Stop Sign Drive

Hey all!

So I have been experimenting with different drivetrains and I had a crazy idea. What if you had 8 motors arranged into a stop sign configuration. Like two x drives combined with one another. Could this work? I wouldn’t use it for competition since it would be a huge waste in motors, but I still want to make it anyways.

One reason I think it might not work is that since this is really just two x drives offset by 45 degrees, there may come issues of force. I know that x drive can at times be the square root of 2 times faster than your standard 4wd, but at other times it will be slower. If the two are offset in this way, could issues arise?

Thank you so much de geso!

Wow that’s a bright image…

This can work and I’m pretty sure someone here has done it (or at least I know its come up a bunch).

You must slow down the not angled motors. My holonomic code plus some simple + code modulated by the difference between the angled motor speeds, in the X and Y direction respectively will probably work decently well.

Unfortunately you’ll never get that 40% power on the not angled back.

I’ve deleted one message from this thread for being off topic.

Thanks Karthik

Wait is that true? I was thinking you would have to slow down the angled motors since the + motors wouldn’t be able to catch up? Could you please explain why that is?

Yes, you are correct. When spinning in place, all 8 wheels should be driving at the same speed, but when driving forward/backward, the angled wheels at the “corners” would need to drive ~29% slower in order to cause the same net velocity vector as the wheels on the left and right sides. Similar for strafing left or right. However, when driving at a 45 degree diagonal, the opposite would be true. Because now, the wheels at the corners essentially become the wheels at the sides, and vice versa.

However, none of this is actually necessary, and you could simply drive all the wheels at the same speeds if you don’t care about some wheels being dragged along by the others.

By the way, a thread about this drive design was posted just two months ago:

Thanks guys for all the help by the way de geso!

So would that really be an issue if the wheels are being dragged? Couldn’t that actually be an advantage and make it move slightly faster than if you reduced motor power? Also suppose the robot is moving a heavy load, wouldn’t that additional power help to get the job done?

Thanks for the link by the way!

An octogon asterisk drive may work.

And yep. I am bringing that design back from the dead. :smiley:
Asterisk drive is back. :wink:

The links no longer work but here is the thread if you care

I got that backwards, sorry.

No, I doubt it would actually cause much of a negative effect. Yes, obviously slowing down the motors through software is not desirable from a power standpoint. So yes, if you do plan to slow some motors to prevent other wheels from being dragged along, you may wish to have a toggle to disable that feature to be able to use maximum motor power.

I think you’d be better off power and speed wise to just double up an X drive’s motors.

The corner wheels are approximately 1.4 times faster, and have 0.7 times the power. Because you’d have to divide the power supplied to the corner wheels by 1.4 to get them to go the same speed as the wheels facing straight, they are now at 0.5 of the power (0.7 already reduced power/1.4 to match the speed of the wheels facing straight). There are four corner wheels adding up to 2 forward facing wheels of power, plus 2 more motors of power from your front facing wheels, making for the equivalent of 4 forward facing motors of power. The speed, because the corner wheels were slowed down to match the forward facing ones, is the speed of a normal base.

If, however, you use all 8 motors on the corners, you have 0.7 times the equivalent forward power on each motor, meaning 1.4 times the power on each wheel because two motors per wheel. Multiply that by four wheels and you have 5.6 times the power of a single forward facing motor, the equivalent of 1.6 extra motors relative to the stop sign, and without sacrificing speed.

If you just want to make a cool base, I advise trying something like this, because it’s just awesome