Re: BIG Tires
 

Big tires you say?
DIY
Smaller of the same idea but no rubber

Seriously what is stopping someone from making a wooden, or combination aluminum/3D printed rim, for any size tire they like?

Same basic ideas could be applied to this:
12" spoked tire from Northern

Re: BIG Tires
 

Good question. The way I showed the ratio, bigger is better.

WideBots can turn. NarrowBots have troubles.

The reason lowering the center wheel works so well on a 6WD robot is that it allows NarrowBots to pretend that they are WideBots (in a sense) because only the 4 front wheels or the 4 back wheels can be in contact with the ground at once SO the ratio is approximately doubled (the top stays the same, the bottom is halved).

Careful readers will notice something and be worried (possibly). In order for this to work you have to actually get a set of wheels off the ground (or at least unloaded). With pneumatic wheels and uneven floors the assumption that lowering the center axles 1/8" is going to be enough may not be such a great assumption. It also means you are going to have to pay attention to the pressure in your tires -- you can easily make a great turning robot into a dog by allowing the pressure in the center tires to go down a bit.

Think about it.

YMMV.

Dr. Joe J.

Re: BIG Tires
 

Another way to reduce the turning radius of an otherwise 4 wheel robot could be the old Batmobile stunt:

Lift the robot up on smaller pivot underneath breaking the traction between your large outer 4 tires and the ground then turn on that pivot. Course you probably have to stop to do that.

Re: BIG Tires
 

Not true. I think many teams have done something like this where they dropped a pneumatic turn assist foot whenever they needed help turning.

I will let other who know better give examples but i am 99% that a number of robots designed by Raul the Magnificent formerly of Wildstang (#111) now (like so many great FIRST engineers) working at Bob & Tony's Excellent Adventure in TX.

Let those with knowledge share it.

Hold Strong,
Dr. Joe J.

Re: BIG Tires
 

If you use a six drive pneumatic drivetrain, what kind of programming do you use for the driving, tank?

Re: BIG Tires
 

This is a discussion for another thread perhaps but the short answer is "whatever your drivers like best." Either can be successful. Drive preference is the most important factor to consider (imho).

Dr. Joe J.

Re: BIG Tires
 

Well you first problem is that it's a wheelbarrow wheel. The hub on that is designed to spin freely. So your going to have to make and design all new hubs for every wheel and these new hubs are going to have to be able to take all the torque your putting on them.

Re: BIG Tires
 

I was thinking about how to drive the "wheelbarrow" wheels, which have a tube with bearings in the ends. My idea is to make a steel hub, with an ID the same as the OD of the tube, and a 6 hole bolt pattern to match common robot sprockets. Tack weld the hub to the tube.

But I haven't actually done this yet! and I have some equipment that other teams may not have access to, although I think you could do it with nothing more than a hole saw and a drill press and hack saw, if you needed to. Oh, and a MIG welder, although there are plenty of shops that could weld something like that pretty easily.

Re: BIG Tires
 

Depending on the forces involved:

In the past I bought some tires from Tractor Supply made a jig to drill out a bolt pattern that I also put into some G&G Manufacturing cast sprockets. I put a piece of PVC around the bolt pattern as a big spacer. A good shot might break that alone but I packed it with Shapelock. In place of PVC one might use EMT as well.

It simply worked and I've seen a few go-karts setup like that as well.
Just keep in mind you need to be careful matching your part selections to make this as easy as possible.
BTW it's heavy so if weight is your concern think it over some more.

Re: BIG Tires
 

If you're firing up a welder, why not just use the COTS built-in bearings on dead axles and weld the sprockets to the wheel, possibly with a short length of tubing to move the sprocket away from the bearing? (You will need steel sprockets, but no hub, so it shouldn't weigh any more.)

Re: BIG Tires
 

The manufacturer claims that they are not for highway use.

Re: BIG Tires
 

oh well, better not use them on carpet with a robot just to be safe. I have been racing in the Power Racing Series. There are competitors there using all sorts of completely out of spec tires and wheels because of a $500 maximum budget. Pretty much any pneumatic tire should be fine for FRC. Even the cheap HF tires should last an entire weekend of FRC use.

You do the power racing series? As in the one they show off at Makerfaire every year?