Major mechanical problems....

[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.

[Kevin Sevcik]

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

[quickie25]

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

[Kevin Sevcik]

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.

[ngreen]

Originally Posted by quickie25

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

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.

[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

[Peter Matteson]

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.

[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.

[spyder_man]

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.

[Steve Compton]

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?

[Peter Matteson]

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.

[Greg Needel]

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

[ahecht]

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.

[Warren Boudreau]

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.