What r possible drive systems under these circumstances?
 

Okay so basically the game contradicts itself. Slippery floor, slippery wheels. We actually had the polymer "regolith" in our room..it was used in one of our bathrooms. At first when you move your hand across the surface it feels very bumpy. But when we moved the wheels across the surface there was O friction, a concept that is hard to imagine unless you actually try it out for urself. It comes down to who has a good drive system.....which is?
Also for those who who still need help trying to figure out the substance...it is a polymer..glass liner is what it is called..it is used for bathroomwalls..not sure if it is at home depot.....

Re: What r possible drive systems under these circumstances?
 

Since I have no experience with the material, or much insight into friction and traction, I will list a brief summary of available options.

Wheels-
2,3,4, and 6 are all possibilities I believe we will be seeing. From what I have been hearing, 6 will be far more popular than past years.

Drive-
Arcade, Tank, swerve, [4wd], [2wd].
Coming from someone who lives in a snow- and ice-plagued area, front wheel drive will probably work better than rear-wheel, with all-wheel being ideal. I would definitely not recommend swerve drive this year.


You are correct that it is more limited than past years, but there are still plenty of options.

Re: What r possible drive systems under these circumstances?
 

. . Any thing your Imagination can come up with!!! . . as long as there isn't a rule against it.

Re: What r possible drive systems under these circumstances?
 

i would say, that having FWD with rear wheel steering(if not AWD with front wheel steering) would be good, because you can use the brake feature on the jaguars to lock the wheels

Re: What r possible drive systems under these circumstances?
 

I was thinking of balancing the robot on two drive wheels and letting the trailer keep it up right and than steer the drive wheels and if you angle the rear bumpers out to not allow the trailer to pivot. Doing this instead of driving a car with a trailer you are driving a pick up truck.

Re: What r possible drive systems under these circumstances?
 

Tanis said: Why? (My team is considering a swerve drive -- any advice I can take back to them would be a helpful addition to the discussion.)

Re: What r possible drive systems under these circumstances?
 

Front wheel drive vehicles are only better in snow because the engine is locaed over your drive wheels therefore the force normal is greater in comparison to rear wheel drive where there is far less weight on them. Hence its not a matter of front wheel drive or rear wheel robot but a mattter of weight distrubution

Re: What r possible drive systems under these circumstances?
 

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.

Re: What r possible drive systems under these circumstances?
 

The only possible successful drive system with the rules worded as they are is a controlable drive system. The momentum of a 100lb robot at 10ft/s is too much to accurately turn in such a low friction environment. So for the strategy we've laid out, we're looking at a max of 7-8 ft/s depending on the system of turning we choose.

To all you speed mongers out there, good luck :cool:

Re: What r possible drive systems under these circumstances?
 

To speed mongers K=.5mv^2 :ahh:

Anywasy the best drive train will most likely be the one that zamboni's use becuase well, they got what 50 year of engineering behind them, so why try to reinvent the wheel in 6 weeks (don't answer that).

Re: What r possible drive systems under these circumstances?
 

Unless I am mistaken, Zambonis just use a typical car drive (front wheels rotate, rear wheel drive).
I believe they get most of their traction from the type of wheel, and the size (their wheels are very wide), and the fact that they go very slowly.

Re: What r possible drive systems under these circumstances?
 

A Zamboni has car steering and snow tires right? It also has a massive water tank between the axles.

As for swerve drive, the stereotypical lack of grip will not likely be a problem this year. Assuming that all wheels are driven, a robot's MAX acceleration is the coefficient of stiction (mu) times g (a=mu*g). If the robot isn't AWD, then weight distribution becomes an issue. The equation mentions nothing about a robot's mass or the wheels' contact patches. Those two become important in pushing matches.


It seems the options are sill wide open!

Re: What r possible drive systems under these circumstances?
 

The type of drive train you use isn't as important as how you incorporate it into your strategy. A four wheel drive can be just as effective as a crab drive, which can be just as effective as an omnid style drive, if used properly. Certain designs may have better potential, but I feel that it is more important that what you make works well and the robot is designed as a whole. If your drive system works well with your manipulator and your game strategy, then you can be very successful. If not, you could have the best drive train in the world, but it is useless if you don't have a game plan or a manipulator to take advantage of it.

Re: What r possible drive systems under these circumstances?
 

In the past we have always started our design at max speed and worked from there.
I am not sure if top speed is the correct way to approach this problem. It seems that the CIM's will provide more than enough power to spin the wheels.

If we determine the amount of torque needed to spin the wheels and design the gear ratio so that max torque at the 40A level is about the same as the amount of torque needed to spin the wheels, then it would be harder for the driver to cause wheelspin. In this example the driver would have to move the joysticks to full power to cause the wheels to spin.
I think this is the lesson we were supposed to learn from the demonstration that Dean and Woody did on the playing field.
If you design for a low topspeed, there will be a lot of torque available with just a small movement of the joystick and it will be very easy for the driver to cause the wheels to spin.

Am I way out in left field here?

Re: What r possible drive systems under these circumstances?
 

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?

Re: What r possible drive systems under these circumstances?
 

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?
 

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?
 

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?
 

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.