Major mechanical problems....
 

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

Re: Major mechanical problems....
 

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

Re: Major mechanical problems....
 

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

Thanks

Re: Major mechanical problems....
 

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?

Re: Major mechanical problems....
 

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?

Re: Major mechanical problems....
 

There are lots of factors involved that may affect your drive. Here is a thread that addresses several possible causes:

http://www.chiefdelphi.com/forums/sh...ad.php?t=25589

If you have any specific question be sure to ask some of the respondees to this thread like Al and Joe. They have lots of experience and are good about giving responses that might help.

Re: Major mechanical problems....
 

direct drive from the CIMs is definitely not going to work, they don't have enough torque straight out. What would really help is a description of your drivetrain. What gearing are you using? What size wheels? Are you sure there isn't any binding in the drivetrain somewhere?

That was my first assumption about what was wrong with your drill motor drivetrain, as metal shavings shorting the motor would mostly completely kill it, not kill it after 10 feet.

Re: Major mechanical problems....
 

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

Re: Major mechanical problems....
 

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

Re: Major mechanical problems....
 

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

Re: Major mechanical problems....
 

We are using the standard gearbox configuration that is included in the kit. Since we are a rookie team, we started with what we had. I am afraid that we may have a little binding within the frame. I have attached a picture from about three weeks ago so you can see the setup.

Thanks

Re: Major mechanical problems....
 

What do you mean by power? The CIMs and drills are pretty much equal in power. If you're talking about how fast the wheels turn, that could be the entire problem. The CIMs free speed is 5500 rpm. if you guesstimate 2500 under load driving your robot, and the 12.5" wheels, then you need atleast a 10:1 gear reduction for them to be able to push your robot.

Edit:
Tomman has a good question. are you running the CIMs straight into that gearbox? if so, they won't provide nearly enough torque as that is only a 2:1 reduction.

Re: Major mechanical problems....
 

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.

Re: Major mechanical problems....
 

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

Re: Major mechanical problems....
 

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.