# 2 vs 4 motor drive

In an X drive all 4 motors are working. H drive only has 2 motors to move forward, and 1 to strafe.

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Yes but with the wheels at 45 degree angles a little less then half of the power is lost if I am not mistaken.

I believe 1/sqrt(2) power is lost with X drive going forward, while, with kiwi, 1/sqrt(3) is lost. This makes kiwi slightly more efficient

But you gain speed. You can easily rectify that with gear ratios

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I am likely gonna go with a 2m drive with V5. I don’t see the need for a strong drive.

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Here, this is the most important graph to understand X-Drive:

Source: AURA

If you drive forward, backward, or to the side - all four motors are providing power, the velocity is MotorRPM x sqrt(2) and pushing force is 4 x OneMotorTorque/sqrt(2).

If you drive at a diagonal, then only two motors are providing power, velocity is MotorRPM and pushing force is 2 x OneMotorTorque.

Essentially, X-Drive speed is 1.41 times faster and pushing force is 1.41 times weaker than the ordinary tank drive with the identical 4 wheels & 4 motors.

Also, here are the links to the similar topics from the previous seasons: Two motor drives?, X-Drive Speed, Extinct X-Drive?

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You guys simply don’t get it. 8 motor drive is simply the way to go.

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How many ratchets you planning on using?

It was a joke, but you could have 8 motors forward and 4 back and just have 4 functions, though you might have to be a gearing and ratchet wizard.

Or you could even have 4 motors forward power and 2 motors backwards allowing for 2 extra functions

this gave me an idea: ratchets on wheels

I would go with four, just because of the extra power. That way you can get to where you are trying to go without frustration and also build a bigger and heavier robot. Also, with defensive robots being viable options for this year, you will want to have the power to get past other robots, such as wall bots and cap bots.

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This is a common misconception.

If you calculate the speed based on the maximum free-rotating speed, it seems like an X drive would be faster. However, the motors are fighting each other, so they go slower.

The way to consider the math is as force vectors with is where you end up with 1/sqrt(2) .

I was conflating acceleration and top speed. They are not the same. See conversation below.

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What about a 6 motor drivetrain

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As @technik3k posted above, they do lose torque but they also gain speed. With the old legacy motors that may have been true do to them not being able to handle the extra pressure, causing to bog down, but the V5 system has more than enough strength to handle it, and I have seen a standard all omni drive that is directly driven goes to an X-drive and it is noticeably faster.

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Honestly I defiantly see some 6 motor designs popping up. Highly defensive strategies that will probably sacrifice either making stacks quickly or scoring posts quickly.

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X-Drives go faster, but have less torque.A X-Drive is about the same as having a 1.41:1 gear ratio. If you build 4 motor x-drive and a 4 motor base, the X-Drive will beat it in a race but lose in a pushing battle.

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I can see how that might be possible, especially at a light load. It would definitely be the case if the motors were being controlled by speed of rotation. I’d be curious to see the experiment done with a decent sized load.

Based on A = F/M… you know what top speed IS going to be faster on the X drive in a light load as long as the friction is the same. I’m pretty confident a regular drive will have better acceleration. I’d love to see a 12 foot drag race with both drives and a decent weight load.

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I don’t think it’s reduced torque per say - although the effect is the same. The motors are twisting just as hard, but they are pushing at a 45° angle, so force in the forward direction = force × Sin(45°).

Same result though.

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this was a joke I posted a while below, but I’m thinking about it for real now: a 30 pound robot with 8 motors for drivetrain geared to insane ratios. Is this worth it?

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