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-   -   6 wheel drop center drive train (http://www.chiefdelphi.com/forums/showthread.php?t=149108)

Chris is me 24-06-2016 15:51
Re: 6 wheel drop center drive train
 
Quote:
Originally Posted by asid61 (Post 1594200)
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.
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.

bigbeezy 24-06-2016 16:01
Re: 6 wheel drop center drive train
 
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.

Jay O'Donnell 24-06-2016 16:02
Re: 6 wheel drop center drive train
 
Quote:
Originally Posted by asid61 (Post 1594200)
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 24-06-2016 16:28
Re: 6 wheel drop center drive train
 
Quote:
Originally Posted by Jay O'Donnell (Post 1594204)
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.

PayneTrain 24-06-2016 17:04
Re: 6 wheel drop center drive train
 
Quote:
Originally Posted by Chris is me (Post 1594201)
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.

EricH 24-06-2016 20:28
Re: 6 wheel drop center drive train
 
Quote:
Originally Posted by Chak (Post 1594197)
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%.)


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