Single stage RC left hand drive

[thepronghorn]

Inspired by FZBob's RC Mid Drive with Single Stage Reduction, I wanted a similar lightweight setup for the roads with a little more power. By running the chain all the way to the rear wheel, I can get similar motor torque and gearing to FZBob in his middle gears while still being able to pedal along in my highest gear.

6374 motor running through a #25 12:134 reduction to a custom sprocket adapter
Custom 3d printed compression 8S4P battery with Samsung 25R cells
Castle Creations HV80 controller
The system weighs about 2kg or 4.5lbs without the battery. The battery adds another 2kg.

 

[Grantmac]

Did you make the rear sprocket and mount?

 

[thepronghorn]

Did you make the rear sprocket and mount?

Yes it was all laser cut from 1/8" aluminum.

 

[Grantmac]

That looks much cleaner than I've previously seen laser cut, fantastic.

Did you have to machine down the hub at all?

 

[thepronghorn]

That looks much cleaner than I've previously seen laser cut, fantastic.

Did you have to machine down the hub at all?

I lightly deburred the backside of the parts since the laser does leave a bit of a burr on aluminum (steel cuts much cleaner). Otherwise I didn't do any machining. I was a bit worried about how I would keep everything concentric, but the 12 holes at each diameter sized for a "close fit" clearance hole make everything come together with very little play even before the nuts are tightened down.

 

[Grantmac]

So no extensive machining required? Did you offset the brake caliper?

 

[thepronghorn]

So no extensive machining required? Did you offset the brake caliper?

No I didn't do any machining. I just deburred the parts by hand with a deburring tool and a file.

The brake disc is offset by 1/4", so yes I had to offset the brake caliper. I also moved to a 200mm rotor for spoke clearance on the sprocket adapter, and my bike disc caliper mounts were conveniently 1/4" thick, so I was able to add the plate seen in the picture above to offset the caliper.

 

[crazy dreamer]

i like that a lot!

 

[Grantmac]

I wasn't aware that laser could do shapes so intricate and accurate. I thought you'd need to do extensive machining after.
What was the cost to get it done? Did you weigh it?

I almost think that stacked construction could be adapted to a belt setup running outside the caliper.

 

[thepronghorn]

I wasn't aware that laser could do shapes so intricate and accurate. I thought you'd need to do extensive machining after.
What was the cost to get it done? Did you weigh it?

I almost think that stacked construction could be adapted to a belt setup running outside the caliper.

Yep laser cutting works great! Low taper waterjet is better for thicker parts, but it's more expensive. I got the parts from sendcutsend.

All of the parts including motor mount, sprocket adapter, and disc caliper adapter cost ~$160.


CAD says the adapter weighs 500g without any of the hardware (24 8-32 stainless bolts and nylock nuts are ~100g more). I think it's pretty well optimized (price/weight) for laser cutting.

There is room for a belt pulley in place of the sprocket since it completely clears the outside of the brake caliper. The main difficulty with belt drive is getting the belt through the rear triangle. You have to cut the frame or do some fancy belt pathing with idler pulleys. I have thought about cutting the seatstay and reinforcing it with a "splint" to get the belt in, but I am apprehensive about cutting my frame. The chain noise is not that bad. The chain is only running about twice as fast as the pedal chain. The motor makes much more noise right now which could be improved with a sinewave controller.

 

[district9prawn]

Nice parts, I really like the brake/sprocket adapter.

Is regen or braking possible on the castle controller?

 

[thepronghorn]

Nice parts, I really like the brake/sprocket adapter.

Is regen or braking possible on the castle controller?

Thanks! Your bike was another inspiration for this project. Unfortunately the castle controller does not have regen. I'm thinking of getting a VESC for the torque throttle and regen capabilities. The castle controller also faults from overcurrent if I give it too much throttle from a start, probably because I have the motor geared so high, so that's annoying as well.

 

[BalorNG]

Hey, that's really cool! But frankly a ton of work that could be easily accounted by regen braking with a vesc - you already have a front brake as backup (though with a small battery you cannot have too much regen current before it starts killing your battery).
Still, this method of laser cut '3d printing' of sorts is cool. Gotta have it in mind.

 

[neptronix]

I love how simple and lightweight this is. You should literally sell it as a kit. It would work on so many bikes. Certainly superior to a hub motor.

 

[SlowCo]

Great build Pronghorn! Very sleek and elegant :thumb:

There is room for a belt pulley in place of the sprocket since it completely clears the outside of the brake caliper. The main difficulty with belt drive is getting the belt through the rear triangle. You have to cut the frame or do some fancy belt pathing with idler pulleys. I have thought about cutting the seatstay and reinforcing it with a "splint" to get the belt in, but I am apprehensive about cutting my frame. The chain noise is not that bad. The chain is only running about twice as fast as the pedal chain. The motor makes much more noise right now which could be improved with a sinewave controller.

Belt drive can be done like the LMX Bikes have:

 

[thepronghorn]

Thanks neptronix and SlowCo.

I have seen the LMX belt style - its main shortcoming is that it doesn't look like it would regen well. The LMX bikes have freewheels, so it doesn't matter for them, but I would like my bike to have regen. I purchased a cheap FOCer from helno that I still need to install on the bike. This should give me regen capability and get rid of the overcurrent faults I was getting on the CC esc.

 

[Grantmac]

On a hard tail you can run a fixed belt tensioner which would be fine with regen.

I think the inefficiency and inability to run a really small pinion would be the biggest issue with going belt for your bike.

 

[Grantmac]

I had forgot to ask, what speed does it provide assist up to? Have you considered going multi-stage to reduce rear sprocket size?

 

[thepronghorn]

Right now it's geared for 160Kv*29.6V*(12/134 gearing)*(29*pi wheel OD)/12/5280*60=36mph. At full charge, it goes about 32mph which drops to about 27mph by the end.

 

[Grantmac]

Pushing the full 80 phase amps? How many battery amps?

 

[thepronghorn]

Pushing the full 80 phase amps? How many battery amps?

30mph takes the standard 1000W or so. I usually put about 100W in myself, so 30A battery cruising is pretty normal. The motor is dissipating about 100W at this speed and current, so it gets pretty toasty. I'm not sure how long it could actually sustain this power - the longest I've ever gone straight is about 8 minutes/4 miles since my battery is quite small.

.... Have you considered going multi-stage to reduce rear sprocket size?

I really don't want to add a second stage of gearing for efficiency/weight reasons. I'm not sure why I would want a smaller rear sprocket? As it is, the rear sprocket can't be much smaller since it has to fit outside the disc caliper which has to fit around the 200mm disc rotor which has to be that big to give clearance between the spokes and caliper for the sprocket adapter.

I have considered going with a larger rear sprocket for lower gearing combined with higher battery voltage for more power. Since the sprocket is laser cut, it's pretty easy to get different ones made.

 

[Grantmac]

I was thinking more about a larger front sprocket to reduce noise and wear. Possibly doing the first stage in belt to reduce noise.

Also my application is a bit different in that I want no faster than 20mph and less is fine, but maximum climbing capability. Possible with a 12s to keep current down.

 

[thepronghorn]

I was thinking more about a larger front sprocket to reduce noise and wear. Possibly doing the first stage in belt to reduce noise.

Also my application is a bit different in that I want no faster than 20mph and less is fine, but maximum climbing capability. Possible with a 12s to keep current down.

If you need more climbing ability and you're concerned with noise, you probably just need a bigger motor than I'm using. Perhaps an 8080 or 80100 or even a 12070. Two stages works too, but one stage is nice and simple.

 

[Grantmac]

There is definitely a sweet spot between putting the weight into the motor vs adding extra reduction. Generally going bigger on the motor also requires bigger batteries where adding reduction does not so long as you have a modest expectation for max speed.

1500w should be plenty for what I'm after so long as it can be reduced to a reasonable RPM without making a bulky or heavy drive system.

 

[alpaca123]

I had a question for thepronghorn which was answered along with the advice to post it up here so please see below:

Howdy thepronghorn,

I was wondering what grade of aluminum you used for your left hand drive sprocket components (5052, 6061?)? Did 1/8'' material work well for a sprocket with a #25 chain? Did you upgrade your controller to get regen and if so how does it feel?

I am planning a similar left hand drive set-up, and I am almost ready to get some metal cut once I get everything sized right to my frame (3d printing soft prototypes).

Thanks,

Alpaca

Hello! I used 6061 aluminum. 1/8" material is working fine. It's a pretty close fit, but I filed the teeth to get a little narrower at the tips and haven't had any issues.

I am now running a cheap focer 2 VESC which is capable of regen, but I have not implemented it yet. I just bought an erider T17 BB from ebikes.ca, so I am looking forward to ditching the throttle and getting a more intuitive "pedal assist" feel when it arrives.

I will caution you that the long chain annoys me a bit, so long term I am hoping to test out a configuration like mxlemming uses with the motor mounted off the disc brake mount.

In general, this type of conversation is best aired out in the main forum in case other people have similar questions, so feel free to ask questions there if you're comfortable.