What's a good transmission these days?

[Greg Needel]

Ok here is my thing about a cvt. most people who know me know that I have been sitting on an original design for a while now and I tried to create it at one point and failed. But this was not all a loss in the process of making it I found a bunch of problems with both the manufacturing and the concept.

Here are some of the problems with a cvt

1) Weight. Since they have to be solid metal they are going to be very heavy, and if you decide to use to that is twice the weight

2) cvt's are not efficient at transferring torque. because they are not a firm connection between the there will be a lot of slipping, which is fine for their original application (snowmobiles, and other gas engines)

3) the gear ratio's are infinite but only to a point. lets say you have 2 identical cones 3 inches on 1 side and 1 inch on the other the max ratio you can have is 3:1 and 1:3 and if you want this smaller then 6 inches it is a serious taper angle (hard/impossible to machine without cnc, most lathes have up to a 15 degree taper angle) so now that you have this short really severe taper with 1/4 inch chain and the movements would be small but the ratios are not worth it.


In my opinion you would be better off making a 2 speed shift on the fly tranny because they are simpler to build with less variation, they also have a better torque conversion and can give you any desired gear ratio (From design).




as for other gear boxes which is best this is a tricky subject with out knowledge of next years game. 2 speed tyrannies are good over all but have issues like weight and a lot of machining.

single speed tyrannies are good but you need to figure out for sure what you want by analyzing the game and figuring out what is more important speed or power.

then the last most common choice is chain gears, personally I like this method because of its simplicity. and you can change the gears easy if you want to change the ratio during the comp (trust me I have done this many times) it also allows you to focus on more important things on your robot like functionality.

I hope this helps and if you decide you would like more information on anything feel free to pm me



edited to say: there are many types of cvts and in this post i am refering to a cone cvt a mentioned in the thread starting post. the thunder chickens used a planetary gear cvt, wpi used a friction taper cone, and there are many others.