Alternative Bike Friction Drive on Rim

[spinningmagnets]

but I still think it will suffer in the wet.

I was able to improve my friction drive step-by-step until I got up to about 1000W at 36V. On your system, the rim will be spinning at a high enough rate that most of the water will be flung off. I suspect that the fact you have two rollers grabbing the rim (in a pinching motion) will help with its traction. Perhaps even up to 1500W?

Even if the power that you use maxes out at 1000W before slippage becomes an issue, the question becomes....would you be happy with 1000W if it was very lightweight? If you are researching and making a prototype to see what customers would buy, I wish you luck.

The Yescom hubmotor is not light, but minus the battery/charger/and bike...They are only a hair over $200. I couldn't turn a profit using one motor. So...it will slip some in the wet...so what? I don't ride in the rain, and...if I am forced to go through a puddle, I may only have to pedal for a dozen yards or so and it's back to 1000W of motor driving me...

 

[Folken]

Here's a similar setup:
http://www.velogical-engineering.com/velogical-velospeeder.en.....

Fwiw, I test rode this at Aaron's Bicycle Repair in Seattle. Aaron had it mounted on a their spartan parts-bin shop bike. The unit's power was impressive for such small motors, in my opinion it pulled like a 250-watt geared hub. Motor whine was a bit louder than a geared hub. The package would be a nice boost on a lightweight roadie. Prior to the ride, I did some reading about it and assumed the motors flipped against the rim from torque like the designs from Adrian/Kepler/Hidden Power/Add-E, etc. The Velo does not work that way. Instead, it uses a handlebar lever and cable setup to pull the motors inward. That added complexity was disappointing [to me], but it was functional and the drive wheels didn't slip while climbing. IMO, this rim-drive idea gets more points than a tire drive.

Are you sure you tested Velogical setup? Nothing like you described is on their website.

 

[emco5]

....Are you sure you tested Velogical setup? Nothing like you described is on their website.

Positively the VeloSpeeder. It was back in July, and a product in need of refinement, so it would be a good bet that changes have been made.

 

[Folken]

Hmmm, I'm wondering what went wrong. I mean, they obviously didn't want the cable actuation, but there must have been a clear reason why they had to do it...

 

[cozy35]

Hmmm, I'm wondering what went wrong. I mean, they obviously didn't want the cable actuation, but there must have been a clear reason why they had to do it...

I wonder if this setup would conform to EU PAS laws? From what I gather is that PAS do not have a throttle and rely simply on minimum speed of 6 KM/h and cadence to activate. I may be wrong.

 

[emco5]

The challenge for Velo using cable, as I saw it, was the steep angle of the seatstays. Unlike Kepler/Adrian designs that allow the motor's weight to pull it away from the tire when the power is off, Velo needed to add springs at the hinges to keep their motors off the rims. That tension may have caused drive wheel slippage. If Velo mounted the system on the chainstays the springs wouldn't be necessary, but the problem with that could be road and chain debris.

The system was PAS with a crank sensor. It powered the motors even when pedaling backward which was amusing on hills.

 

[cozy35]

The challenge for Velo using cable, as I saw it, was the steep angle of the seatstays.....

My take is that because they are using a throttle setup the initial inertial motor swing was not sufficient to engage positively - hence they added the cable engage mechanism afterwards.

I think in a on/off push button system the inertial will be sufficient to overcome an adjustable spring tension for positive engagement.

 

[cozy35]

Update...

So, I made the VytaFlex mold casting the wheel out of SmoothCast Poly 300 and made the wheel as a one-part cast rubber/Poly wheel. It did not come out perfect and I suspect I would have to draw a vacuum on the mix before casting. The air in the mix caused a defect as can be seen in the picture as the stuff set hard. I am particularly worried about the bond between the rubber and the wheel. There is just not enough surface area and i am sure this bond will fail very quick when under load.

Looking back at what Spinningwheels said initially in this thread that he had a concern about the shaft failure and he recommends that the shaft be supported both sides of the drive wheel, it seems I will be back to the drawing board.

At this stage the project has it challenges but not impossible.

Here are some picutures...



Here the defects can be seen from the air in the two part mix before casting. I should have vacuumed the mix first.

 

[cozy35]

So now I have another basic idea.

Dual swing arms to support the shaft at both ends. The upper swing arm will hold a flange bearing.

This now means that I have to come up with a new pivot assembly with adjustable travel stops and an adjustable tension spring. I have a fair idea in my mind... now just to put it in 3D.

 

[Folken]

Still, I'm not convinced rim drive can provide a lot of power. Unless we are targeting the silly EU 250W restriction which is no fun.
My tyre driven friction drive holds 1kW no problem, but the contact patch is huge compared to the rim drive...

 

[cozy35]

Still, I'm not convinced rim drive can provide a lot of power. Unless we are targeting the silly EU 250W restriction which is no fun.
My tyre driven friction drive holds 1kW no problem, but the contact patch is huge compared to the rim drive...

I hear what you say. Tyre friction drives have been very successful and is the simplest form of bolt on power for bikes. Only one draw back - you are limited to just a few tyre treads and pressure surely will affect the efficiency quite allot. It will almost make off road riding possible.

Do you have your friction drive on the BB or the seat post tube?

 

[Folken]

Mine is seat post tube setup - inspired by CommuterBooster.

The efficiency... Let's say, when I force-hold the drive fully engaged, wheel spinning in the air at an equivalent of ~55-60kph, the draw is ~150W. The motor itself is 50W when the drive is disengaged. Surprisingly, some gear- or belt-driven systems show similar losses. I expect rim drive to be more efficient - unless it's slipping.

The tyre must be slick. Otherwise, the drive becomes very, very noisy. Even Schwalbe Big Apple is not "slicky" enough. Over time, my drive has "enhanced" its thread which made it really noisy. At least the efficiency stays the same regardless.

 

[emco5]

The challenge for Velo using cable, as I saw it, was the steep angle of the seatstays.....

My take is that because they are using a throttle setup...

There is no throttle, it's PAS.

 

[cozy35]

The challenge for Velo using cable, as I saw it, was the steep angle of the seatstays.....

My take is that because they are using a throttle setup...

There is no throttle, it's PAS.

But there is a lever for the cable engagement independent of the PAS?

 

[ozrider]

Hi cosy 35, Realy believe you're on the right track with this.Its been a year since your last posting about your rim drive build, what's the latest? If you're in production, I'm in the market for one.