What do you guys think is better for a competition robot that is 15 pounds. 4 regular wheels vs. 4 omnis. What are some disadvantages and advantages, such as will we be able to turn with all regular wheels? Will we be easily pushed with 4 omnis?
Do you want everyone to review the Thread, Dynamic pull test with Mecanum wheels, before answering??
I would think 2 omnis and 2 high tractions would be best. Personally, i believe sideways motion is extremely critical in this game. So if you can easily be pushed sideways, then you’ll have a lot of issues. However, using pure traction wheels on a 15 pound robot can be problematic. Typically, the turning scrub is too narrow, preventing robots from turning. Combining the 2 wheels will then create better turning scrub, yet good traction from the front and back(due to omnis) and sideways(due to high traction)
Use 4 powered omni wheels and put two unpowered normal wheels in the middle of the drivetrain at the the center of rotation. This way, you will have no trouble turning because of the omnis, won’t be pushed because of the traction wheels, and will have your center of rotation at the center of your robot. (It would be on one side or the other with 2 high traction and 2 omnis). I think you would have a lot of trouble turning with all normal wheels, and you would get pushed sideways easily with all omnis.
Owen, with the drive that we have we can do exactly what you are saying, but will the drive be able to go over sacks, without the center wheel being powered?
Why not power it too? Chain and sprockets…
If you want to use high traction wheels, I’d agree with Owen on this one. Force the center of rotation in the middle of your robot so it’s easier to drive/program.
When you turn on the mat with 4 wheels, the wheels are forced to “skid” across the mat, so omni wheels naturally skid easier because of less friction to go side ways, while high traction wheels will result in ALOT of friction while skidding
Similar to our offensive bots drive, I think a good bet is to do a 6 wheel drive. Use traction wheels on the center and omnis on the outside.
We are actually doing a mecanum drive with traction wheels where the 2 other wheels on a 6wheel drive would go, unpowered for weight distro issues.
And seeing as we’re using mecanums, we opted for a VERY low to the ground drive. Any sacks in our way will be pushed to the side or intaked.
This.
We have found that if you use solid wheels on the front of a robot, turning away from the sides of the field is not intuitive, and with solids at the back, I find that most intakes are too far from the centre of turning, but it is mostly a personal preference thing. Six wheels with a turning centre in the middle give a nice balance, and stops you being pushed sideways. Lack of any sideways friction can also result in robots drifting sideways in autonomous too, so something to watch out for.
~Matt.
I’m confused. How is the mechanum drive going to work if you have traction wheels as well?
Also, we have used many different combinations. Our first year (Elevation), we used traction in the back, omni in the front. Then our second year (Clean Sweep), the robot I started out on (24A) had an “x” holonomic drive, then was the true birth of 24C, and we ended up having an “h” holonomic drive, using 5 omni wheels. Our third year (Round Up), we went a bit all over the place. Started out with traction in the back, omni in the front, then switched to a tiny “h” holonomic drive (seriously the smallest drive I have ever built, and it used 4" wheels), and then went to small traction in the back, small omnis in the front. Then in Gateway last year, we had omnis in the front, omnis in the back, then switched to small omni wheels in the front and back, having two small traction wheels in the middle, which were both not powered. Finally, this year, we started out with 6-wheeled all omni, all powered, and now have switched to 4-wheeled all omni.
After all of that experience, I have to say that having the small omni wheels on the front and back, with the small traction wheels in the center was the best drive we ever had. I absolutely loved it, and so did the rest of the members on 24C. However, this year we planned to drive over the sacks, so if we were to do a similar drive, we would want the middle wheels to be powered. We also wanted to have 6 motors on the drive again, and as we found in Gateway (and with our first drive this year), 6 motors to 6 wheels isn’t very easy.
I say, the more omni wheels you have powered the better (okay, okay, I think 4 is enough, AURA), and if you want to, add a pair of traction wheels.
~Jordan
If you’re using tank drive, there’s no reason not to gear your wheels together to power that center wheel. Gearing wheels together makes your drive so much more efficient, and better at pushing other robots. We did that for Gateway (6-wheel drive, omnis in the front and back, traction in the middle, all wheels powered) and our robot was very good in pushing battles.
Just an update. We have tested all configurations of wheel types on our robot. We realized that best turning is the 4 omnis. Though we can get pushed, for this first competition (10/13) we are going with 4 omnis, because i doubt there will be much defense at the first competition. For the next competition (10/20), we will make a 6 wheel drive.
My memory could be failing me… but i would think there would be more defense because most robots have issues in the first competition…
I agree. I actually made a mistake when writing my last post. In Gateway our last drive had only the two middle traction wheels powered. The outer 4 omni wheels were not powered. The reason we did this was because we were too lazy to shave off the outer plastic of the 15-tooth tank tread drive wheels that we were using geared to 6-tooth sprockets.
The new drive we are in the process of building for Sack Attack will be the same wheel configuration as that, but will have all six wheels powered, running off of just four 393 motors, geared 1:2 for speed.
~Jordan
Do Omni wheels hold less weight that standard wheels
Dude, this thread has been dead for six years. Don’t revive dead threads.