Sprocket calculations

[Gourav]

How do people find out fos of rear sprocket? Analytically?? FEA??
The problem is that MD books dont talk of sprockets too much....& in FEA, i dont know how to apply the loads? One of the forums i read talks of doing FEA on simple disc instead of toothed one but I am not very sure about how accurate the results would be.
Pls post soon...I am stuck on this.

[Hector]

If you want to try a semi-accurate representation of the loads on the individual teeth of a sprocket, draw a free body diagram of the forces acting on a single link. Start at the first link to touch the sprocket. There are three forces: chain tension from engine, chain tension going to next link in chain, and reaction at the tooth. If you can figure out the pressure angle of the tooth/link contact than the equations come out quite nicely. Now this isn't terribly accurate because strain in the chain and teeth cause the load to be more evenly distributed but it's a starting point.

Alternatively, just buy a sprocket from someone like Sprocket Specialists and you're done. They're relatively light and not too expensive.

[RollingCamel]

The "Cool" thing is to be able to manage and make the system work. Don't waste time on trivial issues, its not a design course exam.

If it is your first year then chassis, suspension, upright and hub, intake and exhaust, cooling and lubrication circuits are your main issues. Just to make the car move..

Anyway, this is what 1st year for to know what is what.

[Jipy]

I did our team's sprockets last year using FEA. I used what is called distributed loading which is pretty realistic (kind of what Hector said). With geometry, you can compute the load on each engaged tooth. The first one of course takes a beating but then the load decreases down to the last engaged tooth. We ended up with pretty lightweight sprockets. I still don't quite understand how such a small amount of material can transmit 80HP!

If you can't work out the maths, just let me know and I'll try to find my calculations. Don't go with a straight disc, you'll end up far from reality.

[Demon Of Speed]

First off, there of plenty of sprocket manufactures out there using steel and aluminium. This should tell you that the teeth can withstand the force directly applied the the sprocket. (if you don't feel comfortable making this assumption then do the hand calculations.

I would recommend doing a solids analysis on the sprocket. If done in a spread sheet you can find the minimum material thickness at different radii. The thickness will be quite small.

Using a "disk" to determine how much material can be removed works just fine. Remember to apply the moment only where the chain is rapped (you should have chain rap calculations already done). Then fix the bolt holes in the FEA. Remove what material you think you can. Iterate the design until you feel it is optimized enough.

[PBR-Simon]

page 105 of 'Standard Handbook of Chains' has the equations you're looking for. A pdf shouldn't be to hard to find either.

[Spetsnazos]

There are a few books on this matter but most Machine Design books would have this for you. As the 1st reply states, you have to look at the force associated from the engine torgue, chain tension and the number of teeth engaged.

[Wesley]

Don't neglect impact loading. It's not inconsiderable, especially if you have drivers that like power-on shifts, high-RPM clutch dumps, or if you have to push start your car a lot.

You'd be surprised what kind of impact loading a 14k RPM clutch dump can put on a chain and sprocket. This will also have a big impact on your sprocket fatigue life. In fact, I'd say engine torque is negligible compared to the impact loadings you will see. Almost every drivetrain failure I've seen can be traced to improper calculation of impact loads and fatigue limits.

[nvpF1crazy]

By impact loads you mean the starting and braking chain tension right? How are they calculated?