Bob's very simple <1kW friction drive

krik said:
Hello folks,
there is mention of speeds of 15 & 20mph for this kind of drive - what happens when you are going down hill 30+mph and the drive is still engaged?
Does something get fried or it just not pull any amps?!
Click to expand...

My friction drive tops out at around 28-30 mph so I've had to think about that exact issue.

Most people using friction drive on here are using some kind of arm or sliding mechanism so when the throttle is off the roller (or motor in some cases) is off of the tire or almost off the tire.

My sliding setup is always a bit engaged so I use a roller that has a one way bearing inside so it freewheels when not being used.

All that being said, I have my roller a little too far back on my bike so I sometimes spin the motor when I don't want to. I use a Castle Creation hv85 and I haven't had any issues with that. I have heard that the newer Castle esc's don't like it as much and will pop. So it seems it just depends on the controller.

I assume it wouldn't be a big problem if you used a ebike controller. Most of us are using an RC esc with our setups.
 
krik said:
Hello folks,
there is mention of speeds of 15 & 20mph for this kind of drive - what happens when you are going down hill 30+mph and the drive is still engaged?
Click to expand...
Not an issue !
As EVTodd said, it simply will not be engaged if it is designed correctly with either a "swing" or "slide" engagement mechanism, or a roller clutch bearing in the drive roller.
With either of these systems, any "overspeed" ( even when you cut the throttle at low speed) will immediately disengage the drive.
 
Bob,
on your setup it looks like the two arms pivot just behind the seat post and you can set the movement distance using those screws. Does anything pull it into contact or just the action of turning the motor on? (also looks like you need a couple more folds!)


Thanks EVTodd & Hillhater; was considering a basic test using a fixed outrunner in contact all the time.
Is it the 'overspeed' that damages the controller or just spinning the motor with controller/power off?
i.e. could i still fix motor and just not go over the max rpm of the motor/esc?
 
Hi Krik
I was going to experiment with a light spring on the other side to the limit stops. It swings on bearings so should move pretty freely.

In constant contact I doubt a human would have the legs to overspeed such a setup. But a goodly downhill could do it...
Overspeed onto a BLDC motor will eventually overvolt the controller via the inverter diodes in the ESC (& the motor's kV).
It is possible to control into overspeed by "field weakening" but it's a difficult undertaking & cheap ESC's aren't designed for it.

I should be able to get back onto this fairly soon - my workshop extension is nearly done....
 
back on with this, I made the steel roller, clamp plate & tapered olive on sunday, I'll try to get it together tonight & take the odd picture :D
 
bobc said:
back on with this, I made the steel roller, clamp plate & tapered olive on sunday, I'll try to get it together tonight & take the odd picture :D
Click to expand...

Looking forward to it! There hasn't been much friction drive goodness on the forum for a while. :D
 
here we go
frdrive_zps7c11dbca.jpg

I turned the shaft round in the motor so that the circlip groove wasn't the ultimate stress raiser in the wrong place, the roller is held in place by a taper lock: the seatpost clamp is not on in the photo but I'll take a snap of it on-bicycle in a day or two. It feels really solid, looking forward to seeing if it holds together (or SM's dire predictions come true.....)
TTFN
 
So - burning question - will my heel strike that sticky - out motor?
I guess not!
heelmotor_zps3d20d14e.jpg

The seatstay clamp bracket will have to be remade however to move the whole arrangement to the right place on that bike.
I'm on it.....
 
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