normal operation. Lets explore why that is. Well it turns out that for the flexible tire to conform to the rigid roller, the tire does actually shear across the roller surface slightly, as the convex tire surface get pushed into concave, and the tire bulges sideways in the process. Now with a smooth roller the coefficient of friction between roller and tire is too low to exceed the shear strength of the tire rubber, so it just slides across the can. But with a rough roller the shear force can exceed the shear strength of the rubber, leading to wear. So what can we do to avoid this. (a) change tire material,
- perhaps a compound that can sustain greater shear before failing
(b) change tire profile geometry,
- by change to a tire with a flatter profile, the tire deforms less when conforming to the roller, thus reduce shear stresses, and wear
(c) change to a tire with tread that has tread blocks small enough to "sway" instead of locally shearing the rubber. This would also give space for water to escape. But small tread blocks will not be supported by the rest of the tire jacket like slick, so they will need to sustain more shear forces through the whole block.

Option 3 you suggested was a more compliant drive roller. This compliance could share some of the conformance, and shear loads. Therefore reducing the forces that can wear the tire. But for wet conditions we still need to stop a water boundary layer from forming. So we need to give the water somewhere to go, get rid of it before it reaches the drive, and have surfaces that come in contact that can help stop a boundary layer from forming, like sharp edges. The rubber on rubber contact may have a better coefficient of friction in dry conditions, but unless we stops the water separating the drive and driven surfaces, it won't work in the wet.

Personally I would put my research efforts towards a tire with tread first, and then second a rough roller of some sort that helps pinch through water to ensure contact. Pick some tire treads that give water somewhere to run, a flatter profile, perhaps small blocks not too high, and tightly spaced not an off road knobbly. Not to sure about the small blocks theory, as the blocks will tend to sway, leading to uneven wear...

The other thing we can do is reduce the drive torque when in the wet. Not ideal I know, as this me less assist. But I am in the process of adding a max torque limit to the software of the brain box which could easily do this.

Actually I might go do a bit of a search now and see what I can find.

Please note this is mostly theory at the moment, I have been considering this as a fair weather drive personally, and haven't done a lot of testing in the wet. As most of my electronics during development has not been water proof, so I have generally not taken the bike out in the rain.

Okay here are a few tires I might consider (based on a 10 minute browse of Chain Reaction Cycles)
Road Tires
http://www.chainreactioncycles.com/Models.aspx?ModelID=28140
http://www.chainreactioncycles.com/Models.aspx?ModelID=52622
http://www.chainreactioncycles.com/Models.aspx?ModelID=35763
MTB Tires
http://www.chainreactioncycles.com/Models.aspx?ModelID=28141
http://www.chainreactioncycles.com/Models.aspx?ModelID=8547
http://www.chainreactioncycles.com/Models.aspx?ModelID=53651
http://www.chainreactioncycles.com/Models.aspx?ModelID=24632
http://www.chainreactioncycles.com/Models.aspx?ModelID=3244
http://www.chainreactioncycles.com/Models.aspx?ModelID=51012
http://www.chainreactioncycles.com/Models.aspx?ModelID=53953
http://www.chainreactioncycles.com/Models.aspx?ModelID=11093

If/when I test this I will probably try a combinations of:
- few different tires,
- motor with and without grip tape,
- in the wet,
- possibly with different maximum torque setup, to ensure I have the same torque when I go through puddles independent of speed.

Then see what I learn.

A more novel approach would be to install an air blade (think dyson hand dryer) that blasts a thin high velocity jet of air at the tire jsut before the contact with the motor, to displace the water.

Well that is enough theory for now.

I might post this to my thread, as I may spark some other ideas.

Cheers,
Adrian
 
What a plausible explanation for tire slip during the wet, and an even better theoretical solution with blowing the of air across the tire before contact.

I'm amazed at how much thought you've put into this subject. Could brushes installed in a mud guard disperse water away from tire to the sides? Or a deflector before the water gets to the point of falling within the guard?

Limiting the torque of the motor in conjunction with water dispersion may just be the solution to wet weather commuter boosting - sorry, I couldn't help it :)
 
Chunkiam said:
Could brushes installed in a mud guard disperse water away from tire to the sides?

Nice idea. Even without mudguards you could mount something on the brake mount. Could probably make it something that just clips on for when you need it.
 
pedalix_motor.jpgpedalix RB-1.jpg

Has everyone seen this kit that won the eurobike gold award 2010 - kinda looks like the one you are working on.

http://www.pedalix.com
 
Quite different designs actually:
- motor in front of seat tube vs behind
- inrunner vs out runner
- belt reduction vs direct drive
- always engaged vs totally disengages
- low power vs high power
- simple pot throttle vs unique button throttle with multiple power limits and cruise control
 
I have an idea for a material that has not yet been tested for friction drive traction. It is a flat conveyor belt with a textile like surface and made of a material resistant to oil, wear etc. Since my power control for my friction drive is not finished yet I have only tried it through rubbing it against the tire but it seems as if µ is quite high. Could actually work great in wet weather also.

I found one on macmaster-carr that may be the same but now I can not find it. It is called flat conveyor belt and this particular one is used in the paper industry and built to minimize ESD. The one I got is 2,5" I believe.

 
Thanks for sharing.

Keep us updated on how it holds up once on the bike.
 
Sneak peak at the new controller under development for the commuter booster.

In keeping with the smaller, lighter is better principle. :D

P12238501.jpg

P12238300.jpg
 
Hi adrian,

I'm new to this forum and got in love with your friction drive. I own a road bike I'd like to boost but your template doesn't fit :/ :

commuterbooster.jpg


You confirm I have to change my bike or use a smaller rear wheel ?

Regards
 
Hi. Thanks for the kind words.

But unfortunately it won't fit that bike. :(

i really should get around to getting a model that fits behind the bottom bracket designed.
 
Yeah. Smaller wheels will give you more clearance to install the drive, but then (as kevo alluded to) rim brakes will now not match the rim size.
 
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