6 wheel drop center drive train

[bigbeezy]

For reference, we used 3/16" drop with the AM pneumatic wheels. Zero issues with turning. Our setup was not standard tho. We had 8WD but performed more like a wide 6WD; our front wheels were raised 2" off the ground. So for us 3/16" was plenty.

[PayneTrain]

Originally Posted by Chris is me

That is largely because the 1/8" "standard" was settled on back when frame perimeters were 38x28. In 2014, most wheelbases were 28x28, so they may have been able to turn with very little or even no drop depending on the wheel choice and setup.

It was also when teams were running 4 inch or smaller high friction wheels. The 1/8 drop has been further standardized by the advent of the versablock, which when applied in a certain way in wcd configuration create a 1/8 drop.

We historically have tried to minimize the drop for better or worse. This year we were able to pull off 3/32 on the 8in AM pneumatic wheels.

[Jay O'Donnell]

Originally Posted by asid61

We tried 1/8" in 2014 and it was very noticeable. I've always thought that something between 1/16" ad 3/32" is a better drop for firm treaded wheels like blue nitrile.
What did people run in 2009, out of curiosity? Were drops even used?

As an unrelated side note, using omni wheels on the corners instead of treaded wheels will of course greatly reduce the required drop.

No need for a drop in 2009 because of the lower CoF, I think a lot of bots went with 4wd because of it. You see the same thing in battlebots too because of the steel floor.

[Chris is me]

Originally Posted by Jay O'Donnell

No need for a drop in 2009 because of the lower CoF, I think a lot of bots went with 4wd because of it.

While CoF was a factor, a much bigger factor was that nearly every competitive robot in 2009 already had a wheelbase wider than it was long, and didn't need a drop center to create this effect.

You can see this effect in games like 2012, teams who built wide robots did not need a drop center at all in order to turn.

[EricH]

Originally Posted by Chak

The concept is kind of correct. Still, I think what EricH was getting at was that 0.375" is not the absolute number due to other factors. For example, a drivetrain 48" long should have a different dropped distance compared to a drivetrain 20" long. A drop of .375" might not have the "upper hand" in both situations.

This is exactly what I was getting at.

@ ModMaster: I know the physics, at least in broad terms. You simply rehashed the broad physics without giving any numbers--even situational ones--to back up your assertion that "this dimension is the best". Just so you're aware, I was a student back when the WCD was introduced, in the area it was introduced in, and had the opportunity to learn about that drive, including the drop, from the teams that developed it.

If you're going to assert a blanket statement that "X is the best", this is a group of engineering types. You'll get an average of 1.33 counter-anecdotes per person on it not being optimal for a different configuration. (BTW, remember that 85% of statistics are made up on the spot--but in this post, it's 66%.)

[asid61]

Originally Posted by TheModMaster8

The reason you would want to do this is because it prevents the friction of a standard 4 wheeled pneumatic as well as, a 6 wheeled drive that has little to no wheel drop. The amount of centripetal force the robot experiences while turning either on a dime, or steering (like a car) causes the robot to stabilize on the center wheels, allowing it to turn easier... on the other hand, if wheel drop is too small, then the robot will not be able to achieve the same results because it doesn't have enough clearance to get on it's center wheels, this in turn causes more strain on the motors as well as the battery level. So basically what I am getting at is, that all wheel elevation/drops will work fine for their intended purposes, but 0.375" has the upper hand in terms of maneuverability as well as motor strain.

I believe Eric knows about the benefits of the dropped center wheel. What he's trying to say is that 3/8" may not always be correct, and making blanket statements is misleading.
Like I said, our practice bot ran 1/4" without issues for weeks. Factors like the length of the wheelbase, number of wheels, weight, and tire pressure are all things to be considered.