pic: 3CIM Ball Shifter

[Aren_Hill]

Originally Posted by cad321

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Quick bit of advice, it is probably good form (on both the ball shifter and dog gear setups), to put your third reduction after the shifting shaft.

This method can be seen on the Ball Shifter with optional 3rd stage, and the AndyMark Sonic/Super Shifters.

This lowers the overall torque being transferred by the shifting components, which results in less chance of failure and lower required shifting forces.
See this thread for once instance of failure: http://www.chiefdelphi.com/forums/sh...ght=20+carnage

Doing this would also allow you to make your gearbox overall shorter as you can offset the last output shaft in whichever direction you like.

[Lil' Lavery]

I have another question. Why bother with a 6-CIM, 2-speed drivetrain at all? It seems like a lot of resources to invest in only marginal gains over either a 4-CIM, 2-speed or 6-CIM single speed.

[Karthik]

Originally Posted by Lil' Lavery

I have another question. Why bother with a 6-CIM, 2-speed drivetrain at all? It seems like a lot of resources to invest in only marginal gains over either a 4-CIM, 2-speed or 6-CIM single speed.

Something very important that also needs to be considered is what is the opportunity cost of those two extra CIMs. The concept of opportunity cost is invaluable in making effective strategic designs decisions, especially when it comes to resource allocation.

Here's a Kahn Academy lesson that does a great job of explaining opportunity cost. A bit more detailed than is needed for these purposes, especially in terms of the PPF, but hey at worst you're going to learn some extra stuff.

https://www.khanacademy.org/science/...?v=pkEiHZAtoro

[Cory]

Originally Posted by Lil' Lavery

I have another question. Why bother with a 6-CIM, 2-speed drivetrain at all? It seems like a lot of resources to invest in only marginal gains over either a 4-CIM, 2-speed or 6-CIM single speed.

For us it came down to the fact that we wanted to utilize our drive motors to hang (we set our initial goal at less than 10s) and we also wanted to maintain the responsiveness and acceleration of our 2011 robot, except 30 lbs heavier. To do that we needed the extra CIMs.

[Gregor]

Originally Posted by Cory

For us it came down to the fact that we wanted to utilize our drive motors to hang (we set our initial goal at less than 10s)...

PTO's are an entire different ballgame, and negate some (most?) of the issues Karthik was trying to bring to light with looking at the opportunity cost.

[Tom Ore]

Originally Posted by Aren_Hill

Quick bit of advice, it is probably good form (on both the ball shifter and dog gear setups), to put your third reduction after the shifting shaft.

To generalize what Aren is saying, always try to put your mechanical advantage as close to where you need it as possible. (That is, pass the big forces or big torques through as few components as possible.)

[MichaelBick]

I agree that 6 CIMs are overkill if you aren't using a PTO. 4 CIMs + 2 550s seems like a good compromise and additionally makes it harder to blow the main breaker(our 6 motor drive was geared for 19.2 FPS @ 100% efficiency and never blew the main breaker). I agree with karthik though: if you can't find an easy way to add the extra motors, it isn't really worth the effort of completely repackaging the gearbox.