Wheel configuration

[penguinscanfly]

Our team is using a wide base design and we are trying to decide if we should use six wheels or four. What are some of the advantages and disadvantages of each?

[MrForbes]

The main advantage of a 6 wheel configuration on a "long" robot is that it lets the robot turn.

Since a "wide" robot doesn't have a problem turning with 4 wheels, it's kind of a waste of effort to put 6 wheels on it.

[penguinscanfly]

Thanks for your help! We ended up deciding on four wheels.

[lohsfirst]

Does anyone know whether the "wide" robot tends to oversteer and cause it to be difficult to control since it has a shorter wheelbase?

[Chris is me]

Since a "wide" robot doesn't have a problem turning with 4 wheels, it's kind of a waste of effort to put 6 wheels on it.

Not always. Depending on weight distribution and traction material, a 4WD wide robot *can* have a lot of trouble turning. In Lunacy, many 4wd wide teams, including my own (then 1714), had most of the weight over the back of the robot for improved turning with the trailer. A 2011 wide kitbot we threw together with 4 8 inch wheels turned "well enough", just not as freely and easily as a dropped 6WD. Hence we went with a simpler 6" wheel 6WD wide this year.

Man, I have got to stop posting on CD or my robot will leak out before we post it running!

[Marc S.]

Your robot will turn much better with 6 wheels than with 4. Essentially the shorter the distance between the wheels the better the robot will turn. If your robot is wide it is very easy to make this distance very small, compared to going long. Also consider that a wide robot with 4 wheels has a greater distance between the wheels than a long robot with 6 wheels.

[MrForbes]

The front to back distance is longer, but so is the side to side distance. Look at the proportions of the rectangle formed by the rear 4 wheels of the 6 wheel drive, vs the wheels on the 4 wheel drive.

The 6 wheel has an advantage in that most of the weight is on the center wheels, so the end wheels can skid more easily.

[Chris is me]

The 6 wheel has an advantage in that most of the weight is on the center wheels, so the end wheels can skid more easily.

That's not one to be understated. I think people understate the difference between turning and turning well. Turning well saves your battery, among many, many other advantages, such as general ease of operation, precision, etc.

The whole reason 8WD skids have become popular among the elite teams is because they allow for a more customizable turning scrub while still maintaining ideal traction and different dynamics than a 6WD skid.