Re: Casters vs. Unpowered Omni wheels
 

If it was a line following bot you could get away with autonomous. But no guarantees.

Re: Casters vs. Unpowered Omni wheels
 

For what it's worth, back in college, I took an Autonomous Robotics class - essentially, we played with MIT's HandyBoard and a bunch of Lego's all semester, with a game/competition at the end of the semester. I ended up designing a caster wheel (out of the provided Lego's) to use on the robot (2 drive wheels in front, 1 centered caster wheel in back) The biggest problem we had with the wheel, before we got it designed right, was it pulling apart or pulling out of the joint where it attached to the robot - there was simply too much force on it when the wheel was trying to turn (and we designed for 90% of the weight to be over the drive wheels)!

Now, given the situation, the caster wheel provided us with a great advantage - Unlike all the other robots (which had 4 traditional drive wheels - no one tried doing a 6-wheel drop center... hadn't even heard of it at that point), ours didn't have to overcome scrub on the wheels when it was turning, and we could turn around the center point between our drive wheels. This simplified other aspects of the design, as the robot could rapidly spin in place to identify the polarized guide lights, while other teams had rotating sensors and then had to line the robot up with the sensor.

Based on that experience, I say casters do have their purpose... but it's going to be a very rare game/robot design where it provides a benefit to a FIRST robot, given all the other options we have (dop center, omnis, etc).

Re: Casters vs. Unpowered Omni wheels
 

We once built a 2wd occra robot with rear straight casters and front skids. It was very back heavy, so the skids rarely hit the ground.

We quickly replaced the rear wheels with lunacy wheels, driven.

Don't use casters. Use driven omni or lunacy wheels.

Re: Casters vs. Unpowered Omni wheels
 

Ha ha, I remember we had so much trouble with that, until we switched to treads, but then we had even more problems with that! But I would definitely rather use unpowered omnis if we had the budget, cuz they don't change directions as easily from bumps. Also, casters cannot deal with uneven terrain, which is a little easier on omnis. My favorite type is mech, because it actually tank drives when you need it, and is much simpler.

Re: Casters vs. Unpowered Omni wheels
 

Casters are a pain in the rear to work with (in my opinion). They swivel around, which can mess up autonomous for the robot. Also, if there are bumps in the field again (like 2010), casters are much more likely to break than a slick wheel from 2009 (which has the same effect as an unpowered omni). Overall, slick wheels are an easier and much more reliable solution.

Re: Casters vs. Unpowered Omni wheels
 

The 2009 slick wheels, though, have a much higher CoF in the sideways direction than an omni wheel (which is near zero, due to the sideways rollers). So, they will drag, which makes turning that much harder. While it won't be as bad as a 4WD all-traction setup (which could be really bouncy, depending on traction), it still won't quite perform as well as an omni wheel, powered or not.

Re: Casters vs. Unpowered Omni wheels
 

We used them in Rack and Roll. It remains to this day the most disastrous engineering decision we've ever made. (And we've made some doozies!)

Re: Casters vs. Unpowered Omni wheels
 

We used them in 1997 and I was a driver. They work fairly well if the rest of the machine was designed to work that way and the use a more sweeping style of driving than sudden direction changes. We even had mixed control with single joystick instead of dual joystick tank drive.
Our machine was a front wheel drive tail dragger. It had a forward heavy CG and would scoop tubes and reach forward.
The event was Toroid Terror and the event was in a hexagon with a center mounted goal.
The year prior we used a 2wd center mounted with solid pads instead of casters in the 4 corners. it was tank driven and was fine, just rocked a little.


However in this years event there is no way they would work with the ramps/tables.