FS: Commuter Booster Friction Drive Beta Units

[cwah]

Hello,

I'm thinking of buying a new Dahon Uno and add the commuter booster to it:


Seat tube size is 34 x 580 mm (forged aluminium clamp). full specs here: http://www.evanscycles.com/products/dah ... 9#features

Do you think it could work?

[adrian_sm]

Do you think it could work?

Yes. But..

Check out this thread. viewtopic.php?f=28&t=31457&hilit=folding

It is definitely possible, but you are very limited in the where you can place the drive on the seat tube. This limits the adjustments you can make. Normally you adjust the angle at which the motor contacts the tire by sliding the drive unit and down the seat tube. But you can't really do this with the Dahon. So I think ferias77 adjusted the length of the swing arm instead. Essentially changing the distance between the swing arm pivot point and the motor mount. If ferias77 could confirm the geometry I may be able to modify a Commuter Booster to the same specs. The important things are:
- seat tube diameter
- distance between pivot axle and seat tube
- distance between centre of pivot axle and centre of motor axle
- motor diameter
- angle between main pivot/clamp block and swing arm at initial motor contact with the tire

If you are lucky the geometry will be the same as the Commuter Booster, but I can't be sure unless we check. Sorry for the extra effort required but the drive unit is not really designed for this type of bike at the moment. You may be better off going for one of Keplers eBoost units if mine can't be adapted.

- Adrian

[cwah]

Ok thanks Adrian.

I'm not a very technical guy, I'm going to ask Kepler.

But I'm not sure if it's working either (and it seems to be out of stock).


By the way, I'm just looking for a folding bike I can carry on the public transport (bus and tube). So if you have anything working in mind I would be interested.

ps: I'm still wondering if I should buy this bike. If I buy this dahon uno and I get a ruler. I should be able to measure the distance and angles. Would that be enough for you?

[adrian_sm]

From a number of emails I have received.

How can I use a normal twist/thumb/analog throttle with the commuter booster?

The brain box is currently optimised for use with the digital button throttle. In the future I will be modifying it for use with analog throttles, but not yet. Sorry.

If you are keen on a twist throttle the options instead of the Brain Box are:
(1) Buy a RC Cycle Analyst from ebikes.ca
- here is the ES thread
- here is where to buy them from

(2) Roll your own
- modify a servo tester to accept a hall throttle, and output the correct signal for the ESC. Here are the instructions
- I would also recommend using a one of these to adjust the ramp up rate. This helps smooth drive engagement/disengagement.
- this is a very basic and cheap setup, so it will not enforce any minimum speeds, or limit maximum power. So beware!

Cheers,
Adrian

[crusoe]

Do you have any videos with you actually riding with the booster?

[adrian_sm]

Hey,

I really need to spend some time and get some better videos, but here is one from on-board during a recent group ride. It gives you an idea of the sort of speed and sound to expect when I do accelerate off. This was with the drive restricted to ~700w.



And here is an older one, with the drive on a mountain bike. The camera setup was very average so it is pretty shaky, and all the drive noises are amplified, but at least it shows you how the drive engages.

[adrian_sm]

Update:

Hi everyone. The holiday season is over for me and my suppliers now, so I'll be finishing of the drive units soon and contacting everyone to confirm the order, arrange payment, and ship things out.

Thanks for your support and patience.

Regards,
Adrian

[adrian_sm]

Update:

Thanks for everyone's patience. The holidays didn't leave any much time to make kits, and I have had to convert my garage into an office workshop to give me the space this little project needs. Unfortunately this means I won't have the workshop functional for a few more days yet. The good news is that I have the CBs 90% made, enough parts for the Brain Box's, and my family is interstate for a week more so no distractions.

Again sorry for the delay, but I really need to make a dedicated space to work on the Commuter Booster to make production more efficient. I hope you all understand.

Regards,
Adrian

[adrian_sm]

System Design:

I have had a few people asking component select questions, so thought I would post the basics here.

Volts & KV, and assist speeds
You need to select a battery voltage, motor diameter & motor KV to give you no load speed slightly in excess of you required maximum assist speed.
For example I recommend a 5-6s Lipo (20-24v) 63mm motor with 200kv. This gives a no load speed on 20v of 47.5kph, and 57kph on 24v. This means I still have a level of assist up to these speeds, and keeps the motor and ESC happy. Running at a higher voltage would require more expensive ESCs, that would just end up having to PWM the phase current more to keep power levels down at the same level, putting the ESC under more stress. Picking a motor with a higher KV will give less torque, and have the motor running at lower efficiency for the normal operating speeds, resulting in more waste heat and lower sustainable power levels.

A quick equation for the no load speed is:
kph = battery volts * motor diam in mm * motor KV / 5305
mph = battery volts * motor diam in mm * motor KV / 8538 [Edit: corrected]

Note: The no load speed is where the motor provides no work, so for the real assist speed drop this number down a bit, and calculate it at the depleted battery voltage.

Battery Selection
I recommend 5s or 6s LiPo batteries. These are cheap, energy dense, easy to parallel up, easy to balance with an RC charger, and don't require the high voltage RC ESCs. You could also pick 4s, but these will require high KV motor to compensate, and require high battery currents for the same power.

Motor Selection
Apart from picking the right diameter and KV as mentioned above, getting the heaviest motor will allow it to handle more power. As it has physically more mass to absorb the heat and larger surface area to dissipate it to the air.
A motor with a skirt bearing will resolve the tire contact forces better, and give longer life.
A small diameter motor (ie. 50mm) will fit smaller frames, but will not be able to deliver as much power.

If you are happy with ~500w power levels you could probably get away with a 50mm diameter motor. But I will usually recommend the 63mm motors

Power Limiting
A normal RC ESC and motor combination does nothing to limit power levels. This results in lots of power but is also likely to overheat, loss sync, wear tires due to higher forces. That is why I recommend either using my Brain Box, or the Cycle Analyst -LRC. These have closed loop controller of power/current and enforce a minimum speed to maintain the health of the system, amongst other advanced features. Some people (most notably Lyen) have been experimenting with the sensorless ebike controllers so these may also be an option soon.


So please feel free to roll you own system design and electronics, but also be aware of the limitations of friction drives, RC motors and ESCs when doing so.

- Adrian

[adrian_sm]

Oh and here is a picture of a bike I pulled off a rubbish pile and turned into a single speed test mule. Just cost me $120 for new wheels, tires and chain. Plus a spare saddle I had. The ride is a bit harsh compared to a modern road bike, but I still like it. As pictured it weighs about 15kg, does 50kph.

[full-throttle]

bullhorns - check
coloured tyres - check
coloured chain - check

all you missing is a card in the spokes, a Knog Frog flasher and some skinny jeans

[adrian_sm]

I'll pick them up next time I am in Fitzroy.

I rode this bike in to the Sustainability thing on at Birrarungma the other day. Single speed and electric assist was a nice combo. But I had it on 6s, and I can't keep the cadence up at 50kph. What gearing do you run on the BPM hardtail?

[full-throttle]

I rode this bike in to the Sustainability thing on at Birrarungma the other day.

Hence the green combo

When I was using BPM code-9 (55kph top speed) the ratio was 52/16 and I was still topping out.

With code-12 (40kph) and 48/16 it's just right.

My singlespeed roadbike is 44/15 - comfy at 25-35kph, top out at around 48kph.

[adrian_sm]

Mine is 52/16. Maybe this will teach me to spin.
But I think I will run it on 5s in the future.

[cwah]

Hello Adrian,

Got another bike (Pacific If Reach) I was wondering if it may fit:


Asked Kepler but his config wouldn't work directly. Any chance it may work with your friction drive?

[adrian_sm]

That would be a custom design which I unfortunately don't have time for.

Sorry.

- Adrian

[cwah]

Ok thanks Adrian

[deepfraught]

Great video of the Melbourne e-bikes ride.
Looking forward to the new units, I think I'm believing the 40kph top speed is the sweet spot.
The 2nd speed option to get "Give it all you've got Scotty" power sounds nice for those power hungry speed times.
I did a battery range test on hub motor at full steam and found 50kph+ blustery wind in ears, tiring noise and concentration for shared path traffic/obstacles.

[adrian_sm]

Quick pic of the next batch of CB's ready to ship.

fr_965_size640.jpg (159.12 KiB) Viewed 1017 times

[adrian_sm]

New manuals are currently being uploaded to the website. Sorry about the huge file sizes, I couldn't be bothered working out how to compress them. The manuals are still not perfect, but should be good enough for most of you.

- Adrian

[deepfraught]

Received beta unit and Brain Box today, thanks Adrian
Adding feedback to your development thread.

[adrian_sm]

Glad to hear it arrived safely. Looking forward to hearing your impressions.

- Adrian

P.S. I hope I sent you the correct size, unlike one unit I had to resend to Singapore.

[adrian_sm]

Oh, and for all the beta testers. I erred on the conservative side for the dead stop controlling how much the motor can swing towards the seat tube. If this is restricting your installation it can be modified.

Cheers, Adrian

[adrian_sm]

Cheap Motor

Leader Hobby have the 6364-230kv motor for cheap at the moment. I haven't tried this motor specifically, but have been very happy with the 6374-200kv bigger brother.

Anyway US$33 is a pretty darn good price. I just bought five to build up some demo units. So if you have bought a kit recently and have yet to get a motor, this could be a good choice.
http://www.leaderhobby.com/product.asp?ID=9394001224158

[kevo]

Adrian,
Any idea why they are offered so cheap? What does the Turnigy SK3 have that these don't.
Less than half the price is significant, thanks for pointing out this source.