Problems turning

[Ben Piecuch]

Thanks for clarifying the drive train.

With that information, omniwheels are probably your best choice in this situation, due to weight and time contrainsts. If the weight of your robot is equally balanced between the front and the back (a 50/50 weight distribution) then it doesn't matter which side you put the omniwheels on. Basically, it would come down to the driver's preference as to which end of the robot gets rotated. I would suggest looking at some video of FRC176 this season. They are using omniwheels on the back of their robot, and you can see how it significantly changes the style of driving.

If the robot is significantly heavier on one side or the other, it is advantageous to put the omniwheels on the lighter side of the robot. With your traction wheels on the heavy side, you will transmit more power to the ground, and the robot will turn even easier.

Having the 4wd setup has already provided a huge step up in performance, as you probably realized during testing with the lighter kitbot setup. Mounting a chain and sprockets to some of the cheaper, generic omniwheels is a little more complicated than just a drop in solution. I feel that the Andy-Mark 6" omniwheel is your best solution, as those wheels are a direct replacement for the existing 6" wheels.

One other solution, which may not be widely accepted here, is to find an old 6" skyway wheelchair wheel. These are the old kitbot wheels which teams used in previous years. They are not as grippy as the new kit wheels, and could provide you the right balance between side slip and lateral grip. With the proper wheel hub, these are also a direct drop-in solution.

Best of luck.

BEN

[Daniel_LaFleur]

Originally Posted by Bochek

sorry, the drivetrain is the banebots 56mm gearbox with a CIM and 4wd.

basically the standard kitbot chassis but with added sprokets and chain to make it 4wd.

so replacing the rear wheels with omni's could prove a good solution then?
and i would still keep it 4wd correct?

- Bochek

This will work well (we've used it in the past).

A inexpensive alternative is putting zipties on the rear set of wheels. Putting about 10-20 zipties on each wheel (equally spaced) will reduce the traction of those wheels. The more zipties, the less traction. As with Omniwheels, as your traction goes down it becomes easier to push you around.

[Dominicano0519]

Originally Posted by Daniel_LaFleur

This will work well (we've used it in the past).

A inexpensive alternative is putting zipties on the rear set of wheels. Putting about 10-20 zipties on each wheel (equally spaced) will reduce the traction of those wheels. The more zipties, the less traction. As with Omniwheels, as your traction goes down it becomes easier to push you around.

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.

[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.

[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.

[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.

[Dominicano0519]

Originally Posted by Bochek

sorry, the drivetrain is the banebots 56mm gearbox with a CIM and 4wd.

basically the standard kitbot chassis but with added sprokets and chain to make it 4wd.

so replacing the rear wheels with omni's could prove a good solution then?
and i would still keep it 4wd correct?

- Bochek

where you turning at full speed?
Try telling your programers to make the wheels spin in opposite directions when turning.

also you might want to consider sliding the wheels closer together to get smoother turning it really helped us out since we had a 4wd robot last year that jumped around like a bull

this year just with replacing tires and moving the wheels closer it turns like an RC car

[silicon_ghoti]

From what I've seen on other forums it would seem that all omni-wheels causes you to be pushed, I would suggest doing what li'l Lavery said and if you have a 4 wheel base, put on 2 omni-wheels in opposite corners of the robot, this allows for easier turning and you're still hard to push. On the aluminum bearings I am no help (sorry I'm an EE guy.)

(The wheel design looks like this the parenthesis are omnis and the straits are regular wheels.)


()____________________||
()____________________||
()____________________|| <----these are regulars
()____________________||
()____________________||




||____________________()
||____________________()
||____________________() <---these are omnis
||____________________()
||____________________()

[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.

[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