Belt drive Sprockets on the Cheap!

[katou]

This thread is so I'm not tempted to clutter up Recumpence's thread about his awesome new belt drive for the KMX trike.

Here's my background: I made a series of small 3" dia epoxy pulleys to use a timing belt I got from a surplus store. The teeth stripped off. I believe that this was due to too much stress per tooth. I should have made the pulley much, much larger. The molding went well, with very little mess providing that I bulked up the epoxy with some filler (colloidal silica from West System).

Another member, E-Racer, has had better luck, ie, no teeth stripping provided the pulleys/cogs were 6" diameter or larger.

It appears from AussieJester's build log for his HXT chopper: http://endless-sphere.com/forums/viewtopic.php?f=28&t=12810&start=300

That he also tried it out. I didn't follow the thread long enough (104 pages) to figure out what happened with that effort.

Did he end up using them? If not, why?

I'm keen to figure some of this stuff out. Anybody want to show me how to calculate loading per tooth?

This method seems like it would work, and be fairly easy to try out.

Other options, castable urethane comes to mind.

Katou

 

[spinningmagnets]

I think this has potential. Having a large enough diameter pulley might mean the chain end of a drive can have a more reasonable range of acceptable sizes. It might also mean that a builder could to achieve his goals with a single reduction instead of needing a 2-stage.

Spoked V-belt pulleys can be found very easy in many diameters, and its a cheap experiment. Perhaps the teeth that came off would have held if the epoxy was thicker? or even maybe if the metal under the teeth was scored with grooves by a dremel to give the epoxy more "bite"?

 

[AussieJester]

It appears from AussieJester's build log for his HXT chopper: http://endless-sphere.com/forums/viewtopic.php?f=28&t=12810&start=300

That he also tried it out. I didn't follow the thread long enough (104 pages) to figure out what happened with that effort.

Did he end up using them? If not, why?

Yes he did use them and yes it worked brilliantly while in use, no lost teeth etc. If i had bought a slightly smaller pulley orginally, it would still be in use today however the gearing was a lil low so sprocket and chain was installed to change gearing. I did have belt slip issues around this time it was eventually traced to the first stage reduction belt slipping this was also changed to chain.

KiM

 

[E-racer]

I'm going to go ahead and bring this method over from recumpence thread as well. I think this is the way I would do it now over the epoxy method.
Stacked 1/8 plate water jetted, and glued or welded together. You could use aluminum for the Master "hub" plate and plastic or aluminum for the rest. This method allows you to configure different offsets or belt widths. Making one of these would be a breeze if you have access to a water jet or laser. I may even give it a shot with the cnc plasma I have access to (surface finsh wont be as ideal as water or laser).

 

[E-racer]

Also for anyone designing belt drives; I've done a bunch of these for robots and small vehicles. Belt wrap on the small pulley is VITAL! Most belt drive systems that don't work have on fatal flaw which is a 2 pulley setup. With one tiny pulley and one large you are very limited in the amount of wrap you can get on the small pulley. Idlers in belt drives are a necessity if you don't want to run a wide belt for no reason. There is a reason OEM's use so many idlers in their timing belt drives. If your belt drive is stripping teeth off the belt add an idler!

It's pretty easy to guess which one of these will work better.

 

[1000w]

This setup of mine has been faultless for about 2500km and the teeth show basically no wear at all. The load is shared by many teeth all the time.
http://www.endless-sphere.com/forums/viewtopic.php?f=6&t=10337&start=15
Cheers,
Matt.P.

 

[E-racer]

This setup of mine has been faultless for about 2500km and the teeth show basically no wear at all. The load is shared by many teeth all the time.
http://www.endless-sphere.com/forums/viewtopic.php?f=6&t=10337&start=15
Cheers,
Matt.P.

WOW nicely done man! I've made a couple pulleys just like that, yours came out great! I don't know how I've never seen your build before beautiful bike!

 

[Miles]

I've always been meaning to experiment with a lantern gear type construction

Might get away with a skip-tooth pattern....

 

[E-racer]

That would look so cool on a bike! That's a helluva Lotta holes to drill and pins to put in :-D I think you could get away with a skip tooth as well. I love that ppl are posting more cad pics lately makes these threads look good.

 

[bobc]

OK here's a nice render of my original water jet cutting suggestion.
top picture is the blank you'd get water jet cut in 25mm ally
2nd picture is after generation of a large pile of swarf ;^)

 

[Miles]

top picture is the blank you'd get water jet cut in 25mm ally

I've no experience of water jet cutting. How feasible is it to get something like this cut with kerf-taper compensation?

 

[adrian_sm]

I would be concerned about the quality of the surface finish you get from waterjet cutting, especially for thicker stock.

Here is an example of a medium quality finish that I got for some parts I recently got cut for me. You can get better finishes if you have slower feedrates, but there is no way I would use the finish I got to run a belt on.

 

[E-racer]

I think the kerf angle would be severe enough to make a belt not track properly in 1 inch plate. That's why I proposed the multi plate design. I water jetted a 1.25" oil pan spacer thing for a GSX600 motor in a FSAE car, didn't even end up using it the kerf was so bad on one side :-/ Laser might be a little better. For a timing belt to track straight the teeth are going to need to be really true.

As for the surface finish. Ive seen very good surface finish on thin stuff (even at high feeds). The deeper the cut gets (thicker material) the rougher the cut is. 1/8 plate and hit the teeth with a quick 200ish grit sand paper you are good to go. A laser really would be the way to go. I cut a brake rotor with one and the surface is literally perfect, it loos die cut.

BTW, I hate all of you guys... Ya'll are making me want to go to a belt drive on my E-bike. Not only will this be more unreliable than chain, its nearly impossible to package the way I want. Its just so smooth and quiet.... AHHHHHH!

 

[John in CR]

Do the large diameter pulleys really need teeth?

Miles, I like the lantern gear rig, though I think I'd go double sided with the disk for almost no extra work. If the epoxy route didn't seem so easy, I'd give that a go.

 

[recumpence]

Do the large diameter pulleys really need teeth?

Miles, I like the lantern gear rig, though I think I'd go double sided with the disk for almost no extra work. If the epoxy route didn't seem so easy, I'd give that a go.

That depends on the belt tension, pulley diameter, belt wrap, belt and pulley material, and torque applied. Most clothes dryers use a stupidly thin (maybe 8mm or so) ribbed belt wrapped directly around the smooth drum. They hold fine with proper belt tension.

Matt

 

[John in CR]

Do the large diameter pulleys really need teeth?

Miles, I like the lantern gear rig, though I think I'd go double sided with the disk for almost no extra work. If the epoxy route didn't seem so easy, I'd give that a go.

That depends on the belt tension, pulley diameter, belt wrap, belt and pulley material, and torque applied. Most clothes dryers use a stupidly thin (maybe 8mm or so) ribbed belt wrapped directly around the smooth drum. They hold fine with proper belt tension.

Matt

I'm trying chain the first go round, but a belt has a lot of appeal and I'd need to go with something like a 12" diameter to use a decent size drive pulley. Looking to push 5-7kw max power at around 500-600rpm at the wheel. Do you think a smooth driven pulley could work for that, or it is likely to slip and/or wear the belt prematurely?

 

[recumpence]

Hmm, 12 inches is a decent amount of surface.

I would say for a Neoprene belt, it would be worth a shot.

Matt

 

[bobc]

here's a picture of some gearbox housings I had waterjet cut in 20mm Al. The measured kerf taper is 0.07mm over 20mm thickness.
I dare say not all places are as good as they might be, the place in Macclesfield I used were very good.
You can laser steel up to 20mm+ but Al only up to 6mm or so - I think it just conducts heat away too well- that's why I say water jet and not laser.
I reckon if you made the overall diameter 0.1 or 0.2mm too big then just skimmed that bit off on the lathe you'd end up with a pulley that tracked fine.

 

[John in CR]

Hmm, 12 inches is a decent amount of surface.

I would say for a Neoprene belt, it would be worth a shot.

Matt

Thanks, I'll just be sure to start with a pulley that is sized right for teeth. Then I can mod it to either the epoxy mod, or maybe even easier, drill holes to run thin bolts through to make the teeth for a hybrid between Miles' lantern gear and a smooth pulley with which I could definitely skip teeth and no worries down the road of epoxy separation, which is a concern for me at 1krpm wheel speeds.

That brings up a question, what kind of surface prep are you guys with the epoxy/filler doing for a good mechanical bond? Epoxy doesn't like metal all that much.

 

[Miles]

Miles, I like the lantern gear rig, though I think I'd go double sided with the disk for almost no extra work.

For wider belts, I'd do something like this:

 

[Miles]

Same thing with skiptooth pattern.

 

[John in CR]

Miles,

With the lantern type, especially the skip tooth, without some curved support at the end of the belt's teeth, won't the belt try to make a straight line between each "rung" effectively changing the spacing, or is it not enough difference to worry about?

That, and of course simplicity in fabrication, is why I really like the idea of starting with a smooth pulley and using thin bolts or rod as the teeth right at the pulley's flat surface. Then the belt teeth still rest on the flat surface of the pulley and we can probably get away with skipping 3-4 teeth. Spacing and starting with the correct diameter pulley is still critical, but with the ability to skip most of the teeth, it could be even easier (and maybe better) than the epoxy method. Ideally we would want some odd number of teeth on the pulley, so the belt cycles through all of the teeth being engaged during multiple rotations for even belt and wear like should be done with fixed ration chain drives.

 

[Miles]

Miles,

With the lantern type, especially the skip tooth, without some curved support at the end of the belt's teeth, won't the belt try to make a straight line between each "rung" effectively changing the spacing, or is it not enough difference to worry about?

That, and of course simplicity in fabrication, is why I really like the idea of starting with a smooth pulley and using thin bolts or rod as the teeth right at the pulley's flat surface. Then the belt teeth still rest on the flat surface of the pulley and we can probably get away with skipping 3-4 teeth. Spacing and starting with the correct diameter pulley is still critical, but with the ability to skip most of the teeth, it could be even easier (and maybe better) than the epoxy method.

Localised bending reducing belt life was what I was worried about but you're right, if you miss out teeth it will affect the pitch but not otherwise. On the last two designs I posted, I modelled the pulley channel so that it supports the belt teeth (as you suggest).

 

[John in CR]

I'm glad Katou brought the topic up, because I wouldn't have thought of rods or bolts till you posted the lantern gear. With an AL pulley to easily drill, it may be the easiest route to a cheap sprocket.

 

[Whiplash]

Hey, couldn't you use this design on a typical v belt pulley? They are available with notches or teeth in them, maybe you could just match the pitch of the teeth and simply install the pins through the aluminum v belt pulley? Instant gratification! LOL!