2 vs 4 motor drive

#1

I have seen threads that say 2 motors are better than 4 motors and the opposite. My team and I have gone back and forth trying to decide which is better. What do you think?

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#2

If you plan on being competitive, I would 100% go with a 4 motor drive. 4 Motor drives are much faster and enable you to push other robots around without having to worry about your drive overheating. If your main concern is having enough motors to do other functions on your robot, you might want to consider a less complicated design that can power all subsystems with 4 motors.

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#3

I would strongly recommend a two motor drive if you wanted to focus on what your robot is doing, and not as much on movement. The advantage to a four motor drive would be that it easier to build and the above mentioned advantages by @ben.starkman. Although, I believe that you can make a two motor drive go fast depending on your gear ratio (I don’t recommend chains for drive systems) and as long as your gear ratio is not insane (example, a theoretical 4 inch gear turning a .25 inch gear or vice-versa), you should not expect any problems.

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#4

why would you not suggest using chains? Just interested, do they have a drawback I haven’t seen yet? Also, what would I use instead?

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#5

I’m not sure where these 2 motor drive lovers are coming from, but I don’t see how you can make a competitive robot without having at least four motors on your drive. Not even coming from a defensive standpoint, you will want the extra power as a quality of life improvement, as well as being able to go a lot faster and not having to worry about your drive motors burning out, as they WILL on a 2 motor drive. Robots will inevitably be heavier this year, not just due to the weight of lifts, but also the .6 lb cubes that you will hopefully be hauling more than one around of at a time. 4 motor was the only competitive drive option for turning point, and I don’t see how 2 motors can ever be a viable choice, no matter the game. Making your scoring mechanisms on 4 motors should be relatively easy, considering the amount of passive/dual purpose mechanisms shown off in turning point.

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#6

The downside of chains is that they slightly increase friction, and can possibly break, effectively breaking your entire drive. Many teams have opted to use the lower friction, more reliable, but more complicated gear drive setup, myself included.

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#7

3 motor drive. Two motor front and 1 motor back.

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#8

My experience with chains was that in some cases, you could not get the exact size you needed, a chain that is even slightly too long could slip, and if it is too short, there could be problems with the wheels turning properly.

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#9

Really? I’ve never had that issue before?

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#10

I did. My team (turning point) originally tried to use a chain to connect some gears in our two motor drive and it did not go so well.

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#11

Another big problem with chain is that you will slow down by 20 to 30 percent, compared to having a direct drive that get 100 percent of the speed out of the motor. We had this problem last year and it slowed us down a lot.

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#12

You are generally supposed to tension chain such that it is perfectly tight the perfect tightness. In order to minimize friction you should use free-spinning spacers or 6-tooth sprockets for this

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#13

I think you guys have had the chain a little too tight. I prefer to not use it too often, but you always want to have a little slack to keep it from adding too much friction.

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#14

With our chain, we had the size down to either adding or removing a segment, each would not work and there was no “just right” for some reason (probably just the distances not working out). But chains are great for when mounting a bunch of gears is not going to work out.

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#15

That is why you add tensioners- in order to modify the distance the chain travels

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#16

One link shouldn’t make that much of a difference. Maybe the two items you had weren’t quite lined up causing it to slip off easier.

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#17

Sounds about right.

(20 characters)

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#18

Distance could play a factor too. How far was it?

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#19

I think you replied to the wrong person lol

Anyway, to steer this back on topic, here’s my two cents:

A two motor drive will rarely if ever be viable competitively. There simply isn’t enough torque to support the weight of most robots at competitive speeds, and it will make autonomous much harder due to its weak influence on the bot’s momentum. A three motor drive could certainly work but requires a unique bot design in order to pull off- specifically a central wheel. Also remember than this won’t help you when turning, so with this setup you will probably need a fairly wide chassis.

Four motors is ideal and I highly recommend that you do everything you can to make it work.

On the topic of chain, it is usually perfectly acceptable to chain your drive. If you can avoid it, direct drive is obviously better, as it is true that chain introduces friction. However, properly applied chain, in nearly all cases, will not have a noticeable effect on a drivetrain. (This is not true for everything- chain is usually a pretty bad idea on a flywheel)

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#20

Keep in mind that a 2m V5 drive gives off as much torque as a 6m turbo drive.

Teams have been successful in past years on v4 bots, so long as you don’t have noticeable friction and you don’t care about defense i’d say a 2m drive is definitely viable

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