DIY crank drive ideas please

[andyh2]

Inspired by this set up for a yuba cargo bike;
Urban Commuter Store

I'm considering seeing if I can get the kit supplied without the motor and electrics so I can source them in the UK. And I'd like to tap into the experience here...

This set up is designed to take a rear 135mm drop out motor which can run a disc. I assume a front 100mm drop out motor, that can take a disc, could be made to work, but would require some adaptation.

My first inclination would be to go for a Bafang 36v 250W rear motor as it would be legal (provided gearing adjusted accordingly) and easily available here.
Are there any alternatives I should consider?

I could use a direct drive motor, which I understand would be bigger, heavier, but also quieter. Would it be any more or less reliable? Any recommendations for legal DD motors?

Given that the gearing could be adjusted to suit motor speed is there any advantage or disadvantage in choosing a higher (eg designed for 20" wheel) or lower (eg for 26" wheel) speed motor?

Thanks

 

[eddieo]

As cargo bikes go not bad looking...But do you really need this for everyday use? a normal e bike with trailer makes more sense, unless for say a daily delivery service or business.....The powerful Ezee kits with large battery looks just about right for this bike IMO

 

[Scottyf]

You would be better off suited to a geared motor as you've described.
The problem with a direct drive at legal power speeds or ratings is that it won't have the effciency or lower torque you require. It would take more amp's to effectivly pull the bike around at the same speed as the geared.

However from what I read the direct drive once up to the speed uses a lower amount of watts to keep it there. They are generally more reliable and have less moving parts than there geared buddies too.

If I was designing that I'd pick a motor with the least Rpm. As your driving through the gears the motor will spin less Ie 190rpm max to get the speed required. It also gives greater flexibility to stay in the sweet spot for effciency. Also means you can match the gearing a bit easier.

Technically speaking though on the above it doesn't matter what Wind you go for you can just match it with the right volt and amps and the limits are the size of stator and copper fill of every motor.

However in practice it will be better going for a lower rpm one and then using 36v battery. It would give the composite gears and easier time than trying to spin at 250rpm instead of 190rpm.

Good luck with the build and let us know how you get on.

 

[flecc]

Frank's post on this link mentions an SB motor already adapted for this sort of application.

 

[andyh2]

Flecc - Frank's set up looks good, I think I'd prefer something that had readily available spares though, rather than one off parts.

Eddio -I've got a pro-connect, which is great, but I have to think about replacing the battery as I'm down to 60% capacity. The Yuba would be more versatile eg 2 kids (7,8) to the park and pick up the shopping on the way home. I do need to get a test ride on the current version to check how the ride compares to the PC.

Scotty -thanks sounds like lower speed Bafang would be the way to go.

 

[Deleted member 4366]

The gearing on the Bafang is perfect. If you look back through my posts for Bafang crank drive, there's details of sprocket sizes, but basically I used a rear motor with a single rear free-wheel sprocket to a standard size chainwheel and the gearing was perfect to give full power at a bit more than my natural cadence of about 70. The main thing I learnt from the project is that the motor needs to be mounted very rigidly otherwise the chain jumps. There's loads of fotos in my photobucket folder that might give you some ideas.
Bafang Crank drive pictures by d8veh - Photobucket
Another suitable motor would be the Cute, which is similar to a Tongxin and should work well as a crank motor.

 

[andyh2]

I'd forgotten that nice conversion from a couple of months ago. What speed motor is that you're using?

Am I right in thinking you could have simplified the installation by using a bolt on disc cog, but would then have lost the freewheel on the motor ie you'd have the same level of drag when pedalling without motor as you would when using motor in normal hub configuration?

 

[Deleted member 4366]

I had to used a freewheel to make sure that I didn't get any drag from the motor and also because I had the bits lying around. Yje notor has a freewheel as well, but I would've been spinning it quite fast all the time, which I wasn't sure about. I'm going to have another go at this soon. I've alreeady bought a Cute rear motor, which will be adapted slightly to make it smaller, and I bought a special free-wheeling chain set so that I can drive on the right side. It was about £75 from Cyclone. It's a bit on the heavy side though.

 

[andyh2]

That looks neat. I guess you loose a chainring so don't get full gear range, probably still plenty wide enough though.

Would that mean you'll have to machine a front hub to accept a sprocket on the RH side?

I know there are freewheel BB / cranks available for trials bikes. I wonder if one could fit on LH side, then a standard front hub, with rotor mount bolt on sprocket, could work and not have to drive the motor, or use motor and not have to pedal.

 

[kitchenman]

I know there are freewheel BB / cranks available for trials bikes. I wonder if one could fit on LH side .

Thats what I need on my stokemonkey. Do you have any links?

 

[Scottyf]

I love the idea of a hub driving through gears.
As hubs are generally very quiet. Unlike friction drives or Rc motors with super high rpm's.

However I don't think they really look that stealthy and there never really appears to fit in with the look of a bike. However you would get the best of both worlds with high torque and high speed should you need it. (Even though not legal).

Also another good thing is you could chose how effcient the motor could be. Ie just let the rpm on the motor be its max to get the best effcieny. Instead of the hub being stuck in one gear.


My amp useage goes through the roof when It has to climb or if there's strong winds. If I was able to down change I could get the motor to use less energy.

 

[Miles]

Thats what I need on my stokemonkey. Do you have any links?

Cranks (Pair)

Of course, you won't be able to isolate the cranks from the motor on a LH side drive.

 

[Miles]

or use motor and not have to pedal.

This bit wouldn't be possible, I'm afraid.

 

[flecc]

This bit wouldn't be possible, I'm afraid.

Unless a freewheeling chainwheel like this one from cyclone-tw is used:

 

[Miles]

I know there are freewheel BB / cranks available for trials bikes. I wonder if one could fit on LH side, then a standard front hub, with rotor mount bolt on sprocket, could work and not have to drive the motor, or use motor and not have to pedal.

This was the context, flecc. A hub motor driving the LH side of the BB. At least, that's what I assumed.

 

[flecc]

I agree Miles, my post was just a suggestion to reverse that arrangement, not a disagreement with what you correctly posted.

 

[Miles]

Sorry I misunderstood! I should have known better

 

[flecc]

The apology should be mine Miles, I probably shouldn't have quoted you in that other context response.

 

[Miles]

No problemo

Here's a thread that we had on Endless Sphere, highlighting an issue re. the suitability of various freewheels for use on freewheeling cranks:
Endless-sphere.com • View topic - Destroyed! A warning to those using freewheel cranks....

 

[andyh2]

Another crank link;
Cranks - Rock `n` Roll Bikes

and an endless sphere discussion here;

Endless-sphere.com • View topic - Freewheel crank resources