Virginia is a land based robot that was designed for the 2008 FIRST Overdrive Competition. Virginia can be programmed to be full autonomous, full tele-operated, or a hybrid of the too. The Robot Controller is a Innovation First Controller that is pair with an operator interface. The frame is made of mainly extruded fiberglass; Virginia can pick up a ten pound forty inch diameter ball and launch it seven feet vertically and about thirty feet horizontally!
Tell us all about the omni wheels. What were the disadvantages, why did you combine them with regular wheel, was it hard to program the omni direction performance, etc?
The Competition gives you six weeks to have a working robot, there is on event called the Kick-Off, this is when worldwide the competition is announce (because the game changes every year). That means every team gets the message at the same time. Also at the kick off your are handed a KoP (Kit of Parts). The basic robot parts are in it, RC, Motor Speed Controllers, Spikes, all the things that make you robot run.
I will have to look for a video of the transmission then post on YouTube but for a quick reply here is a picture of the how the servo is mounted. It Runs on 7.2 volts and it power right from the RC. They worked great, but one servo did burn out. This was do to bad programming. We had it at full 255 when really it should have be 220. It was continually getting resistance in first gear.
As for the transmission, it is bulletproof. It is well worth the money. The best part about it is that you can do direct drive no worrying about chain slack or alignment. Also if you need quicker shifting you can mount a pneumatic piston to rather than the slower shifting servo. Another cool feature is the built in encoders. All this in five pounds. Here is the site - AndyMark
High Ratio - 11.8:1
Low Ratio - 30.1:1
I do have the footage; I will have to post it. I can tell that we went all the way to the finals and got second place.
Disadvantages - Not as durable as most wheels, the little wheels on the Omni wheel sometimes fall off (To prevent this use lock tight on the bolt the fasten them on.) A lot more vibration than a pneumatic wheel. Very low coefficient of friction.
Advantages - Turn on a dime, works on carpet, easy to repair, even if a small wheel falls out you will still be functional
Why did you combine them with a traction wheel - Omni wheels alone do not have enough traction to push around other robots so that why we use traction wheels in the back. Also if you are using tank drive and you try turning with all traction wheels the front wheels will get caught up on the floor.
Programming Omni wheels - We use a system called tank drive; rotate the right forward and the left wheel backward and you turn left. It very easy to program. Here how we programmed it -
This year the initial fifteen seconds of the 2.5 min match was autonomous. This was a little different then past years though, FIRST (For Inspiration and Recognition of Science and Technology) supplied all the team with an IR sensor. So when our robot was driving the course autonomously you could have semi control over it, they called this hybrid mode. This meant teams were using super power remote controls with custom IR LEDs and using filters to block out all the other noise.
Due to so much IR noise we decide that it would be better just to rely on our encoders. These encoders counted the rotation of each wheel and by count you would know the distance you traveled. Although in past years we use CMU cameras to lock on a colors and gyro chips.
