Drill Motors....OVERHEATING, DRIVETRAINS!

[Brian48216]

How are your drivetrains shaping up?

For some reason our drill motors are tripping the breakers really really badly. We don't seem to be able to get any torque out of the motors cuz once the robot stops on the ramp, it's next to impossible for it to start moving up again without tripping the breakers. The robot doesn't weigh all that much (we're at least 50lbs under limit)
And the motors seem completely unresponsive for the first few degrees of input from the joystick.

To add insult to injury...it's overheating.
There's a familiar smell of burning after a few minutes of run time.

Did I mention both motors had their brushes pop out?

[Jeff Waegelin]

Well, first off, are you using the 40A breakers or 30A breakers? The 40s will help, though it won't solve the cause of your problem.

Secondly, are you running the drills in high or low gear? It sounds like you're not getting enough torque to drive up the ramp. Switching to low gear, or adding additional gearing could remedy this problem. It'll mean a sacrifice in speed, but if you're popping breakers, it's probably a necessary thing.

As far as the unresponsiveness, the joysticks and Victors have a deadband right around 127 (center). Unless you use programming to scale your inputs and outputs, you'll have an area on the joystick that does nothing. There are a few threads about this (try a search) so I won't go into this too much.

Finally, the "smell of burning" means you're pushing your drills too hard and too long. Gearing will help this, but keep in mind, matches are only two minutes. The drills aren't designed for long time use, so try to avoid running your robot for extended periods. Give the motors a chance to cool off. It'll help a lot.

[Al Skierkiewicz]

Originally posted by Brian48216
How are your drivetrains shaping up?

For some reason our drill motors are tripping the breakers really really badly. We don't seem to be able to get any torque out of the motors cuz once the robot stops on the ramp, it's next to impossible for it to start moving up again without tripping the breakers. The robot doesn't weigh all that much (we're at least 50lbs under limit)
And the motors seem completely unresponsive for the first few degrees of input from the joystick.

To add insult to injury...it's overheating.
There's a familiar smell of burning after a few minutes of run time.

Did I mention both motors had their brushes pop out?
First, if you can't get any torque on the ramp, I would think your gear ratio is too low so the motor is running very low on the power curve, but then... You mention that both motors had their brushes popped out and I begin to wonder if the brush assy isn't damaged/misaligned causing some electrical problem. The most worrisome is the smell. I have always held this axiom..."If it smells burned, it is. If it is burned, replace it. If you don't replace it, it will fail when you need it and then thumb it's nose at you by sending smoke and flame in your direction."
BTW, what was your design speed and are you able to achieve that speed on a flat surface?

[Adam Y.]

Did I mention both motors had their brushes pop out?
Yeah errmmm using broken motors in the first place isn't helping your robot.:)

[Duke 13370]

We realized some time ago that the drive would cause problems like that, so we have all the output capped in software so the motors only go so fast. when we push the joystick full forward, the motor doesn't go full forward, it goes about 2/3 of the possible speed -- i think. We can change that easily to 3/4 or 4/5 when we start testing thoroughly.

[Gamer930]

Originally posted by Brian48216
For some reason our drill motors are tripping the breakers really really badly.

First make sure you have the 40 amp breakers.

Second try and switch the breakers with a new 40 amp breakers. I know we (team 930) got a defective breakers and we switched it with a new one and fixed the problem

[mav]

we had over heating on own test base but the actual robot we ran them for 10 minutes straight and they never even got warm

[jacob_dilles]

we were having overheating problems on the main drive motors, but we never blew any breakers as an experienced member of our team told us to stop when we smelt the burning... our solution was to mount 2 muffin fans into the motor guard, blowing right were the clutch meets the motor, inward. there is a built in fan at the end of the motor (where the power leads attach) that blows outward so our fans are just feeding the motor air. it works fine, we can drive up and down the ramp for 10 minutes and they only get warm... a little airflow can go along way... -Jacob

[f22flyboy]

official word from FIRST is that more than 1 muffin fan is illegal.

http://jive.ilearning.com/thread.jsp?forum=3&thread=1882&tstart=45&trange=15

we still have two on our bot, but if the inspectors say anything we can take one off with no problems

[Cory]

Thats not true, you cannot use two large muffin fans. You can use quite a few small muffin fans though, I think there were at least 4 in the kit.

Cory

[SuperDave]

team 987 is using the same drill motors and we are using go-kart wheels that give us a great ammount of traction. Your robot may have too much traction. running in high gear, our robot would over heat, draw too many amps, and reset. While running in low gear and 40A breakers, it ran fine, but not nearly as fast (duh). the fans inside the drill motors only spin when the motors are spinning. if you have any extra space and weight, i would reccomend placing fans near the motors. we dont have that luxury. good luck, thank mother nature for the extra 2 days - we needed it :-)

Prez, Team 987, Las Vegas, NV
Highest Rookie Seed, Einstein Division, 2002 Championships (5th seed)

[sevisehda]

Your almost certanly pushing the motors to hard by not gearing them down enough. Don't run motors full bore for long because you kill them. Keep in mind most of the parts for the bot are only intended to work in short bursts.

Get a can of air, flip it upside down and spray the motor. This should add half a minut. Metal motor brackets can double as a heatsinks.

[jzampier]

If you are serious about cooling the motors, make some small brackets with small fans on them blowing right over the brush assy. I would avoid the compressed air route as you might start shorting things when the ice thaws out.
( it will ice over ) You are trying to fix a fundamental design/fabrication flaw in 30 seconds and it won't work well.
Check the motor alignment too, if you are putting a side load on the motor ( as in, up, down, left or right on the shaft ) it will make the motor very unhappy and sometimes have results you describe.
If you are really cooking them that badly, might i suggest going down to 30amps instead of 40, if you are using 40 now, it might save your motors. Tripping a breaker for 5 seconds in a match is better than cooking a motor and being dead for a minute. ( in general ).

[Guyute]

the drill motors on our robot have overheated sooo bad that the plastic case they sit in is melting.

[Tonay K]

Two responses:

Our motors were tripping and stalling also, we solved it by doing the following:
1. Replacing one of our motors (the brishes fell out on ours too)
2. Replacing the Victor and 40-amp fuses connected to the motor

Also, I think that you can use two of the larger muffin fans (We did). We had the thorough technical inspectors come and check us out; they said nothing about having more than one fan being illegal.

[Gope]

A quick blast of "Cold Spray" should keep your breakers from tripping.

[LoganB]

Originally posted by Guyute
the drill motors on our robot have overheated sooo bad that the plastic case they sit in is melting.

You really might want to fix that with the little muffin fans and or using the large muffin fan to keep the fans cold.

[Al Skierkiewicz]

The rules still state only one large fan, unlimited small fans. Actually, this is the rule we are quoting...
C7
You must use 16 AWG or larger diameter wire to connect the window motors to the
Speed Controllers. You must also use 16 AWG or larger diameter wire from the
Circuit Breaker Panels to the Robot, large muffin fan, and any other connections to
and from the Relay Modules. The only exceptions are that 24 AWG wire may be
used to connect the small muffin fans and any LEDs to the outputs of a Relay
Module.
Since this rule uses the singular for the large "fan" and the plural for the small "fans" in reference the interpretation is one large fan only.
I always caution teams to use freeze spray sparingly, as shock cooling can cause some parts to crack and the spray can wash lubricant out of the bearings. Cold parts in a humid environment will also condense water on the surface, be sure to allow it to dry first.

[Andrew]

We're using a 4:1 planetary on our drill motor and feeding that into a 29:1 spur gear box. We have six inch wheels. This gives us a GR of 116:1 from the drill motor output to the wheel axle.

This gives us about a 4.1 feet per second top speed and about 1000 lbs of pushing power (barring slip of course). We have four motors in the drive system, so don't go trying to figure out how to get these numbers with just the two drill motors.

Since our second year (2001), we have used a big, achin' aluminum tube heat sink surrounding the motor with small muffin fans constantly forcing air through and across the motor.

We have not (knock on wood) experienced any over-heating with our system and we have pushed it pretty hard.

We had two years (2000, 2002) where we used a much higher gear ratio. I don't have the numbers in front of me, so I cannot give them to you, but figure at least 2x the above GR. In those years, we popped circuit breakers when we really ran our robot roughly.

There are issues of gear box efficiency that factor into this mix. If your GR is comparable to the one I quoted, but you still have these problems, you might discover that you are losing a lot of energy in your gearbox and therefore increasing the current your motor draws in order to run at the above torque/speed point.

There may also be issues with how your drive system is laid out. If you are using differential rear wheels and casters, you will have some difficulties with maneuvering on the hill. You have to use a lot of torque when you correct to go straight on the hill, because your system will not naturally resist turning.

I don't know what you can do at this point. If you have sprockets driving your output, you might be able to put a big sprocket on your wheels and keep motoring.

[camtunkpa]

THERE IS AN EASY AND LOGICAL SOLUTION!!!

The motors are getting too hot and popping breakers simply because your gear ratio is not low enough. This is also causing the dead band when you move the stick. To correct the problem first try switching the gearboxes to low range, if they are already in low range then decrease the size of the gear on the motor and/or increase the size of the gear on the output shaft. I highly doubt it is a problem with the brushes because he had our assembly pop, but they were still working fine. I suggest this is not a problem with the motors or electronics, but a problem with the gearing. Since you tripped the breakers repeatedly (I am guessing) I would also suggest replacing them after solving your gear ratio problem. Good luck and if you ever need any advice, call on 222.




P.S. another tip is instead of using the plastic mounts provided, make your own aluminum ones, not only will they be stronger, but they will dissipate heat.