Major mechanical problems....

[quickie25]

Hello all,

Well here it is less than a week befire the ship date and we have everything done and completed....until last night. Our robot will not move more than 10 feet without blowing the 40 amp fuse to the drill motors. We worked throughout the night to try and find the problem to no avail. After continual testing with our trusty voltmeter we gave up and summized that somewhere along the way we must have gotten metal inside the motors and this was causing the brushes to arc and short out the motor. So we replaced our standard kit drivetrain powered with two drill motors and the standard gearbox to the CIM motors in the same standard kit gearbox configuration. Now we have great power and sustained voltage as long as the bot is off of the ground, but the minute we put it on the groud, we blow fuses again.

Now assuming that our problem is that the motors are being ask for too much power and are blowing fuses, should we assume that the problem lies within the gearbox and the transfer of power between the output (motor) shaft and the wheel shaft and try the CIMS in a direct drive config without a gearbox?

Maybe we are overthinking things in trying to solve the problem.

We are very interested in any opinions that anyone has on possible problems/solutions. We have everything wired correctly and in working electrical order.

Any information/suggestions are greatly appreciated,

Sincerely,

Team 1380 - The Steel Dragons

[Tom Bottiglieri]

you could try lowering the voltage programmaticaly, or add lots and lots of cooling...

[quickie25]

Do you think its a voltage problem? We are only using two drivetrain motors and two window motors.

Thanks

[Dmitri]

I claim no expertise when dealing with motors, but you're going to be blowing fuses when the motor draws too much current, meaning when it's trying to handle a large load. Is your bot too heavy? Is the gear ratio okay? Friction problems?

[Tom Bottiglieri]

well how are youu driving? are you sure there is not too much friction on the wheels? does the main drive shaft drive freely when it is off the ground? what type of wheels/treads are you using?

[quickie25]

We dont have any problems whatsoever as long as the bot is off of the ground. We are using the standard wheelchair wheels in the back and caster in the front. Our bot weoghts about 75-80 pounds. We are also assuming that the motors are encountering either friction/resistance from somewhere and that is what is overloading the circuit.

One question that we do have is:

Are the CIM motors as good as the drill motors? We seem to get much more power out of the CIMs that we did the drills, but that all depends on the gearbox, of course. We plan to continue with the CIMs as long as we can track down the fuse problem.

Thanks

Team 1380

[Ryan Albright]

the cims are reliable they have been our drivetrain motors for the past 3 years, but the drills our also good well really depends how much torque and speed you want

[Tom Bottiglieri]

are you running the CIM's into the drill motor gearbox?! This will give a speed that is insanely high and far less torque

[Rickertsen2]

can you give a more exact description of your drivetrain? What gear ratios do you have? What are you using to acheive these gear ratios? Is there any misalignment anywhere? Your explanation is a little confusing?

Oh and btw to answer your question about drills vs. chips, they both have their place. The drills are i believe slightly more powerful than the chips. The drills have a much higher free speed and a much lower torque output. The chips have much higher torque and much lower speed. The CIMs are much more reliable and durable than the drills.

[quickie25]

I do apologize for my lack of knowledge in the subject area, but as I mentioned we are a rookie team and are unexpereinced in these areas. We are using the standard gear boxes, the large gear amd the small gear and thats it. The lasgre gear is in on the output shaft and the smaller gear is on the wheel shaft. All of these came in our kit. We havent riiged any special gearings or customizations.

Thanks

[Ben Piecuch]

Originally Posted by quickie25

The lasgre gear is in on the output shaft and the smaller gear is on the wheel shaft. All of these came in our kit. We havent riiged any special gearings or customizations.

Thanks

Since there were no drawings of the Kit drivetrain this year, it's easy to have problems with the drive. I think your problem lies in your gears. You want to reduce the output speed of your motors using those 90 degree gears. But you've increased the speed by putting the larger gear on the drive, and the smaller gear on the wheel. Reverse the two gears (smaller on the drive, bigger on the wheel) and your problems should be solved. Hope this helps!

BEN

[Matt Leese]

Motors draw a lot of current because they are put under a high load. By pushing the motor's beyond 40 amps just by putting more stress on the motors, it would appear that there is too much load in your drive system. You may have some parts which are not able to move as freely as they would like to. You also may have problems with parts of your drive train being misaligned. Any of these issues can cause the motors to draw too much current.

As for my suggestion in solving the problem: put the robot up on blocks and run the drive train. Stress it. Watch how the drive train reacts. See if anything doesn't align. See if anything hits anything else. That will help you diagnose the problem.

Matt

[KenWittlief]

Originally Posted by Ben Piecuch

Since there were no drawings of the Kit drivetrain this year, it's easy to have problems with the drive. I think your problem lies in your gears. You want to reduce the output speed of your motors using those 90 degree gears. But you've increased the speed by putting the larger gear on the drive, and the smaller gear on the wheel. Reverse the two gears (smaller on the drive, bigger on the wheel) and your problems should be solved. Hope this helps!

BEN

YES YES YES!!!!

what Ben said!

you assembled the transmission backwards - the small gear MUST be on the motor shaft and the large gear on the wheel shaft

man! your wheels must be spinning a couple thousand RPMs when you have them off the floor!

also, it would be better to get the original drill motors and white gearheads in there instead - they are geard down lower than the Chips - and the FIRST transmission was designed for them.

If your motors were destroyed you can buy replacements, you can even buy complete Bosch drills at the hardware store and put them in tonight - it will cost you more, but dropdead date is only 3 days away.

[Kevin Sevcik]

Another thought. If the drivetrain was working ok with the drills, why don't you try testing the drills outside the robot and such? If you think it's a problem with the motors themselves, there are several atlanta teams. try to get in touch with them and borrow their drills if they're not using them.

If you're using the gears (they have diagonal teeth) with the CIMs, then they aren't being geared down enough to work. The CIMs look like they're designed to work using the sprockets, chains, and 6" wheels. If you want to use the CIMs you'll have to completely change out your drive system.

[quickie25]

We dont necessaryilt think of it as being the motors themeselves because the bot runs fine off of the ground with either motor. We were just trying to problem solve with the CIMs and we thought that we were well ont he way, untilwe put the bot back on the ground.