Chief Delphi - What r possible drive systems under these circumstances?

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Re: What r possible drive systems under these circumstances?

Quote:

Originally Posted by Cartwright (Post 790554)

However, It is important to point out the specific case of multi-wheeled robots or robots with multiple contact patches between the wheel and the surface. This is what this engineering book I have says: If the normal force is increased, per given area of contact patch, the COF decreases. As the normal force decreases, the COF increases. If this were not true, then lowering tire air pressure in cars or installing wider tires, which both increase the area of the contact patch, would have little effect on traction.

The traction force is equal to the acceleration times the mass. Therefore, wouldn't the wheel's contact patches matter?

I think it comes down to material on material here, Rubber on assfault, is different then <Insert plastics name> on <Insert same name>.
Correct me if i'm wrong

Re: What r possible drive systems under these circumstances?

Quote:

Originally Posted by Tanis (Post 790338)

I could be entirely wrong, and with some of these ideas it will be hard to tell until a prototype is built.

However, I don't think that the swerve wheels would get enough traction to change directions, or turn effectively.
Imagine having a three wheel set up, for example, with the back two wheels being powered by CIMs, and the swerve wheel turning via another motor. If you rotate the robot right, the try to quickly change directions left, the robot will probably keep going right for awhile before the wheel finally "catches" or grips the floor.

I'm seeing this response a lot in relation to swerves. Say we go with a 118 style crab: All wheels steered together. Even with the type, the wheels don't suddenly make a 90 degree turn, or however much people assume. The robot will (assuming that it's driving) turn in an arc. The cleanness of this arc is a factor, but not enough to disqualify the design. Unless you're using some odd turning system, the wheels won't change direction faster than the robot can adjust.

For the sake of the point, now let's move to sets of 2. The front wheels are now steered separate of the rear. With a bit of programming, and a big red button, you now have the option of an AWD 4 wheel steering system or a standard crab. Say we drive each wheel independently, this opens up even MORE options. We can drive normal crab, normal crab with traction control (I mean, seriously, the Jaguars have built in current sensors! It's not THAT hard to do!), 4 wheel steering, 4 wheel steering with slip control, 4 wheel steering with Yaw control (see the Modern Subaru STI and Mitsubishi EVO for this), and more. Plus, at the hit of a button, we can move (in a short amount of time) from moving forward and steering to side strafing. We've got traction control already, so what's to stop you from using a gyro to even out the direction of the bot? Sure the trailer's going to weigh you down, but a bit of time spent in testing, and a decent programmer makes that problem nonexistent.

Personally, I don't see any other drive system that has more available to it than a 4 wheel crab with independent power. You can do almost ANY form of driving you need.

Re: What r possible drive systems under these circumstances?

Quote:

Originally Posted by CraigHickman (Post 799040)

(I mean, seriously, the Jaguars have built in current sensors! It's not THAT hard to do!)

That we can't access this year!

In all seriousness though, I do agree with the rest of your post. My team will not be considering crab drive because we don't have the resources or experience to make one, but I do believe that there will be advantages to building one this year.

Without testing I'm not sure if these advantages are worth the weight and increased complexity, but I would definitely believe it if someone that had done testing or with more experience thought it was worth it.

Re: What r possible drive systems under these circumstances?

I am in the process of designing a 20 wheel drive. :)

Re: What r possible drive systems under these circumstances?

Quote:

Originally Posted by Cartwright (Post 790554)

In perfect physics, contact area has no relation on total traction force, which is just coefficient of friction times normal force.

In the real world, things like rubber on asphalt or roughtop treading on carpet are different, because they have some measure of "interlocking" between the wheel and the carpet, as none of the listed things here are perfectly flat and smooth.

However, the playing field surface this year is probably about as close to perfect physics (friction wise) as we'll ever get in FRC, because there isn't any "interlocking" between smooth acetal wheels and nearly smooth FRP flooring.