New Bosch Motors desoldered?

[Clark Gilbert]

Some teams have reported that the brush assy is easily broken and FIRST is recommending that teams DO NOT solder new wires to the motors as the brush assy is plastic and easily melted. Is it possible that brush assy was damaged before this incident and the brushes were actually shorting? Please let us know what you found.

Our lead electrical engineer tried it today on one of our 3 busted drill motors. He desoldered the old wires and took them off. Then he used one of those connectors after he cut the plastic end off. He slipped that over the drill motor part, and soldered the connector to the motor (only heating it on one side). It works really well and didnt melt the surrouding plastic or damage the motor.

http://www.theforumisdown.com/upload...0103/motor.JPG

copy and paste that link for it to work

[jzampier]

Our team kinda decided we knew better than
FIRST on this one. We did desoldier the wires
and resolder 10 gauge on there, but the
flexiblity of the brushes and mounting
gave us a lot of trouble with broken solder joints. Final solution was to use 2-56 screws
with some non-insulated 10 gauge crimp terminals ( male ) and literally bolt the connectors together. ( did need to drill out the
holes on the motor terminals ).
As a side note, you have to make sure you
don't bend the motor brush housings, they
held the solder temps fine, but i managed to
break off the brush retaining tab when
rotating the terminal to the correct orientation.
If you ask me these motors have a terrible brush retention mechanism and it should be
fixed. I was temped to electrical tape the heck out of it when i was done... but i was afraid to
kill the air flow over the stator, amongst other things.

[Dick Linn]

There are several possible reasons for a "melt down" Perhaps the initial solder joint was "cold" or the joint/wire was damaged in handling. Perhaps a few strands were broken in handling. Increasing the resistance at this point would cause the joint to heat up.

More importantly, running at or near stall current will really cause things to heat up! (I used to sell a precision current calibrator that could put out 100 Amps continuously and it could melt contacts and wires far bigger than what we are dealing with here if the connection was not perfect.) Worse, you will destroy the motors if you are not careful. Treat these babies gently if you want to have a reliable robot.

I agree with all that the plastic brush holder and etc. in the motor is extremely fragile...one of ours's has a hairline crack already. Be careful of how you mount the motor if you use the brackets in the kit! And don't drop one.

[Al Skierkiewicz]

Originally posted by jzampier
Final solution was to use 2-56 screws with some non-insulated 10 gauge crimp terminals ( male ) and literally bolt the connectors together. ( did need to drill out the holes on the motor terminals ).

This is a good solution if you have already unsoldered the original wires. I would recommend a star washer be placed between the motor terminal and the wire terminal when assembling. The star washer will prevent the two parts from moving against each other and eventually loosening the joint. Additionally, it will insure that there is a firm electrical contact between the parts.
I would remind everyone, when looking at Clark's picture, that soldering to this assembly as shown requires expertise beyond most teams. The engineer who performed this operation has demonstrated his talent with the use of a soldering iron and his knowledge of delicate soldering techniques. My hat is off to him.

[Trashed20]

we got our robot running last night and when we showed up today one of the wires on one of the motors became desoldered. Is there any way to attach this back on without soldering? Do we just need to order another motor? Are there any motors we can get by next week before shipment?

[Adam Krajewski]

We've had several problems with the drill motors.

The first incident was caused by the interaction between a motor lead and a polishing wheel. The result was a motor flying across the shop and a broken plastic brush assembly.

The second incident was caused by running the drivetrain for much too long, de-soldering one of the leads. I was not there to verify the validity of the claim, but I did see the botched "repair" job.

I eventually found a way to solder 10GA. leads AND avoid melting the plastic brush assembly.

In comparing the broken motor with a new one I noticed that the brushes are held by the assembly in three places (using Clark's picture as a reference): In the center between where the leads are attached and the braided copper wire via a small retaining nub, on the left via a slot with no retention, and on the right by another small retaining nub.

I was able to VERY CAREFULLY (as this assembly is quite fragile) push the brush in, down, and twist slightly clockwise on the left(using Clark's picture as a reference once again) to remove it from the motor.

With the brush safely removed from the motor, I was free to solder away. I use a technique I learned back in ’99 (from the Baxter Bomb Squad, if I remember right) and have used ever since for all drill and fisher price motors. I first tin the wire and connector tab and solder them together. Then I wrap the wire and connector tab with solid core 24GA. copper hook-up wire from end to end and coat the connection with more solder for a very solid hold. Finally, I shrink wrap the entire connection.

The brushes, once cool, can then be CAREFULLY slid back into the plastic assembly by lining up the left side with its channel and popping it back past the retaining nubs.

For broken assemblies, we've simply band-tied the brushes in place with much success.

We have not noticed any decrease in performance due to these modifications versus brand new motors with crimped connectors to the 16GA. leads.

Do this at your own risk with new motors, but you may be able to salvage broken motors this way.

I can take some pictures of the finished mounting if anyone is interested.

Adam

[WizardOfAz]

We are using last year's bot for new driver practice and programmer practice with the new RC. But one of the drill motors blew its brushes to bits after a few minutes of driving this fall. I'm glad it made it through the competition last year.

So we've ordered a replacement motor and some spares, but it's a shame to toss a motor for lack of $1 worth of brush and assembly. Has anyone found a source for these parts? B-S says no-can-do.

Thanks - Bill

[sanddrag]

Originally posted by WizardOfAz
We are using last year's bot for new driver practice and programmer practice with the new RC. But one of the drill motors blew its brushes to bits after a few minutes of driving this fall. I'm glad it made it through the competition last year.

So we've ordered a replacement motor and some spares, but it's a shame to toss a motor for lack of $1 worth of brush and assembly. Has anyone found a source for these parts? B-S says no-can-do.

Thanks - Bill

My local ACE hardware store sells power tool brushes but it is just the brush, not the whole endbell assembly. I do know where to get the motor for $24.

[WizardOfAz]

OK, give it up, where?

[sanddrag]

Originally posted by WizardOfAz
OK, give it up, where?

Oh alright. Here link