4 vs 6 wheels (what to choose)

[HarveyAce]

We in team 3329 are apparently still in the process of choosing our drive system. We are debating 4 or six wheel drive, and I am leaning toward the 6 wheel because of the balance and weight distribution of our robot, especially if we are planning on making something to reach up to the top pegs. are those factors to take in with the selection of the number of wheels? It also may help to let everyone know that we are using almost the same design layout for the chassis as the kop, but we are re fabricating it in 1/8 in aluminum box tubing, because we had issues last year with the c-frame warping, and our robot was EXTREMELY light last year. So 4 or six?

[Chris is me]

Originally Posted by nckureghian14

Cons: Lacks ease of maneuverability

Does it now? I've seen hundreds of six wheel drives and they all seemed maneuverable to me.

I'm tired of people essentially saying "since mecanum is more manuverable, 6 wheel drive must be significantly less manuverable". Strafing does not equal manuverability, or vice versa.

[MattC9]

Originally Posted by Chris is me

I'm tired of people essentially saying "since mecanum is more manuverable, 6 wheel drive must be significantly less manuverable". Strafing does not equal manuverability, or vice versa.

...you have no idea of how much i have to fight this...

[548swimmer]

I'd say 6 wheel rocker. With the rock you don't have to worry about "skipping" during your turns.

[BrendanB]

Originally Posted by 548swimmer

I'd say 6 wheel rocker. With the rock you don't have to worry about "skipping" during your turns.

I second this idea. 6wd with the center wheel dropped 1/8 of an inch, and if you are using the kit frame the center hole is already dropped 3/16 of an inch.

[EagleEngineer]

"Cons: Lacks ease of maneuverability"

We actually did a test, and realized that the 6-wheel drive is actually more maneuverable than the Mecanum.

[BJC]

I will agree with the others: 6 wheel drive.

[Team 2811]

Originally Posted by nckureghian14

Pros and Cons:

4 Wheel Mecanum

Pros: Maneuverability

Cons: Slower

Not true. My team had a four wheel mechanum drive train last year and it was really fast in every direction. However, it is true that going straight is faster than going in a different direction.

[Team 2811]

I would say mechanum because that is what our team is using and it works really well but the 6 wheel has really go maneuverability too if you implement the drive system right.

If you use 2 rubber wheels for friction as the two center most wheels and then you use omni wheels for the front 2 and back 2 then you have great maneuverability and better control. However you aren't as maneuverable as with mechanum.

With the six wheel drive train, you have a better resistance from being pushed. My experience shows that the mechanum can be pushed if you have a weaker but faster gear ratio.

Hope this helps

[Teched3]

IMO, mechanum is a difficult task in programming during the build season, even for very experienced teams. Stay within your capabilities. Wheels are available through AndyMark, so the mechanical requirements can be met if you have the funds. Use the offseason to develop new systems and concepts. I have been in this fo 16 years, and am still learning. Just my opinion.

[Grim Tuesday]

You can't strafe with 6WD, you have to tank drive, which if hanging pegs, involves backing up, then turning, then going back.

[apalrd]

Originally Posted by Grim Tuesday

You can't strafe with 6WD, you have to tank drive, which if hanging pegs, involves backing up, then turning, then going back.

Not if you align to the pegs while approaching them, and not after you hit them.

Many people around here seem to be saying "oh, oh, a mecanum is sooo much more maneuverable, omg" when a well-driven 6wd can do everything except strafe, and is easier to build since everything comes in the KOP (and slightly easier to program, although the WPIlib has mecanum code for you)

[AustinSchuh]

Originally Posted by Grim Tuesday

You can't strafe with 6WD, you have to tank drive, which if hanging pegs, involves backing up, then turning, then going back.

If you are within about a foot of the peg, which any respectable driver will be able to do, you can just turn in place and that'll fix any misalignment...

[NyCityKId]

My team is trying out mecanums for the first time this year... mostly because we thought the wheels looked really cool (joking). But really, I've seen a few threads on this forum about 6 wheels vs 4 wheels and I think the problem is that we need to define what maneuverability is once and for all for the purposes of FRC robots. If maneuverability includes strafing then obviously 4 wheel mecanum drive wins, however if u say maneuverability is the ability to have as much control over the robot as possible and get from one point to another as fast as possible and with control and you exclude strafing then the six wheel drive system would be more maneuverable (provided you have some method of preventing the front and/or rear wheels from skipping). All drive trains have they're pros and cons and it comes down to your knowledge of the different type of systems, how you plan to implement the system and your team's strategy for the game.

[PAR_WIG1350]

Maneuverability should be expressed as a quantity of degrees of freedom and the respective qualitative measurements for each. Each degree of freedom is either translative or rotational. Translative measurements should be rated based on acceleration and breaking, in terms of the length (distance) and/or time required to get up to maximum speed from a dead stop, and to stop from maximum speed. Rotational axes should be rated based on angular velocity, and minimum turning radius.

Maximum translative speed is irrelevant to maneuverability (in my opinion) since maneuverability is about controllability, not speed. Acceleration, on the other hand, provides information about how much space and time is required to change directions, which is directly related to controllability. Angular velocity is important since a robot that turns too slow wouldn't be able to react quickly while one that turns too fast would be hard to control.

Even with these measurements, there are still so many factors that are unaccounted for. These really need a little more work.