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Unread 01-06-2011, 21:34
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Eric Scardelli
AKA: Eric S
FRC #0075 (RoboRaiders)
Team Role: CAD
 
Join Date: May 2010
Rookie Year: 2009
Location: Hillsborough, NJ
Posts: 9
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Re: Custom gearboxes

If you're interested in making your own custom gearboxes, it would help to have access to two machines:

-Lathe (For shafts)
-Mill/CNC (For side plates/ facing-off gears)

A gearbox is simple: Side plates, stand offs, bearings, shafts, spacers, gears, and keyways/keys.

A good place to buy quality gears would be Martin Sprocket. You can use either hardened steel gears from that manufacturer or 7075 aluminum gears (from a different source). It is safe to go with 24 DP, but I believe some people have had success with 28 DP.

Stand offs you can get from McMaster-Carr as well as keystock for keys. You can make aluminum side plates from 3/16 6061 alum. or steel 1/16 sheet metal (we don't use sheet metal).

Autodesk Inventor makes it fairly easy to design gearboxes, if you are serious about making them CAD is the place to start. Inventor has gear generators, key/keyway generators, and bolted connection. If you input the right numbers into it it'll calculate the ratio and it will also tell you if the gearbox will fail or not.

Gearboxes are harder to make the smaller they are but it's not a matter of design it's more of where to get the parts; tiny bearings are easy to find but working with such small shafts and gears may be difficult. It is not impossible to create a custom planetary gearbox but it is a challenge.

When making your gearbox always pick your gear ratio based on the motor curve- look at the point where torque and speed are balanced and decide where to go from there. Perhaps for and arm you need torque but a gripper may need speed. That's probably the first step to determining how you design.

Hope this helps.

-Eric