Carpet at Competition

[Hebrew]

Hi,

I am part of a rookie team. We didn't get as far as I wold have liked this year but we managed to get a working robot, it can't shoot very well so we will just be doing defense. We recently took our robot to our schools library to test it out on carpet but it could not turn at all. The robot locks up and will not move for a small amount of time. The carpet that we used it on is a short, harder style carpet. We tried putting masking tape on the wheels. The masking tape ripped off very fast. We put duct tape on the wheels and it just spun out which would not work playing defense. We put some sand paper on the wheels and it could not turn.

Our robot is just right in the dimension limits and is operating with the wheel from the KOP. It is a tank drive with a motor on each side toward the back of the robot.

What I the carpet like at the competition?

Is there anything we can do to fix the wheel problem fairly fast? We are going to a scrimmage tomorrow.



Thanks.

[CalTran]

If we could have some information about your drivetrain we could also help. As well, I don't believe adding tape is the way to go to increase traction.
To answer your question about the competition carpet, as per Section 2, The Arena,

The Court is covered with carpet (Shaw Floors, Philadelphia Commercial, Neyland II, 20, 30753, “park bench”).

This is the carpet to be used at competition.

[EricH]

The competition field is going to be pretty much what you tested on.

As for traction, try this classic trick:

1) Get lots of zip ties.
2) Place the zip ties on the rims of the wheels on one end of the robot.
3) Replace any zip ties that come off.

You could also:
--Add a dropped center wheel (if you're using the KOP frame, the center hole on the side rails is dropped down slightly already).
--Change one end for omni wheels (more expensive, and you'd have to wait for them to arrive).
--Add a CIM to each side and make sure all your wheels are powered.

[Cory]

Add a motor to each gearbox.

Are you using 6 wheel drive?

[midway78224]

What drivetrain setup are you running. We ran into the same problem and had to switch to a gearbox with a higher gear ratio.

[Hebrew]

We probably do not want more traction if the wheels lock up, do we?

We are using four wheel drive and the frame is the standard from the KOP. Will six wheels really increase the chances of turning?

All of our wheels are getting powered from the two motors.

[EricH]

Originally Posted by Hebrew

We probably do not want more traction if the wheels lock up, do we?

We are using four wheel drive and the frame is the standard from the KOP. Will six wheels really increase the chances of turning?

All of our wheels are getting powered from the two motors.

Yes, plant two powered wheels in the center holes of the KOP frame. Those two holes are lowered, which is why this will work. (You shorten your wheelbase a little bit, which really does help.)

[CalTran]

If you can switch to 6 wheel center drop, then yes, it will turn easier. The idea behind center drop drive trains is that it shortens the distance between the wheels on the ground and so they can turn easier. In standard 6 wheel drop, there will always be 4 wheels on the ground and it will "rock" when it turns and/or drives.
As well, if you can change it to 4 CIMs, it will be much easier to play defense.
My personal opinion would be at least ensure your ball manipulator can shoot balls enough that you could feed to your alliance partners from the opponents zone, keeping in check the various penalty rules

[Hebrew]

So all we do is hook up the two wheel like the pervious four, add a sprocket and we are good to go? Or is there something fancy to do? (No one is currently at the robot so I cannot check myself and we will be doing this immediately tomorrow morning).

Is there extra sprockets in the KOP?

Edit: I am not on the build team so some of my questions might be silly, but they didn't do it so I am switch I am helping out since I have nothing else to do

[EricH]

Originally Posted by Hebrew

So all we do is hook up the two wheel like the pervious four, add a sprocket and we are good to go? Or is there something fancy to do? (No one is currently at the robot so I cannot check myself and we will be doing this immediately tomorrow morning).

Is there extra sprockets in the KOP?

Nope, nothing fancy. The bad news is that only 4 sprockets came in the KOP; for a short-term solution, move the wheels on the light end of the robot to the middle and have the wheels at that end unpowered until you can get sprockets in. (The KOP sprockets can be found at http://www.andymark.com/product-p/am-0737.htm for $9+shipping; I'd get 4 so you can have a shorter chain run to the front wheel.)

[Hebrew]

Ah, so we split our long chain into two medium chains for each side.

Is there absolutely no temporary solution for a four wheel drive so we can still do decent at the scrimmage we are going to tomorrow?

[EricH]

Originally Posted by Hebrew

Ah, so we split our long chain into two medium chains for each side.

Is there absolutely no temporary solution for a four wheel drive so we can still do decent at the scrimmage we are going to tomorrow?

Yep, move the powered wheel to the center and leave the light end unpowered.

Or, as I noted earlier, wrap zipties all around the rim of the light-end wheels. That's one of the oldest tricks in the book, and it works as a temporary measure. (Or a permanent one, in some cases.)

When I say "light end", often robots (particularly 6WD robots) will have one end heavier than the other, which means the CG is slightly to one end or the other. The wheels where the CG is not tend to carry less weight, so modifying them is less detrimental to traction.

[Hebrew]

Thanks for the help, we will try the zip tie thing tomorrow and then as a last resort unpowered six wheel drive.

[Bill_B]

Originally Posted by Hebrew

...
Is there anything we can do to fix the wheel problem fairly fast? We are going to a scrimmage tomorrow.
Thanks.

That's the good news. At the scrimmage there will be a lot of people who will be happy to help. They may even be able to supply the mentioned zip ties for you. Don't put the "fat" ends on the bottom!

BTW, the reason the zip ties work, is that they will act like little skis for sideways movement of the wheels and reduce the forward/backward traction an acceptable amount. The reason you're having difficulty steering is the traction between your wheel and the carpet is pretty much the same in all directions and turning tries to make the wheels to go side to side against that traction.

[Hebrew]

If you are interested:

At the scrimmage instead of using zip ties we used electrical tape on the wheels to assist in turning. We only did four matches because we were also testing drivers and two of them destroyed our pistons by running into the bridge which really slowed us down. We fund that the tape worked fairly well if used on two wheels but had to be replaced after each match because it loses it's slip. We will be testing zip ties out on Monday or Tuesday.