Chiaphua Gear Box

[Andy Baker]

I agree with Matt that it is a good rule of thumb to always contain your power transmission device (sprocket, gear, etc.) with two bearings on either side of the device.

This is a very conservative way to design. For instance, FIRST may (or may not) give us some new motors to deal with. Typically, teams have difficulty getting info on these motors. Ususally Dr. Joe or Paul Copioli finds specs on the motors during week 2 and the rest of us benefit. But, in the mean time, we gotta get designing.

Since we will probably know little about this motor and none of us will have experience using it, I will urge my team to put an extra bearing to support the end of the output shaft unless there is obviously no need to do so.

Now, as for CIM motors, I have seen many good designs which did not support the end of the shaft. As I have used these motors over the past 2 years, I have supported the shaft, being the conservative designer I am. It worked, but the CIM motor is probably better off without a supported shaft. Since the bushing holding the 8mm output shaft is long enough to support heavy side loads, supporting the output shaft with a bearing just adds an efficiency loss by introducing a slight bind in the shaft.

If FIRST gives us CIM motors again (and I hope they do), I'll not support the output shaft.

However, if FIRST gives us the same Drill motors as last year, I stick with supporting the output shaft. These motors are designed for an application where side loads are equalized in the planetary gearbox.

Andy B.

[Andy Brockway]

We have not supported the CIM motor based on the 2002 version. That one had an integral gear and included a cluster gear. Since the original application of the motor was unsupported than we felt our application was solid.

One word of caution - we still place the gear as close to the motor as possible. The farther from the bearing the larger the moment force. This goes for cantileverd wheels also. Place a bearing as close to the wheel as possible.

As for as the gearbox output shaft, we generally run a double sprocket with the chains pulling in opposite directions helping to balance the load on the shaft. With the low life of our robots (10 to 20 hours) you would probably not see any problems with side loading.

BTW, we did not support the the end of the drill motor in our shifting gearbox this past fall and do not plan on it for this next year. One of those engineering trade-offs. We may need to replace the motors at some point but I believe that they should last through two regionals, we will see