Belt slip stopper, idea.

[Barndom]

When the belt slips it have to lift out of the toothed pulley. If one can prevent this lift the belt can’t slip.

It can be done with a wheel on the outside of the belt, either active that are in contact with the belt or passive with it hoovering just a hair above the belt so it doesn’t create any extra drag under normal circumstances.

It may also be done with a passive guide the is just a hair outside the belt, but I think that when the belt lifts from the tooth it can be jammed between the pulley and the guide, even if a low friction material like nylon or teflon would be used.

It can also be arranged like an idle pulley that will prevent the belt from lifting from the tooth and also get extra wrap of belt around the motor pulley.

 

[torqueboards]

Why not keep the belt tighter that way the belt doesn't slip? If the belt is tight enough, you get better responsiveness and no slip.

 

[maxchilton]

already invented, it's called a belt tensioner.

 

[psychotiller]

Works great. Belt tensioners have been around for thousands of years :lol:

Here's one I made:
https://www.facebook.com/SiLo.socal.e.longboard.group/videos/vb.1431720757055488/1485489951678568/?type=2&theater

 

[pf26]

@Barndom: I've implemented you slip stopper idea on my Ebike with T5 belt. The motor pulley is small compared to the wheel pulley, which makes is more prone to slipage (pictures in the middle of the following llink, and the slip stopper was not installed at that time) http://velorizontal.bbfr.net/t19119p45-velo-couche-a-roue-avant-creuse-premier-proto
There is also a spring tensionning system, because the wheel pulley is not perfectly centered, but it would require too much force to prevent slippage in all occasion, and would create to much loss/wear.
The slip stopper improved the situation a lot, but it is quite difficult to make it "a hair above the belt" and strong enough to stay there. Also, I had issues of belt getting stuck between the pulley flange and slip stopper wheel. I noticed that lubricating the belt helps against this.
Anyway, I think this is a good idea. I prefer this slip stopper to belt tensionners as it does not require constant large pre tensionning forces, especially when you may have torque in both directions. But there is still some work required (at least in my case) to make it reliable.

 

[Barndom]

This is not a belt tensioner even if it can be placed to duoble act as one (or actually a pulley that wrap the belt to get more teeth in mesh, since the belt is supposed to be tight anyway). If one want to use a HTD-3 belt or a HTD-5 with few teeth en mesh to get higher gear reduction the belt can slip even if it is tight. This idea works in a different way and should en theory prevent slippage altogather (to the point the teeth really deforms, rips off or the belt breaks up) even if the belt is slack.

...
The slip stopper improved the situation a lot, but it is quite difficult to make it "a hair above the belt" and strong enough to stay there. Also, I had issues of belt getting stuck between the pulley flange and slip stopper wheel. I noticed that lubricating the belt helps against this.
Anyway, I think this is a good idea. I prefer this slip stopper to belt tensionners as it does not require constant large pre tensionning forces, especially when you may have torque in both directions. But there is still some work required (at least in my case) to make it reliable.

Nice to hear about it implemented I can imagine the forces being high and hard to adjust a 'hair above'. Maybe better to have it in full contact. Ofcourse new problems arise when going from theory to practice, but still sounds promissing. I like those wooden framed recumbents btw.

 

[pf26]

Just a pictures (taken using a mirror) to show my last implementation of the belt slip stopper, that now seems to work fine.

The roller (black) prevents the belt to slip
Surprisingly, it works both for traction and also regen (due to the position of the slip stopper, I though it would mostly work for traction only).
I wonder why I never saw any such implementation before, and nothing similar in timing belts engineering documents..

 

[Barndom]

Looks good

... . I wonder why I never saw any such implementation before, and nothing similar in timing belts engineering documents..

It surprise me also..

I was a bit worried that the motor axel and bracket could bend if the forces being big when the belt tries to lift, but see that you have an extra bearing on the outside of the motorpulley, which make it inherently stable.

Interesting to see a motor pulley mounted like a propellor, I’ve thought about that but never see it before. A lot of clever designs on that bike which may be usefull on skateboards too.

 

[spinningmagnets]

There is a factory electric bike that uses a pressure-roller to reduce belt-slip (ratcheting?), but I don't recall which one right now...I remember it was low-powered and expensive, and its rarity didn't have anything to do with the pressure-roller.

edit: I think it might have been this one (uses a poly-V belt instead of teeth)

https://www.electricbike.com/miele-evox-non-hub-electric-bike-from-procycle/

 

[pf26]

I think the belt slip stopper idea is more efficient when using timing belts, because you hardly need any pressure of the roller on the pulley. Pressure will build up when torque is applied and the belt teeth want to escape the pulley slots.
I use the slip stopper for 2kW motor with 1/17 gearing ratio. The motor pulley is very small and something is really needed to prevent slip.
The pulley mounted like a propellor + external bearing will limit the load on the SK6374 motor bearings (these little internal bearings I don't trust much).
It is quite easy to do since most parts are included in the motor delivery by HK.