Re: Help with Omni wheels?
 

Our team used two omniwheels in the front and two driven traction wheels in the back. The only problem with it was we could not get the omnis to stop turning when we wanted them to. This resulted in the front of the robot continuing to spin after we expected it to. Also, although they were very manuverable, another disadvantage that it was nearly impossible to go straight.

Re: Help with Omni wheels?
 

thanks for the help that will definately help our plans

Re: Omni wheels?
 

WE shattered a junky plastic one all over the field tw years back... and another one demonstrating post-season. The ones currently on the robot aren't very "omni" as most of the small wheels are locked in place by what I assume is a crushing force of the omniwheel plastic colapsing.


That said, last year we used these: http://andymark.biz/am-0097.html
with excellent results, and we will use them again in the future...

Re: Help with Omni wheels?
 

I wouldn't say mecanum wheels are better than omni wheels, they are quite different and transfer power differently to the movement of the bot, but I wouldn't call them better, I find the biggest thing about having a strafing bot, is to make sure your driving practices, and uses all the advantages the wheels give you (too often do I see a bot with mecanums or omnis being driving like a 4wd bot, I dislike it lol)

for the record omni and mecanums have slightly different pros and cons about them and depending on how you want to drive it or how skilled your driver is at controlling them, ethier one could seem "better" than the other for your team, I personally perfer omns over mecanums!

Re: Help with Omni wheels?
 

Driving Straight is definitely possible with omnis. Arc turning with two back omni can cause your back two omni wheels to fishtail moderately making the robot more difficult to drive. FRC#494 in 2006 used omnis in the corners instead of two omnis on the back side to help control fishtailing. Read the full report on page 160 of the 2006 FIRST Robotics Book.

Re: Help with Omni wheels?
 

It sounds like you might have the center of gravity of your robot too far forward for easy controllability. Putting it closer to the traction wheels would help things a lot.

When I joined the TechnoKats as a mentor, my first real programming challenge was to compensate in software for exactly this situation. The code detected the rear wheels' rotation (Banner optical sensors pointing at alternating reflective/nonreflective sections of hub) and adjusted the relative power to the left and right side motors in order to keep the wheel speeds consistent for perfectly straight travel.