6WD Pros and Cons

[dtengineering]

Originally Posted by DeepWater

...why would a "rocker" style 6WD inherently have more traction than a "level" wheel 6WD?

I am wondering if a "level" 6WD with omnis on only one end would be a good compromise?

There is no inherent traction advantage for a rocker robot over a level robot, until you consider the wheels.

If the level 6wd robot had omnis front and back (which tend to have a lower co-efficient of friction than traction wheels) then 2/3 of your weight (assuming a centre of gravity over top of the centre axle) would be transmitted to the ground through the low-friction omnis.

In a "rocker" set up, if all the wheels are traction wheels, then 100% of the robot weight is transmitted to the ground through high-friction wheels. Therefore you have more traction.

Two years ago we built a 6wd robot that was pretty good at pushing, and climbing using the kitbot frame (with lowered centre axle), 6"x2" IFI traction wheels, and two CIMs per side driving the 12:1 KOP gearbox, further geared down by the sprockets driving the wheels to give a max speed in the 6-8 fps range as I recall.

We noticed that even with the lowered centre wheel that we had difficulty turning on carpet with six traction wheels. We replaced the rear (heavy side) traction wheels with omnis. Now the front traction wheels were slightly in the air, the majority of the weight (approching 2/3) was supported by the centre traction wheels, and we could turn with no problems. When it came to pushing or climbing, the front traction wheels would often come into contact with the ground, preventing some of the problems of the "flat with four omnis" problems in climbing.

Jason