Think about Robot Ground Clearance

[ggoldman]

I wanted to give a plea to all teams:

Please have some ground clearance on your robots.

With up to 60 points in the balance based on robots climbing onto one another, it would be a smart design choice to give your self some clearance underneath your frame so that you can climb onto other 'ramp' type robots during the endgame.

In terms of numbers:


In the picture attached to this post 'a' is the ground clearance of the frame and 'b' is the distance from the front of the frame to the point where the wheel makes contact with the ground. For simplication, we can assume that 'b' is 1/2 of the wheel diameter.

Therefore, with only a 1" ground clearance with 6" wheels, you can climb onto a ramp that is roughly 19 degrees in grade (use arctan{a/b}).

So just to reiterate, please consider sacrificing at least one inch of ground clearance to make you more of a team playing robot that can climb onto ramps a bit easier!

Gabriel Goldman
PhD Candidate
RoMeLa: Robotics and Mechanisms Laboratory
Virginia Tech http://www.me.vt.edu/romela

P.S. Feel free to contact me if you need any help with robot mechanisms (like cool four bar linkages!)

[Trample-Bot]

yes.....

if you have no possibility of lifting another robot... please, PLEASE, make sure you can climb at leats a 20 degree angle, or you willl just be a lump

[Andrew Blair]

Has anyone thought that instead of teams catering to ramp/lifter teams, ramp teams should be catering to the people being lifted?

Although, I agree that in any case, a little ground clearance is always a good idea.

[Trample-Bot]

Originally Posted by Andrew Blair

Has anyone thought that instead of teams catering to ramp/lifter teams, ramp teams should be catering to the people being lifted?

Although, I agree that in any case, a little ground clearance is always a good idea.

we are catering to the liftees, we are hoping to provide them with the lowest possible angle of inclination, but if their ground clearence is only 1/2", they are S.O.L.

[Ian S.]

This year will take alot of teamwork between alliances, so we should think of all the other teams at our regional(s) before designing our robots.

I also think that ramp/lift/crane bots can only do so much to help the bots being elevated have an easy time. If a teams robot can make it up a 20-25 degree angle ramp, and you have enough ground clearance, the team should be fine for the competition.

[AChastain]

A little clearance wouldn't hurt. There have been a lot of designs that drew a lot of criticism because the involved a ramp. Personally, I think if you going fast enough you can get up just about anything.

[T3_1565]

I agree. Clearance would be nice, not only for getting up ramps but also for those who arn't thinking of ramps at all but lifters... Someone thats only 1/2 inch thick will probably not be able to stand 120lbs being supposrted by it.

[MishraArtificer]

If all of the teams would build bots capable of getting onto last year's ramped platform, there'll be no problem.

[Ian Curtis]

Originally Posted by ggoldman

Therefore, with only a 1" ground clearance with 6" wheels, you can climb onto a ramp that is roughly 19 degrees in grade (use arctan{a/b}).

I'm confuzzled. I was just measuring our robot for last year, and it had 1/2 inch of ground clearance, and 4" wheels. It climbed the ramp extremely well with wedgetop tread. (Roughtop was different story altogether, becuase it wore out pretty much instantly spinning on lexan.) But we had six of them, does your math assume 4? (Your picture isn't showing up)

[eshteyn]

Originally Posted by Trample-Bot

we are catering to the liftees, we are hoping to provide them with the lowest possible angle of inclination, but if their ground clearence is only 1/2", they are S.O.L.

Your wrong on that, if the wheels are placed out to the outer extreme of the frame it's possible for them to climb. Also i would like to ask all teams, please, please have at least a minimum of .5 inches of clearance under your robot(including bumpers). More than .5 inches is preferable but at least .5 including bumpers.

[DanDon]

Originally Posted by eshteyn

Your wrong on that, if the wheels are placed out to the outer extreme of the frame it's possible for them to climb. Also i would like to ask all teams, please, please have at least a minimum of .5 inches of clearance under your robot(including bumpers). More than .5 inches is preferable but at least .5 including bumpers.

Wheels placed at the outer extremes of the frame might cuase their chassis to get caught on the lip of the ramp if they don't have enough ground clearance.

[Trample-Bot]

Originally Posted by AChastain

A little clearance wouldn't hurt. There have been a lot of designs that drew a lot of criticism because the involved a ramp. Personally, I think if you going fast enough you can get up just about anything.

you have to watch out though.... my mentor was talking about how our robot could potentially be damaged by other robots going a mile a minute in the heat of the competition...

[ggoldman]

iCurtis:


My math just assumed that the front bottom edge of the frame formed a right traingle with the ground and the point where the drive wheel makes contact with the ground.

From my experiance with FIRST, most teams do not place their wheels on the extremeties of their frames, so this is applying to teams who have wheels inside the footprint of their frames.


See the *crude* picture below:

....................FRAME
.....------------------------------------
.....l......*.................*
..a l.......*.....WHEEL..*
.....l.........*............*
.....l<------> ****.............------->x
..........b

a = distance from edge of frame to ground
b= distance (in the x direction) from edge of frame to contact point wheel makes with ground (assumed to be the radius of the wheel).

Hopefully this clears it up a bit!