RC motor on swingarm

Discussions related to motors other than hub motors.
This includes R/C motors, botttom bracket, roller and geared drives.
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LegendLength   100 W

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RC motor on swingarm

Post by LegendLength » Jul 17 2018 9:04am

I wonder if you would get much lever advantage by having the motor at the beginning of the swing arm, rather than a hub motor which is at the end of the lever?

For example dual friction drive which used 2 RC motors, and they drive the rim instead of the tyre:
pivot mount.png
pivot mount.png (191.13 KiB) Viewed 442 times
In that configuration I feel like you could use 2 kg motors and still the unsprung weight would feel a lot better than a 4 kg hub motor. But I'm not sure how to quantify it mathematically using forces and levers.

SlowCo   10 kW

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Re: RC motor on swingarm

Post by SlowCo » Jul 17 2018 10:54am

You're not the first to think about this:


velospeeder_velogical_sdc10357_v2_lr.jpg


Info:
http://www.velogical-engineering.com/ve ... rofittable

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LegendLength   100 W

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Re: RC motor on swingarm

Post by LegendLength » Jul 17 2018 11:02am

I have seen it but wonder about the idea of leverage and how much difference it makes to unsprung weight. Mainly so I can see how far you could push motor size in that configuration.

SlowCo   10 kW

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Re: RC motor on swingarm

Post by SlowCo » Jul 17 2018 11:36am

LegendLength wrote:
Jul 17 2018 11:02am
I have seen it but wonder about the idea of leverage and how much difference it makes to unsprung weight. Mainly so I can see how far you could push motor size in that configuration.
Basically if you go up in motor weight (x2) it will have a bigger effect on unsprung weight. And I wonder how much power such a friction system will be able to transfer to a rim. Especially when riding in sandy, dusty or wet conditions. I suspect a mid drive system through the chain will be a much better idea.

thepronghorn   100 W

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Re: RC motor on swingarm

Post by thepronghorn » Jul 18 2018 3:29pm

I = 0.5*M*R^2

Inertia is directly proportional to mass but proportional to the square of radius, so moving mass closer to the pivot point will decrease inertia a lot.

Your example of replacing a 4kg hub motor with 2kg of motor at let's say 1/2 the radius results in (1/2 the mass)*(1/2 the radius)^2 = (1/8 the inertia) that the motor adds to the swingarm.

ScooterMan101   1 MW

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Re: RC motor on swingarm

Post by ScooterMan101 » Jul 18 2018 4:02pm

+ 1 ( really + many people on this )

It is better to spend your design / mfg. time on a large RC Motor that sits on the swing arm right in front of the whee/tire .
A whole new swing arm will have to be made to accomplish this.

Do you have someone near you that can make a new swing arm ?
or
Can you do that yourself in your garage / shop ? ... if you have one.

I would like to find someone here in the South S.F. Bay area that can make a swing arm for me for a couple of reasons. one is to mount a RC motor in front of the wheel.

If you have access to a Machine shop, you do not have to do any welding, just make plugs , and or Lugs , and epoxy tubes into them. ( This is the way the first Tesla Roadster , and perhaps even all the newer Tesla Motor Cars are made. Look at the Chassis and you will not see welds on the chassis on the Roadster, it was over 90 % bonded together , mostly all Aluminum. )
So all you need to design and machine ( or Metal 3d print ) , is the plugs/lugs,
then
Get off the shelf tubing , carbon fiber tubing is available to buy .

There are two designs when doing a motor in front of the wheel.

Driving the cassette ( less power because bicycle chains can only handle so much power before they break )
and
Driving the left side of the bike, by using the 6 disc bolt holes to hold both a disc brake and a larger diameter sprocket. ( more power since you can now use stronger chains , but do not have the use of different ratio's )

Who here in the SF bay area can make swing arms ?

SlowCo wrote:
Jul 17 2018 11:36am
I suspect a mid drive system through the chain will be a much better idea.
My first conversion ...

https://endless-sphere.com/forums/viewt ... 1#p1077497

It's 2018 already, lets get some real , improved e-bike / e-velomobile / e-motorcycle designs .

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LegendLength   100 W

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Re: RC motor on swingarm

Post by LegendLength » Jul 19 2018 12:24am

thepronghorn wrote:
Jul 18 2018 3:29pm
I = 0.5*M*R^2

Inertia is directly proportional to mass but proportional to the square of radius
Awesome, i just assumed it was linear.

The main thing that attracts me about this setup is you automatically get 20:1 reduction with like a 30 mm diameter roller head. Normally you'd need a couple of mid drive stages to gear out a 100 kv motor.

My only real concern is how much power could be transmitted between a nylon roller and a wheel rim. I assume it would need a fair bit of clamping force to prevent slipping. If you sanded the rims and painted them with something a bit more grippy maybe it would allow 1 kw per motor without slipping.

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