Problems turning

[Gdeaver]

This years KOP wheels are flat. We drive on a 3d surface. The edges of the wheels tend to dig into the carpet. The skyway wheels Are slightly v shaped and not as grippy. The tend to turn better. Unfortunately, having the power of 2 cims to a side and tank drive makes things much better. We are using skyway wheels this year. They are cheap and adapters are easy to make. We also bought IFI AL sprockets for weight.

[Daniel_LaFleur]

Originally Posted by Dominicano0519

uhh we had a bad experience with zip ties in the Philly regional

In New Jersey they said it was perfectly legal; while in philly we ended up shaving all of the treads from our tires and waxing them every match becuase they said nothing mechanical could be added to the tires.

Sorry to hear that you weren't allowed to use them.

Last year I saw a good number of teams here in New Hampshire using Zipties.

As long as they can't damage the carpet, I don't understand why they can't be used. Can anyone post a rule as to why zipties cannot be used on the tires?

[Springman]

If you are using the stock banebots gear boxes, the first thing that I would do is replace the existing planetary gear set in the stock unit to the 4:1 gear in the change kit (available from banebots.) This will give you a 16:1 ratio vs. the stock 12:1 ratio. This will not negatively impact your weight issue, and depending on how accessible your gear boxes are, this swap can be made in 10-15 minutes easily. In addition, if you have reduction between your gearbox shaft and the sprocket at the tires, you can change the sprocket sizes to further increase your reduction. You will be giving up some speed everytime you make a change. If you do decide to buy omni wheels, you may want to buy extras. Several teams have had issues breaking the omnis in a 4WD configuration. The kitty-corner wheel configuration may help the breakage issue. The simplest test to perform on a drivetrain is to, on carpet, push against a wall. You should be able to spin the tires without tripping the breakers. Some simple things to check are:

1. Are you using the right fuses (40Amp.)
2. If so, are the fuses tripping when you are turning? If so, you will have to make a mechanical change.

[Joe Ross]

You should definitely read Chris Hibner's white paper called "Drive Train Basics" which describes the math involved with creating a drive train that turns. http://www.chiefdelphi.com/media/papers/1443

[Brandon Holley]

As with most things involving robots, there are tradeoffs. The omnis give you turning definitely, but they also give way in either the front or back. Try this:

If you take 2 omni's and put them on opposite ends meaning 1 on the front right and one in the rear left side of your robot, it reduces the lateral friction by 2 that you experience when turning. It also keeps a traction wheel in both the x and y axis. Im sure teams have done this before, but this is a fairly effective way of using omnis and keeping some of that traction.

[Alex Cormier]

well as stated many times before, omni wheels. But i am going with a new idea for you guys to ponder on. I see that you have the kit chassis, so if you have a little extra chain and weight if possible for some more sprockets, i say add a wheel in the center of the ones and make it a 6wd chassis. The kit chassis is designed to have the middle wheel lowered for ease of turning. It will really help with your turning solution.

[Justin M.]

We are running a similar drive setup this year as well, 4WD with 4 12:1 BaneBots gearboxes, with 15/24 reduction giving us 19.2:1 at the wheels. We are running 6"x1" IFI tractions in the rear, and AM omni-wheels in the front. Our wheelbase, however, is much shorter than your's as far as I can tell in the picture.

[Al Skierkiewicz]

Originally Posted by Dominicano0519

uhh we had a bad experience with zip ties in the Philly regional

In New Jersey they said it was perfectly legal; while in philly we ended up shaving all of the treads from our tires and waxing them every match becuase they said nothing mechanical could be added to the tires.

Dom,
This has come up before but I do not understand the inspector's decision without talking with them. As long as the mods meet the rules they should have been allowed. I have recommended this fix for teams who were having a problem and couldn't find a fix quickly. Tywraps obviously are allowed since they are supplied in the KOP. More accurately the rule is...


<R34> ROBOT wheels, tracks, and other parts intended to provide traction on the playing field may be purchased or fabricated (“traction devices” include all parts of the ROBOT that are designed to transmit any propulsive and/or braking forces between the ROBOT and the playing field). In no case will traction devices that damage the carpet or other playing surfaces be permitted. Traction devices can not have surface features such as metal, sandpaper, hard plastic studs, cleats, or other attachments. Anchors (i.e. devices that are deployed/used to keep one’s ROBOT in one place and prevent if from being moved by another ROBOT) can not use metal in contact with the carpet or other playing surfaces to “stay put.” Gaining traction by using adhesives or Velcro-like fastener material is not allowed.

As long as the lock part of the tie is positioned to the inside of the wheel, there will be no "hard plastic stud" in contact with the surface. A little hot glue to hold it in place doesn't hurt either. There is other possibilities as outlined above but this does provide a quick fix.

[DonRotolo]

Originally Posted by Alex Cormier

i say add a wheel in the center of the ones and make it a 6wd chassis. The kit chassis is designed to have the middle wheel lowered for ease of turning. It will really help with your turning solution.

Note that the center wheel does not need tot be powered for this to work.

It will definitely not help with your weight issue. 5 pounds is far too much to be had by putting holes in aluminum.

What is the material used for the ramp surface? It looks like aluminum with holes - if so consider a much lighter material, like 1/8" aviation plywood (sold at hobby shops). Far lighter, brutally strong. Or somehting like that.

1/2 pound per ramp can be lost by holing the ramp frame

We lost 1/4 pound in wire this year by just cutting things to length.

good luck with that

Don

[TheFuhr]

Ahhhh the four wheel pneumatic drivetrain...
Such a horrible idea...
We used that last year and never will again.
Broke so many chains jerking around the field.
We installed castors but they only make the jerking smoother.
My advice, use two omni-wheels, its the only way to save yourself.

[meatmanek]

Originally Posted by Cody Carey

Since surface area has no bearing on friction, I would assume that this would be a bad Idea. By putting the two "sticky" wheels beside each other, you are reducing the amount that the wheel has to be pulled sideways when turning, and increasing the amount that it rolls along the turn. This decreases over all turning friction.

If you were to place them on opposite corners, it would do nothing to the amount that the sticky wheels have to be pulled sideways to follow the circle of your turning radius, and since One wheel has the same amount of friction as two, I wouldn't expect this to solve your problem at all.

Not true. One wheel with 60 pounds on it has the same amount of friction as 2 wheels with 30 pounds each. However, one can assume that the weight of the robot will be approximately equally distributed across the four wheels, or at least the weight on the omnis will be the same as the weight on the traction wheels. Therefore, the traction wheels have only half as much turning friction as they used to.

Another solution would be to move your wheels closer to the middle of your robot. This increases turning capacity without decreasing traction. However, it causes balance problems, as your wheel base is shorter. Add a few trick wheels or casters that hover just above the ground to fix this problem.

[Cody Carey]

Can someone please explain this to me mathematically? I still don't get it.

It takes less force to rotate a wheel along the diameter of the turning circle than to scrub it sideways along the same circle. With the omni wheels in the front (right picture),you are basically applying force tangentially to the circle which you turn on, and with the omni wheels on opposing corners, You are waisting a lot of your force going outward from the turning circle, and scrubbing both traction wheels sideways.

Is it just that having the omnis on opposite corners woud decrease the force required to turn the robot, but not as much as the omnis on front of back would do? A little help would be greatly appreciated.

[Tom Bottiglieri]

Originally Posted by Cody Carey

Is it just that having the omnis on opposite corners woud decrease the force required to turn the robot, but not as much as the omnis on front of back would do? A little help would be greatly appreciated.

Yes.

While the second scenario you illustrated will get you closer to a "zero friction" turn, it also changes your turning radius from dead center in the robot to inside of the axis between your back two wheels.

Putting the omni's in opposite corners still gives you the problem of turning scrub, but it will significantly reduce the problem as half of your total weight is being distrbuted along wheels which experience little to no axial frictional force. For most situations, this should be enough to kill the bouncing robot problem. This also allows you to keep your 0 degree turn radius, and keep a solid wheel on the ground on each side of the bot at all times.

So really, its all up to driver experience and preference. I have been told that drivers who like to use one stick drive will be much better on a "power slide" bot (omnis on same side) and drivers who prefer two stick will be much better with a 0 degree turn radius.

[Bochek]

well today we ordered 3 andy mark 6" omni wheels,

the reson for 3 was incase one breaks.

we will be replacing the 2 rear wheels with the onmi wheels.

does anyone know the difference in weight between the ifi aluminum sprokets and the steel KOP wheels?

- Bochek

[Arefin Bari]

Originally Posted by Bochek

well today we ordered 3 andy mark 6" omni wheels,

the reson for 3 was incase one breaks.

we will be replacing the 2 rear wheels with the onmi wheels.

does anyone know the difference in weight between the ifi aluminum sprokets and the steel KOP wheels?

- Bochek

The KOP wheels weighs .8 lbs. I believe you were trying to ask about the sprocket that was provided in the kit. If you are wondering if it would help you lose weight when you switch those steel sprockets to aluminum ones, yes you are on the right track.

Also, you are already going to lose .6 lbs by planning on swtiching those kop wheels to AM omni wheels. Those AM omni wheels weigh 5 pounds.

If you need help figuring out how to lose more weight and if you have detailed/close up pictures of the robot, feel free to contact me. I will be more than happy to help you guys and give some suggestions.