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.

Re: Major mechanical problems....
 

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.

Re: Major mechanical problems....
 

next chance you get, run the motors with the bot off the ground. if you can stop the wheel from turning with one hand, then it's not putting out enough torque

Re: Major mechanical problems....
 

We just tried that and we blew the fuse again. The whole things runs like mad until its put under stress. Based on the past posts, I think that we have a serious problem. We are going to dissasemble our gearboxes and check the driveshaft opening through the frame for any friction that may be occurring. If that doesnt solve the problem then we may drop the current drivedtrain altogether and create a direct drive system with sprockets and chains.

Thanks for the suggestions..any further ones please feel free to post,

Thanks,

Team 1380

Re: Major mechanical problems....
 

if you're blowing the fuses on the CIMs by stopping it with your hand, then it's not geared down enough, end of story. That isn't a problem with friction in your drivetrain. You have 2 options:

1. Change your drive train to gear the CIMs down more. You could accomplish this by putting the 10 tooth sprockets on the output of the gears, and the 45 tooth sprocket on the wheels, and then run the chain between them.

2. Go back to your drills and try to figure out what's wrong with them.

Re: Major mechanical problems....
 

If that happens, you are most likely geared to high for your tire size and the CIMS. We are using chain to reduce the drill output to approx. 184 rpm for 12 inch tires. Reduction of 2.3:1. And that is like 10 ft/s. Still fairly fast. The rookie workshop reccomends to be in the range of 8 ft/s. Your best option would be to figure out if your reduction is right. The CIMS output 5500 no load and the drills output in the range of 20000 rpm with no transmissions. You would have to look at the specs for the transmission but low gear, all the way forward, is around 425 rpm and high is 1000+?? something. This is wear I would re-check figures so you will have enough torque. There are several good sheets on drivetrains in the white papers, but since you are running short on time I would get in contact with veteran teams around ATL to get some immediate help. It you find you are in a reasonable range there are other problem such as binding or problem with current (I doubt it would be this unless you are just running a low battery). Good luck and continue to ask questions.

Re: Major mechanical problems....
 

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

Re: Major mechanical problems....
 

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

Re: Major mechanical problems....
 

We had a similar problem with our drill drive motors last year. The root cause turned out to be current draw. We discovered this when we borrowed a portable ammeter from our electrical lab at work. The solution was to simply lower our gear ratio. The down side was that we could no longer use the drills in high gear for a high speed.

Re: Major mechanical problems....
 

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.

Re: Major mechanical problems....
 

are you guys running 2 cim's? and if you are are you running both motors through one fuse?, because that will definately cause them to blow under any load, the only other thing you could do is to de-sensitize the joystick signal with programming, but don't ask me how to do this, i don't do the programming for our bot.

Weighing the bot
 

Hey all. Hope all is going well and your successes are many this week. I've got a question about wieghing the bot. We measured earlier and were close, and are weighing all parts as they go on, but we'd still like to weigh the whole thing at once. Who does this? What's your techinique and/or piece of technology that you use?

Re: Major mechanical problems....
 

The official weigh in is during the practice day of the competition, by the volunteer robot inspecters.

We do our preliminary weigh-ins with a calibrated scale that was surplused from our corporate sponser.

The scale is an extremely accurate one formerly used in our space division.

Re: Major mechanical problems....
 

a good way to weigh your robot if you don't have access to a shipping scale is to take a bathroom scale and put 2 pieces of 2x4 on it then sit your robot on the 2x4 look at the weight and then subtract the amount of the 2x4.


also please let us know how the transmission problem went and if you need any immediate advise feel free to call me 410-963-6085

Re: Weighing the bot
 

When I was on 992, we threw the robot in the back of a minivan and drove to the nearest FedEx office. They were more than happy to let us use their scale.

Re: Major mechanical problems....
 

If the gearbox is assembled correctly, as was suggested in previous posts, then start of by removing the motors and turning the wheels by hand to see if there is any binding through the gearbox. Tweak the gearbox until all binding goes away. If those are 12 inch wheels, they ought to be spinning only 2 or 3 revs per second. 3 revs per second is about 9 feet per second, just to give you a ballpark estimate of speed. If those wheels are turning faster than that, your gear ratio is too high.

Good luck. We've all been there at one time or another. Just don't panic and start blaming anyone. Just concentrate on diagnosing the problem one piece at a time.