Minimum Ground Clearance?
 

Hello everybody,

I am currently designing our WCD drive train, hopefully using AndyMark's Performance Wheel. Since we have never used 4" wheels before, ground clearance has never been a problem. How much ground clearance should there be between the floor and the bottom of the robot ur gearbox is about .2 inches off the floor as of now)

Also, if this ground clearance needs to be increased, what would be some methods of raising the gearbox from the floor.

Re: Minimum Ground Clearance?
 

Our 2009 robot had 1/8" of clearance from the floor to the sideplate flanges on our non-WCD drivetrain.

So, the short answer would be "depends on the game"

Re: Minimum Ground Clearance?
 

I think that 0.25" to 0.375" (3/8) ground clearance is ideal. That said, I have never built a WCD. Additionally, every game is different. For Breakaway, one might choose up to 1" of ground clearance, whereas for LogoMotion, 0.25" is more than enough. As to your second question, I believe you infer lowering the gearbox as opposed to raising it. Nonetheless, you can machine profiles out of, say, .25" 6061 designed after the mounted face of the gearbox.
Also, if you'd shoot me your CAD, I could take a look at it and provide some help with the frame design. I would love to do so. Based on the screenshot, I assume you are using SW?
Good Luck!

Re: Minimum Ground Clearance?
 

our robot was 3/32 off the ground this year (1/8 off the ground + rivet heads). I would say that that is the ABSOLUTE limit to how low you can make a robot. while it ran well on the field, it high centered on nearly every thing at our school:

Seams in concrete floors, (underneath carpet)
doorways
a zip tie

I advise more than .5 inches, and check the nominal diameter. the andymark wheels are usualy .05-.15 smaller than what they are marketed as. (quickly removing the .375 inches of ground clearance we had)

Re: Minimum Ground Clearance?
 

A lot of field objects are attached to 3/4" plywood. If you can't clear the plywood, you could seriously limit your playing field or, worse, get hung up. Review old playing field drawings. Other than that, the inspection sheet has a suggested 1" minimum, but there hasn't been a formal design constraint in my tenure.

Re: Minimum Ground Clearance?
 

Adam.
You don't know what the game will be so designing for ground clearance now is premature.

Re: Minimum Ground Clearance?
 

Just because FIRST says the field is flat, does not mean the field is flat. Regardless of game, I would be hesitant to recommend anything less than 1/2" of clearance (and I would feel safer up around 3/4").

Re: Minimum Ground Clearance?
 

Seconding this recommendation. IF the field claims it is flat there is a fairly good chance that there will be some flex in the floor under the field. This also why omni directional drive systems need some sort of suspension to keep all the wheels touching.

Re: Minimum Ground Clearance?
 

95 typically aims for 3/4in-1in. It's a comfortable margin on carpet thickness, and very close on that 3/4in plywood. Go conservatively high if you use a skyway type, or similar, wheel where the wheel tread wears down appreciably.

The robot is not a track car (duh? ;) ) so there usually isn't much advantage to a very low ground clearance in my experience.

Re: Minimum Ground Clearance?
 

We ran as low as half an inch last year without issue. We could drive and turn anywhere and never got hung up. Just because your ground clearance is less than a bump doesn't mean you'll get hung up on it. Lots of teams had less than 12 inches of ground clearance in 2010 :)

On a "flat" field, I would recommend a half inch minimum. On a field with any obstacle, I'd probably recommend raising that up a notch or two. If next year's game has obstacles, we'll probably just throw bigger wheels onto our drivetrain to make it easy.

Re: Minimum Ground Clearance?
 

Once upon a time I made the decision to shoot for ~1/8" ground clearance. This was for Overdrive. Little did I know that the field would have raised bumps holding up the center divider. While it didn't cause a massive issue, it was something we needed to monitor throughout the season.

I would recommend at the minimum 3/8", with somewhere between 1/2"-3/4" to be ideal.

-Brando

Re: Minimum Ground Clearance?
 

Just to throw a wrench in this discussion. Years like 2005 saw teams get hung up on tetras due to either having too much or too little ground clearance. Also, in games like 2003 you had to worry about wheel width.

Re: Minimum Ground Clearance?
 

That's why 330 put blocks on the very front of their frame on the bottom--high ground clearance, comparatively (say, about 2-2.5 inches where the blocks weren't), but I don't remember that we ever got hung up on a tetra. (It also provided a good place to mount our loading-zone feelers.) The blocks were designed with an angled back so we could escape from a tetra if it did get under us.