HELP!

[Vikesrock]

Originally Posted by bobdahaxor

the first picture has our drive train. Also, if we move the battery and compressor closer to the front wheels would that help? I think we are gonna try the 16:1 boxes for now and maybe smaller wheels if we can. Appreciate all the help and if anyone has any other suggestions, that'd be great!

While moving the compressor and battery towards your driven wheels may help, it may also create huge Center of Gravity problems when holding a trackball up in the air. You may be very, very tipsy if you move those two items to the front.

The other two things you mentioned should both help turning with the only real tradeoff being speed.

[DonRotolo]

Moving some weight towards the driven wheels will help. The force needed to turn the bot is increased when the weight is close to the omni wheels. Try this to see what I mean: Swing a sledgehammer in a circle, first with the head away from you and then with the head in your hands. Do you need more force to swing it when the head is in your hands, or less? That force comes from your wheels, and a single CIM is reaching the upper limits of the torque it can provide.

[ll4m4ra0r]

Is it possible that the reason it was not turning is that the transmissions were dry on the inside? The drive worked fine at playdate, on carpet, and since then, the drive has not turned well. We opened the used transmissions up on thursday of competition and they were dry on the inside (not well greased), when they were librally greased on the inside when they were new. It could have been binding, and that could be our problem. Who knows what Fed-Ex does to those crates to dry that lube up....

[Vikesrock]

Originally Posted by ll4m4ra0r

Is it possible that the reason it was not turning is that the transmissions were dry on the inside? The drive worked fine at playdate, on carpet, and since then, the drive has not turned well. We opened the used transmissions up on thursday of competition and they were dry on the inside (not well greased), when they were librally greased on the inside when they were new. It could have been binding, and that could be our problem. Who knows what Fed-Ex does to those crates to dry that lube up....

This could definitely be your issue. Transmission binding due to too little grease will sap the efficiency of the transmission. This will lower your available output torque, potentially enough to make turning difficult.

[Al Skierkiewicz]

I believe your tranmission reduction choice is not low enough. Looking at your 8" wheels being fed directly by the output of the 12:1 tranny makes me think impossible. Could someone check my math while I go do an errand, I backed into a calculation that this design is too low a torque to actually pull much weight. I am guessing that the motors are running very hot after a match and are likely tripping the breakers.

[JHSmentor]

I have some clarification questions and then an answer based on my assumptions (questions).

1. Can you turn the robot well when you are already moving?
2. Does the problem only happen when you are sitting still and you want to turn without moving forward first?
3. do you have the wheels on one side go in reverse when turning or are you trying to turn with just one drive wheel? (see our experience below for why I ask this question).

While I think that everyone's suggestions with weight distribution and everything is valid, it may be somewhat difficult to change now that your robot is basically built. But, it may be your only choice for now.

Our robot is a six wheel drive with omni's in the front and back and KOP wheels in the middle. One problem we had initially with turning (or stearing that matter) is that the wheels on the side the robot was turning to would get thrown into reverse - even when the robot was moving forward. this caused the it to turn very quickly (and make some aweful noises). Sitting still, however, it could easily spin on a dime (6 wheel does that for you). Our fix was to program the joystick to only throw the wheels in reverse on one side when the joystick was nearly pushed all the way to the side. This allowed both sides to drive forward while steering as well as to allow us to spin while sitting still.

So, if you are not already doing something similar, you may consider a program change to reverse one motor while going forward with the other but only allow this when the robot is sitting still or when the joystick is pushed all the way sideways. Control the speed of the spin or turn with programming.

Anyway - hope this is useful. otherwise, good luck.

[bobdahaxor]

I have some clarification questions and then an answer based on my assumptions (questions).

1. Can you turn the robot well when you are already moving?

Better, but not amazingly

2. Does the problem only happen when you are sitting still and you want to turn without moving forward first?

more or less yes

3. do you have the wheels on one side go in reverse when turning or are you trying to turn with just one drive wheel? (see our experience below for why I ask this question).

one is in reverse and one is going forwards

[ll4m4ra0r]

To all you non-believers :

We drove around for a few solid 30-minute intervals with the drive on linoleum. (After each time the drive was very hot though. ) Granted, it's not carpet, but hey, when it was working, it didn't have overheating problems after a match. We went to, and performed very well at, a "playdate" the Saturday before ship date on the NASA-Goddard field, and the drive worked beautifully (until we had an issue with bending an omni on a plate). So that leads me to believe very strongly that there is not a fundamental design problem so much as a newly-acquired mechanical problem.

[EricH]

Originally Posted by ll4m4ra0r

To all you non-believers :

We drove around for a few solid 30-minute intervals with the drive on linoleum. (After each time the drive was very hot though. ) Granted, it's not carpet, but hey, when it was working, it didn't have overheating problems after a match. We went to, and performed very well at, a "playdate" the Saturday before ship date on the NASA-Goddard field, and the drive worked beautifully (until we had an issue with bending an omni on a plate). So that leads me to believe very strongly that there is not a fundamental design problem so much as a newly-acquired mechanical problem.

Problem #1: non-carpeted surface in testing, and your motors are very hot. There's something there that just doesn't sound right, even though you carpet tested on the Goddard field. I think it is a design problem.

[ll4m4ra0r]

The issue we have is, why did it work on the NASA field, but not at the regional? The only thing i saw different was the dry transmissions, so that's my only guess.

[TubaMorg]

Another thing to look at (in addition to every thing else already said):

We used the banebots transmissions last year (12:1 direct drive). We had a different drive setup with 4 driven mec wheels. However, one of the wheels would catch intermittently. We couldn't replicate the problem in the pits, but eventually discovered that the sticky wheel was ever so slightly out of alignment, causing the planetary gears to stick.

I'm not sure if this is applicable to your banebots transmissions since they have made some design improvements from last year, but they are sensitive to side loading. It could be that during turns you are adding enough twist to the frame that it is causing binding in the transmissions due to an introduced side load on the drive shaft.

[T3_1565]

Originally Posted by TubaMorg

I'm not sure if this is applicable to your banebots transmissions since they have made some design improvements from last year, but they are sensitive to side loading.

I disagree. Our drive system found here puts more side load on the transmissions then most drive systems will. and with three weeks of driving (on carpet) we still have no problems what-so-ever (knock on wood )

It seems to me the transmissions being dry may be the biggest problem.

Secondly, can you turn the traction wheels by hand? (you should be able to, we can) If you can't maybe its the way you mounted the wheels?? I haven't seen wheels mounted that way before(not saying its bad, its just different for me) and may cause a "brake pad" effect... although you said no problems with driving striaght... how well can you drive backwards?? if you are turning like normal skid steering, then maybe thats what is cause the problem.

Hope it gets fixed and good luck!

[ll4m4ra0r]

Originally Posted by T3_1565

I disagree. Our drive system found here puts more side load on the transmissions then most drive systems will. and with three weeks of driving (on carpet) we still have no problems what-so-ever (knock on wood )

It seems to me the transmissions being dry may be the biggest problem.

Secondly, can you turn the traction wheels by hand? (you should be able to, we can) If you can't maybe its the way you mounted the wheels?? I haven't seen wheels mounted that way before(not saying its bad, its just different for me) and may cause a "brake pad" effect... although you said no problems with driving striaght... how well can you drive backwards?? if you are turning like normal skid steering, then maybe thats what is cause the problem.

Hope it gets fixed and good luck!

It should be noted that the omnis also spin freely, and all the rollers spin freely as well.

The wheels can be turned fairly easily, but we avoid forcing the wheels to prevent damage to the electronics On second thought, we never tried spinning the ungreased transmissions. Thanks, as soon as we get our hands on our robot were gonna try some greased up transmissions.

[T3_1565]

Originally Posted by ll4m4ra0r

It should be noted that the omnis also spin freely, and all the rollers spin freely as well.

The wheels can be turned fairly easily, but we avoid forcing the wheels to prevent damage to the electronics On second thought, we never tried spinning the ungreased transmissions. Thanks, as soon as we get our hands on our robot were gonna try some greased up transmissions.

unplug from electronics

[ll4m4ra0r]

Originally Posted by TubaMorg

Another thing to look at (in addition to every thing else already said):

We used the banebots transmissions last year (12:1 direct drive). We had a different drive setup with 4 driven mec wheels. However, one of the wheels would catch intermittently. We couldn't replicate the problem in the pits, but eventually discovered that the sticky wheel was ever so slightly out of alignment, causing the planetary gears to stick.

I'm not sure if this is applicable to your banebots transmissions since they have made some design improvements from last year, but they are sensitive to side loading. It could be that during turns you are adding enough twist to the frame that it is causing binding in the transmissions due to an introduced side load on the drive shaft.

Do you mean the wheels would push the transmissions to the point of binding?