# 8 wheel omni base - Octomni!

Has anyone built an eight wheel drive base using omni wheels? Not doubled up omni’s but one on each of the eight sides of the base.

I think I have the drive code worked out and on screen it looks like the force loads will be fine. But before I invest on this new ground breaking design I thought I’d check and see if someone else has done this and their results.

At least your speeds will be evened out forward, reverse, and at 45’s

How do the different wheel speeds work out? Wouldn’t your corner wheels move you faster than the side wheels?
Is the only advantage over an x-drove that you can use more than half your motors when going diagonal?

Sounds cool! I’ve never seen a true octonum with 8 independent wheels, only the “butterfly” configuration of 8 wheels with an omni/traction pair in each corner, as in this video (drive base at 1:25).

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7580A did a 6 wheel version of this but the concept is essentially the same. The math for matching the motor speeds with different orientations and wheel sizes is on the forums somewhere.

That’s the closest I’ve ever seen to what you’re talking about. They did find that when turning and moving diagonally, some adjustments had to be made to the drive code so that the wheels could run at the same speed.

If you do field-centric holonomic you are typically using the angle in the calculations. So adding offsets of the angle for each motor on the 45’s is pretty easy as it is just another offset to add in.

For competition, robots doesn’t that leave just two motor ports as each of the 8 may have a different signal and can’t use a Y splitter?

This would definitely be possible and it has some advantages. The direction with the least torque has more torque than the direction with the least torque on an 8-motor X-drive, for example.

There are good reasons why you don’t see teams doing this, though.

It’s bad to have your motors in conflict with each other. An X drive naturally wants to go faster than a tank drive. If the octagonal drive is moving in the direction of one of its eight sides, then it has both tank and X components. So the X drive has to slow down so that it moves at the same speed as the tank drive, otherwise it will be trying to drag the tank drive forward which will mean the X motors draw an unnecessarily high current.

You can try to adjust the motor power values in your code to compensate for this, using an experimentally measured function relating motor power to speed. But this function could be different under different torque loads, and you don’t know how much torque the motors are under unless you have sensors.

So with an encoder on each of the eight wheels and some pretty complex code, you could set this drive up so that the motors weren’t in conflict with each other while driving. But even then, the robot is only as fast as its slowest set of wheels. Because of the way the wheels are arranged, you can never run all of your drive motors at full power - in every direction some of the wheels have to turn with reduced power so that other wheels can catch up.

I think there are applications where this design could be useful, but unless something extraordinary happens I don’t think VRC is one of them.

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BNS had that drive for skyrise on their big bot, I remember.

OK, so you have to slow down the corner wheels; that’s what I figured. In that case its pretty much a waste of motors.

I thought they had an 8 motor x drive

They didn’t… It was an 8 motor 4 wheel holonomic.

while i imagine keeping maximum sideways speed would be difficult with an 8 motor drive, what is keeping teams from gearing up the middle motors on an asterisk drive to keep the correct speed?

I’m sorry… my fault. Didn’t read the title carefully. I apologize for that. Now back to normal discussion – It would be pretty cool I assume?

It does and I’m just going to put two red or blue flags out on arms and wave them. The opposing alliance will be so enthralled with the drive train that they will forget to drive and win the game. :rolleyes:

I’m just messing around with drive bases since I have some time on my hands…

Last week I put the “legged” wheels on an IQ robot. (Basic claw bot, I offset the wheel hubs in the rear to clear the front legs). It was pretty cool since the IQ part is so small. I forgot to get pictures, so I may need to reassemble it.

The 8 omni code has the “outside wheels” going slower, so I don’t think it will be faster than a 4 omni.

Can someone from BNS confirm they had a 8 motor 4 wheel drive?

And you know when the new A-72 based system and the new micro H bridges, 16+motors is in your future. :rolleyes:

7580A did the equivalent of gearing up by using a larger wheel for the middle motors.

What’s the pros and cons of using different number of wheels? My school has been using a standard 4 wheel chassis for many years and we were wondering if having different number of wheels for different situations could help our robot performance.

Most teams use four wheels; it’s pretty simple and standard. If you can afford 6 motors for your base this year, though, you might want to use 6 wheels so each can direct drive its own wheel.

Yup. Both our spare 15 inch robot(Gypsy Danger) and our 24 inch robot(Lucky Seven) had 8 motor 4 wheel X drives.

Coolness factor. 3 2 1 GO and you roll and the other team just stops and stares for the next 2 mins going; “Wait, what, does that work? How does that work? That’s really cool? Can we build that? We should build that” and suddenly its’ 3 2 1 STOP’ and you’ve won.

And I’m pretty stunned that I’m back in a thread from 4 years ago

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We really shouldn’t be reviving an old thread. Making a new topic and linking this one would be better. @DRow time to initiate the Code Red Lockdown Thread!

Yep, but Google and the local search is your friend, lots to be found out in discussions that are much newer.