X-holonomic question

Hi,
I have never done an x-holonomic to test it before, but I’ve tried a few things and I couldn’t really figure this out. How much less power would a x-holonomic have compared to your standard tank drive? For example, if a tank drive could carry 10 lbs. then how much could a holonomic carry? I’m pretty certain it is a bit less considering the angle the wheels are mounted at and that they fight each other to a certain degree.
I know it varies with ratios and such so for the purposes of this question let us assume that the tank drive is four 393s set to speed direct dring four omnis, and the holonomic is perfectly built, also with four 393s set to speed direct driving four omnis.
Not sure how well I worded that…

Here is a helpful post from AURA.

http://www.aura.org.nz/archives/1137

Well power wouldn’t change.
This really gets into the math behind it
https://vexforum.com/t/shifting-x-drive/21600/1
but think of an x drive as a 1.41:1 gear ratio so .7 times the torque of a tank drive.

I’ll link you to an article over at AURA’s website, which is very informative about differences in torque/speed of an X drive.

http://www.aura.org.nz/archives/1137

The main idea is that an X drive is faster than a tank drive (sqrt2 times as fast) whereas a tank drive has more torque than an X drive. (sqrt2 times as much torque).

I think having an X drive on 4 inch omnis with speed motors would be pushing it unless your robot is very light, as that is essentially equivalent to a:

1.6 * sqrt2 = 2.263

1:2.263 ratio on tank drive, which is REALLY fast and doesn’t have much torque, and would probably be likely to overheat. If I was going to make an X drive with 4 inch omni wheels I would personally keep the motors on torque.

EDIT: Oops, looks like I got ninja’d by SweetMochi on the article…

EDIT 2: I also have a gut feeling that a lot of torque/speed will be lost as friction when using an X drive, but to my knowledge no one has tried to get any empirical evidence for it, so I can’t be sure.

Thanks to you two for pointing out that article. So, basically if the motors were in torque mode on the holonomic, it would be equivalent to a 1:1.4 speed ratio on tank with the same amount of torque? Or is it less torque?

It would have the same amount of torque as a tank drive on a 1.4:1 speed ratio logically. In practice this may not actually be true due to friction in the omni-wheel rollers etc. The best thing I can do is encourage you to try both out, and share your findings here if you come across anything interesting :D.

Well x-holonomic has 0.707 times the torque of a tank drive.

If you switch to torque mode that gives you 1.6 times more torque and 1.6 times less speed.

0.707 x 1.6 = 1.131
1.414 / 1.6 = 0.884

So if you run an x-holonomic with torque motors you will have 13.1% more torque and 11.6% less speed I believe?

So… are you saying if both the tank and holonomic were on high torque the holonomic would have more torque and less speed than tank? But wouldn’t it be more speed and less torque?

Well, right now we are on tank and it’s been doing very well, but we want to switch to some type of holonomic.

Well if you switch both the x-holonomic and the tank drive to torque then the same rules apply as if they are both on speed. I apologize for the confusion, I thought you were asking about if you switched the x-holonomic to torque and then compared it to a tank drive on speed.

Ok, that makes much more sense. Thanks for all your assistance everyone.