late van door question

[JKsenior05]

alright here goes Iam on a rookie team and we have been using a Taigene van door motor to power our arm. Our problem is that the motor starts off working fine with more than enough power, speed, and torque --- but after a short amount of time it slows down, loses power, torque, and becomes quite warm before eventualy shutting down. We believe this is the thermal protection kicking in, right? If it is Is there a way to possibly cool the motor by way of cutting vent holes in the exterior casing and placing a fan to blow freash air in? Or is the motor casing filled with oil or unable to be removed? please help

[Cory]

You cannot drill, cut, or otherwise modify the casing of the motor. Not only is it against the rules, it is a safety hazard and a good way to destroy the motor.

As to your problem, I have never experienced or heard of such a thing happening. Can you describe how you're using it in your arm to us in more detail?

[cdawzrd]

We are having similar problems with the VDM. When it gets too stressed, it just shuts down. Unfortunately, there is no easy way to deal with that.

[JKsenior05]

ok well first thanks for the feed back

second in response to the first reply

"You cannot drill, cut, or otherwise modify the casing of the motor. Not only is it against the rules, it is a safety hazard and a good way to destroy the motor." - Cory

5.3.4.1 Kit of Parts Rules
<R31> So that every robot’s maximum power level is the same, the motors in the kit may not be modified except
as follows:
•It is acceptable to modify the mounting brackets and/or other structural parts of the motors (output
shaft, housing, etc.) as long as the electrical system is not modified and the integral mechanical
system of the moving parts (bearings, bushings, worm gear output stages, etc.) is not changed or
removed.


I maybe wrong iam not sure on how its defined but those words allow for the possibilty possibilty of making ventalation holes in the housing/casing of the van door motor to vent hot air and yes you are right about it possibly posing a safety hazard so i was just wondering if it was a practical solution and if the housing/casing cant be removed or is filled with oil its out of the question but i dont know about those facts and the team doesnt want to risk damageing the motor without confidence that it will/should work

third reply number two

cdawzrd

We are using the motor to drive a bike chain and pair of gears. We built a fixed posting tower in the front and then attached the pivot point of the arm to the top.
The smaller of the two gears was placed at the bottem and the large at the top. I believe the math with accounting for arm length and tetra weight it came out to be gearing to something like a 1 to 3 or 1 to 4 ratio. Anway we have enough speed and torque to raise a tetra and hold it in place fairly quickly. But as metioned before the motor becomes rather warm and then slows down before stopping for several seconds. Thermal protection we believe. We came up with several ideas to fix it, adding a small counterweight ( but we have move part of the frame to make it work), adding a second motor to give it a boost ( however very time consuming), and of course finding a way to cool the motor so that the thermal protection dosnt kick in so soon. Then let the motor finish cooling off in between matches. Any thoughts? much apprecaited

[Katie Reynolds]

JK - please see this thread. The same argument ("We're modifying the housing") was brought up in this post.

Then FIRST updated <R31> in Team Update 5 to read:

<R31> So that every robot’s maximum power level is the same, the motors in the kit may not be modified except as follows:
• It is acceptable to modify the mounting brackets and/or other structural parts of the motors (output shaft, housing, etc.) as long as the electrical system is not modified and the integral mechanical system of the moving parts (bearings, bushings, worm gear output stages, etc.) is not changed or removed.
• The gearboxes for the Fisher-Price, and Globe motors are not considered
“integral” and may be separated from the motors. FIRST will not provide
replacements for parts that fail due to modification.

The intent is to allow teams to modify mounting tabs and the like, not to gain a weight reduction by potentially compromising the structural integrity of any motor.

By drilling into the housing, you are compromising the structural integrity of the motor.

[russell]

I personally would think it would be legal, though I wouldnt want to be the one arguing it out with the judges... More to the point I would be very hesitant to drill the housing as there are fixed magnets on the inside of it, and they are quite essential to the operation of the motor. I would want to get it x-rayed or something before trying to drill it. Again that is quite asside from the legality issues.

One thing you might want to do is talk to your programmer. Make sure he/she/it doesnt have it programmed to use some sort of sensor (potentiometer, gyro, etc) to keep the arm in position. I know I considered such an approach (If the joystick is centered then read the position of the pot and try to keep it in that position), but realised that it would have a tendency to burn out the motor and I abandoned the plot. Anyway, hope you get it worked out. I know the feeling of being crunched for time. We still dont even have a design for a tetra grabber.

[Rick TYler]

Originally Posted by JKsenior05

We are using the motor to drive a bike chain and pair of gears. We built a fixed posting tower in the front and then attached the pivot point of the arm to the top.
The smaller of the two gears was placed at the bottem and the large at the top. I believe the math with accounting for arm length and tetra weight it came out to be gearing to something like a 1 to 3 or 1 to 4 ratio. Anway we have enough speed and torque to raise a tetra and hold it in place fairly quickly.

We used the same motor with a fairly short arm (around 42 inches, IIRC) driven by sprockets and a chain with a 9:1 reduction. We've never had a problem at all. We calculated that 5:1 would be the minimum reduction we could use with our arm, but chose to go with 9:1 when we decided that speed of arm movement would not be a critical factor in the game.

Depending on your arm length, you may just be over-stressing the motor. Is it too late (Tuesday) to get a bigger sprocket for the top?

Good luck!

[JKsenior05]

thank you all for your input yes we are in crunch time and being part of a rookie team this is why I asked for help and clarification You guys have certainly done both for me and it is very, very much apprecaited well Iam off to meet up with the rest of the team for a couple more hours of work before we box up and ship out later today good luck to the rest of ya again thanks

[Kris Verdeyen]

Surgical tubing can often be used instead of a counterweight, with far less structural modification and added weight. Give it a look. If it's too late now (which it probably is) just ask around at the competiton - surely someone has tubing that they would lend you.

[Al Skierkiewicz]

JK,
There is a temperature sensitive cutout as I remember. (It is designed to prevent motor failure when a window is frozen.) You may not modify the motor case and doing so would only mask the real problem. You will find if you look at the problem that different motor power is needed throughout the rotation of the arm. At some points the power needed is small and at others it is quite large. Surgical tubing or other counter weight is an excellent way to quickly fix the problem. Just be sure to beef up the rotating joint to take the extra forces of the counterweight and arm.