HELP!

[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 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?

[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

[TubaMorg]

Originally Posted by ll4m4ra0r

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

That is correct, but it only happened to one of our transmissions. It could be that the newer transmissions can accomodate the side load better, though, so make sure you try all the suggestions possible here. Hopefully you can solve it easily with some grease, rather than a complete redesign.

[ll4m4ra0r]

Originally Posted by TubaMorg

Hopefully you can solve it easily with some grease, rather than a complete redesign.

Crossed fingers. I've seen other teams use 2 cim drives with the same setup, and it worked fine, so it can't be design problems only.

[Ken Streeter]

Originally Posted by 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

Thanks for the clarifying questions; they help provide some clues as to what is actually going on.

One of the issues with a 2WD system is the issue that was pointed out by dtengineering in his post -- you want as much of the weight to be on the driven wheels (in your case, the IFI traction wheels) as possible, with as little weight as possible on the undriven wheels (the omni wheels).

When the robot fails to "spin in place" when you drive one wheel forwards and one in reverse, which of the following happens? (1) The traction wheels spin on the carpet, with one going forwards and one going backwards, or (2) the motors are stalled out, trying to rotate, but nothing is moving at all, the wheels aren't even spinning.

If the problem is case (1) with the spinning wheels, you should be able to resolve the problem by moving heavy components from the omni-wheel end of the robot to the traction-wheel end of the robot. In particular, the compressor and battery are two excellent candidates for this. I suspect that this scenario is the problem that you are experiencing. Any weight you can move from over the omniwheels to over the traction wheels helps in two ways: (a) by reducing the resistance to turning since there is less weight on the undriven wheels and (b) increasing the traction available to the drive wheels by increasing the weight on those wheels. If the wheels are spinning due to a lack of traction, no gear ratio changes will be able to fix the problem.

The other possibility is case (2) with the traction wheels being stalled out. I would be amazed if this is the problem, as there is actually quite a lot of torque available in your transmission setup. If this is happening, it is almost surely due to your omni wheels not sliding sideways readily, either because they are somehow getting caught on the carpet, or the rollers are not spinning easily. Another possible root cause if you are seeing this problem would be binding of the transmission mechanism.

As for the single CIM drive mechanism potentially having insufficient power, our team's hurdling base used a single CIM drive on each side, with a final ratio of about 19:1, but using 12.5" wheels, giving almost exactly the same peak travel speed (and thus the same torque, since we are using the same motors) as your configuration. We had no troubles turning, but we had the weight of the robot very nearly centered over the drive wheels. This configuration still had excellent acceleration, even though it wouldn't win many pushing matches.

I believe that moving weight from the rear (the omni end) of the robot to the front (the traction wheel end) will probably solve your turning problem. However, it will also introduce another problem that your drivers will need to deal with... When the weight is largely over the front driven wheels and you then are traveling forward at full speed and suddenly apply full reverse power, the robot will have a big tendency to tip over forwards. Just something to watch out for...

Please let us all know what you end up doing to fix the problem.

[ll4m4ra0r]

Thanks for all your input everyone! We initially replaced the omnis with Andy Mark Coolie Dualie wheels, and shifted the battery forwards. We still had issues with overheating and not being able to turn, and resorted to replacing the 12:1 transmissions with 16:1 transmissions. This solved our issues, and surprisingly, there was almost no noticeable speed decrease. The cims would be at around 10 degrees above ambient temperature after every match, and we could turn fine. In the end, there was just not enough torque with the 12:1 transmissions, and it just couldn't turn.

After we fixed the drive, we went on to be quite effective at Philadelphia, and we are looking forward to Atlanta!