Drill motor suggestions...

[team222badbrad]

We have had several problems with the drills...

Here is what you should be alert about....

1. They motor mounts easily break-Machine your own if possible or order several mounts.

2. Keep an eye on the brushes- be careful not to push them into the fan blades or you will have broken fans.

3. The gearboxes easily pop apart when they have lots torque on them-make your own motor mounts.

4. The brushes also easily pop out-you need to find a good way to hold them in good.

If you have had any other problems please tell everyone so they know...

[Joe Johnson]

Has anyone else seen these problems?

As to pushing brushes into fan blades and having them easily pop out, how is this possible? What are you doing to the brushes? I find it hard to believe that the motor brushes will pop out at all yet alone easily. Please explain. Also, please upload pictures of your set up I am very curious (and nervous).

If anyone else is having these types of failures, please tell us all.

For my own part, I am making sure I am supporting the front end of the motor shaft independent of the plastic holding pieces that FIRST provided. I just didn't have a good feeling about the ability of the set up as it was to support any side loading whatsoever on the end of the drill shaft.

Reports from the field are welcome.

Joe J.

[Moshingkow]

The first day we finished our drivetrain, we had these problems. the motor mount closest to the end of the actual motor broke in 3 places (epoxy is currently drying on it). The rear of the motor has a plastic piece that holds the brushes in. one of them completely broke off, and we were holding it on with electrical tape. no good. it completely broke off. The motor is pretty much useless, unless we can find a way to keep the brushes secure.

I think we may try and machine a motor mount out of aluminum and reinforce the back of the motor with epoxy or polyester resin. theres really not much you can do for the rear of the motor.

Tenkai

[ReggieB]

Our team also had problems with the rear support hitting and breaking the fan inside the motor. We almost broke one of the black plastic pieces, and are currently worried about the output shaft. It seems to wobble a bit, we ran it mouted on a board at high speeds and carefully watched it. We are sure that the motor itself was stationary, as was the gear box. Any suggestions on how to fix this?

we already had a damaged drill motor after someone dropped it. The clip holding the brushes in popped off so now the brushes are loose. We held them in using twist ties and locking them into the motormounts. I recommend putting your motormounts into a place that is protected by your drive chassis. As for the plastic/rubber connection to the drive shaft, I think that's supposed to wobble and have some give in it so when you run the robot, it can afford some flexing instead of breaking completely.

[Dodd]

badbrad, Moshingkow, and ReggieB,

Are the locking pins IN or OUT of your gearboxes?

I have not personally looked at this year's drill motor and gearbox, nor the FIRST provided mounts. My comments are based only on 6 year's experience with the units provided in last year's kit.

I think that leaving the pins in is extremely risky, and an invitation to breakage. When the driver backs off the stick with the robot at speed and its momentum overruns the drill transmission output shaft, the shaft locks to the transmission housing. Whatever mounts the housing to the frame is immediately shock loaded with a torque equal to the torqe it takes to spin your wheels.

Shock loading sucks. It's a leading cause of mechanical failure. The people who developed the transmission, with its locking pins, developed them to take the torque loading involved when you tighten or loosen a drill bit in a keyless chuck, while you hold the chuck by hand. A product that never fails when operated in that mode can't be expected to absorb the kind of shock loading produced by a FIRST bot drive without failures.

BTW, this problem is most severe if the transmission is run in low range with direct drive. If there is a stage of gear or chain reduction between the transmission and the wheels, that reduces the magnitude of the shock loading by the gear ratio.

I think the teams who counsel leaving the pins in for their braking effect have used drive train designs and control strategies in the past that mitigate the shock loading problem sufficiently to escape damage. They have been lucky.

So do tell, gents. Are you running pins IN or pins OUT while observing these problems you are describing?

Dodd