How long do aluminum cogged belt drive sprockets last?

[John in CR]

How long do these hold up. I've come up with a really simple way to install a drive sprocket, but it would be permanent. The center hole needs to be over 2" so I'm talking about a fairly large sprocket. Do they last long enough that wear is a non-issue? If power and rpm make a difference in the answer, let's say 15kw peak at a max of 2500rpm.

John

 

[liveforphysics]

I've never seen one wear out yet. A Zero with 15,000miles on it just has the surface looking a bit more polished than new, but no measurable signs of wear.

I would imagine if you regularly rode through deep sand or something you could accelerate the wear, but I would call it a life-time part for regular ebike duties.

 

[John in CR]

Great. That's good enough for me. It will be a perfect test of Doc's magic epoxy with the only real risk being if the sprocket breaks loose pulling out in front of a car. Spinning motor cover on one side and inside the sprocket, and swingarm on the other side should make a failure a non-event. An hour of 49°gives it a full cure, so a simple solar oven for curing can't hurt the motor or wiring. Over 6sqin of bonded surface area with the load at over a 1" radius should make it a good application for the stuff, and a super simple sprocket attachment once I get the center hole done.

What do you think, a couple of grub screws as insurance or just go for it?

 

[bigmoose]

Luke, if my memory is correct, remember those guys that hard coat anodized the VTEC cam pully's and the wear was negligible? That may be the ticket for you John for maximum life.

 

[John in CR]

Below is the motor in question. That part houses the bearing, and the material is just over 5mm thick. I'll use the motor as a lathe for itself and cut it flat as I drew with the white line to center the pulley. Turn the pulley out to that diameter as well as try to duplicate the taper of the cover. Make sure both surfaces are well prepared (use only water as my coolant during the machining, so no worries about oil afterward. Slather on some DP420, clamp it on. Spin it up after initial room temp cure to make sure I didn't get the pulley off plane. Then solar oven cure it for a couple of hours.

What do you guys think? The motor cover is cast steel, but I take it that the epoxy is enough protection between the AL pulley and the steel.

 

[Hillhater]

john,
if you have 5mm of steel to play with on that hub, i think you may regret not putting a shallow key way in there ( 2mm deep x 6mm wide ?) , ..Or a "pegged" key may be easier......with a corresponding 4mm deep x 6mm wide key in the pulley.
DP420 is good , but double insurance is comforting ..(for when you are pulling out infront of that car :wink: )

A pegged key

 

[liveforphysics]

I would try to drill a couple shallow holes (3-4mm or whatever you have for material thickness without breaking through), then fit a pin or two in there, and file a corasponding slot into the ID of the pulley so it sits over the pin bores. Then apply good epoxy to the mating surfaces, and apply a firm torque in the made for load direction so it cocks the pins in the bores and loads them in shear while the epoxy cures.

It would really be ideal to be able to get a few fasteners into that cover as well, even if it's only 2mm thick or whatever, you could still drill and tap holes for like 20 little m3 size screws or something that would help with shear load and clamp force.

 

[John in CR]

The inability to put holes in the sides was why I want to go the epoxy route. Now that I already cut the axle on this one, the stator will be extremely difficult to get out. 2-4 grub screws is something I planned. A keyway seems great if you have a way to machine it. Don't forget the over 1" radius. On a 0.5"-1.0", I'd be all over some kind of splines or keyway on the "shaft", but at this radius some grub screws and strong epoxy should be fine. If the grub screws aren't pretty much just unnecessary insurance in this implementation, then we should be yelling from the rooftops warning of the insanity of glued on torque arms.

 

[hydro-one]

i cant wait to see this!!

 

[Danny Mayes]

Hey John,

For what is is worth I use loctite 6xx retaining compound. it is insanly strong, cures at room temp and can be released with heat. I have pulled a boss of a motor shaft that i guled on with this by heating it up whist the motor was in wet rags with very little heat going into the motor. This would be strong enough to not require any added mechanical locking. You seem set on the epoxy but thought i would throw in my 2c.

http://thirdshift.nu/portfolio/v3/pdf/mro_catalog.pdf

D

 

[John in CR]

Hey John,

For what is is worth I use loctite 6xx retaining compound. it is insanly strong, cures at room temp and can be released with heat. I have pulled a boss of a motor shaft that i guled on with this by heating it up whist the motor was in wet rags with very little heat going into the motor. This would be strong enough to not require any added mechanical locking. You seem set on the epoxy but thought i would throw in my 2c.

http://thirdshift.nu/portfolio/v3/pdf/mro_catalog.pdf

D

I've heard that loctite has some really strong stuff, and some of them approach the shear strength of the DP420, which I've been unable to find down here. Loctite should be easier to find, and since it's designed specifically for metal, it may be better. The 680 looks like just the ticket. Thx for pointing me in that direction. As much as any adhesive just seems wrong, this is a perfect opportunity to give one a chance. I never use max thrust crossing in front of cars, so if it did fail, the worst result is likely to be only pedaling home.

John

 

[Danny Mayes]

Hey John.

Glad to hear it helps.

You can work out your factor of safety by calculating the bonding surface are in square mm and using the value loctite give as the bond strength. I am not that good with maths to do it for you. I think you will have to convert the torque to a sheer force. When I glued my pulley to my wheel I did the calcs inside of a modeling program and it has a FOS of over a hundred. Knowing your FOS might give you some peace of mind. I think you will find it is quite high.

D

 

[Punx0r]

You certainly can

The glued area will give you the polar second moment of area (J in m^4), throw in the applied torque (T in Nm) and the radius (r in m) of the contact patch (as the max shear stress is at the outer most edge) and you have shear stress (torr, in N/m^2).

T/J = torr/r

So

torr = Tr/J

It's a big help if your contact patch is circular :lol: If so, J = (pi x D^4) / 32

D in metres

Hope this helps!