Blowing drill motors

FIRST General Forum
1

Posted by nuts4first.

Engineer on team #340, GRR - Greater Rochester Robotics, from Churchville-Chili and Nortel Networks.

Posted on 2/22/2000 11:30 AM MST

During practice runs these past few days, we have managed to blow 2 drill motors. The armature breaks right off at the bend. Two well experienced teams in our area have also blow the same motors. I’m suspecting a motor quality issue here!!! Is anyone else blowing these motors as often?

A few details on the drive system…we are using a pillow block, we have used an amp meter to check that the motors are aligned & not binding, the program has a ‘dead zone’ for neutral joystick position and the speed controls are calibrated.

Thanks,
Team 340.

2

Posted by Nate Smith.

Other on team #66, GM Powertrain/Willow Run HS, from Eastern Michigan University and GM Powertrain.

Posted on 2/22/2000 11:44 AM MST

In Reply to: Blowing drill motors posted by nuts4first on 2/22/2000 11:30 AM MST:

We’ve had a little trouble with ours getting hot and that’s about it…if the shafts are breaking, I’d double check your side loads…

Nate

3

Posted by S. Krussell.

Coach on team #349, Robahamas, from International Academy and Ford Motor Co…

Posted on 2/22/2000 5:44 PM MST

In Reply to: Re: Blowing drill motors posted by Nate Smith on 2/22/2000 11:44 AM MST:

We did not blow a drill motor, but they have become warm a few times. We did, however, blow the speed controller on one of the drill motors, plus the spike relay. We are a little concerned about the drill motors. I hope we can trust them to endure.

4

Posted by Joe Johnson.   [PICTURE: SAME | NEW | HELP]

Engineer on team #47, Chief Delphi, from Pontiac Central High School and Delphi Automotive Systems.

Posted on 2/22/2000 7:33 PM MST

In Reply to: Re: Blowing drill motors posted by S. Krussell on 2/22/2000 5:44 PM MST:

In my opinion you have to be pretty abusive before the drill motors give you any grief at all.

The motors can get VERY hot before they have any serious problems (unlike the Fisher Price motors which seem to melt fans if they even THINK about putting in a hard day’s work :wink:

Yes, I know that output suffers when they get hot. Yes I know that over the long term abuse kills even the room temp. performance. But honestly, I can only think of one or two in 5 years that just flat out died on us. Not a bad record considering the abuse we have given them (cool in a can and all).

As to the reliability of the transmissions that come with the motors… …I have much to say about that…

…it will keep for another day.

Joe J.

5

Posted by nuts4first.

Engineer on team #340, GRR - Greater Rochester Robotics, from Churchville-Chili and Nortel Networks.

Posted on 2/23/2000 1:27 PM MST

In Reply to: Drill Motors are pretty tough… posted by Joe Johnson on 2/22/2000 7:33 PM MST:

Is a 15 (on the drill axle) to 18 (on the wheel) gear ratio bad? We are locked in low gear and driving 2-6’ wheels with each motor. Our robot weights 130 lbs. I’ve tried to use some of the speadsheets, but I’m not sure now to read them.

What does everyone think?

-Team 340

6

Posted by Joe Johnson.   [PICTURE: SAME | NEW | HELP]

Engineer on team #47, Chief Delphi, from Pontiac Central High School and Delphi Automotive Systems.

Posted on 2/23/2000 2:32 PM MST

In Reply to: How is our gear ratio? posted by nuts4first on 2/23/2000 1:27 PM MST:

6 inch wheel, 70:1 ratio Should be okay. Fairly fast but not overly so, at least I don’t think so.

If you do a lot of spinning you will tire the motors fast but other than that you should be okay, assuming that you have good bearings for your drive shafts & the chain routing is okay & etc.

Joe J.

7

Posted by Dodd Stacy.

Engineer on team #95, Lebanon Robotics Team, from Lebanon High School and CRREL/CREARE.

Posted on 2/24/2000 8:56 AM MST

In Reply to: How is our gear ratio? posted by nuts4first on 2/23/2000 1:27 PM MST:

: Is a 15 (on the drill axle) to 18 (on the wheel) gear ratio bad? We are locked in low gear and driving 2-6’ wheels with each motor. Our robot weights 130 lbs. I’ve tried to use some of the speadsheets, but I’m not sure now to read them.

: What does everyone think?

: -Team 340

Nuts,

This is gentle gearing in terms of loading the drill motors and heating them up. Your top speed is probably about 6.3 ft/sec. We have in the past run direct drive (1:1) in LO range to the 6’ wheels, 7.6 ft/sec top speed, with no problems.

A suggestion to consider, tho, is to run the drill gearbox in HI range and take a larger, compensating, ratio reduction in the final chain and sprocket stage, netting (nearly) the same overall gearing. This reduces the maximum torque transmitted by the gearbox and any joints in or to the output shaft (like your 15 tooth sprocket), reduces the reaction torque that the drill housing and its mounts need to absorb, and reduces the tension in the chain. And I mean reduces by a factor of 3+.

With all the front/back maneuvering these bots do at max acceleration, it really works the whole system thru a lot of stress reversal cycles. I’ll take a factor of 3 load reduction any time, but that’s just my opinion. Some folks love tearing down gearboxes, drifting out snapped pins, and fussing with master links in the calm, well-lighted pits. I would also wager that the chain/sprocket reduction stage has a better mechanical efficiency than the plastic planetary stage in the gearbox that is eliminated in this approach.

A 40 T (3/8’ pitch) sprocket can fit your 6’ wheel (4.78’ pitch dia.), and paired with a 10 T drive sprocket and the drill gearbox run in HI, would give you a 6.0 ft/sec top speed vs your present 6.3 ft/sec. A 12 T drive sprocket nets about 7.2 ft/sec. This is working with sprocket availability from SPI - you can probably find a finer mesh of ratios available thru other suppliers, but this is a pretty minor speed range as is. Good luck.

Dodd