Bumbers and Trailor Hitch

[sxysweed]

Been through the search here and on Google, but can't find it. A teammate of mine mention he saw something on here where someone calculated how big of a space you need between the bumbers and the trailor hitch to still comply with the rules...

Anyone care to help us?
Thanks.

[MrForbes]

Measure your bumper perimeter. You need to cover at least 2/3 of that with bumpers.

[EricH]

squirrel, the question is not how much space you need to cover. The question is how much space can you have between your trailer hitch and your bumpers. There is a difference...

My standard answer (this has been answered several times) is that it depends on your robot. I think I offered to do the trig when I got time, but I haven't had that time yet. Maybe later today...

[sxysweed]

Originally Posted by squirrel

Measure your bumper perimeter. You need to cover at least 2/3 of that with bumpers.

Not that part, but the whole the bumpers on the trailors have the collide with bumpers on the robot before the hitch colides with the bumpers. As in, did someone find the magic number?

[Rick Wagner]

We have 4.5 inches on each side of the trailer hitch, with six inch bumpers on the rear, and it has plenty of clearance, according to our CAD model.

[MrForbes]

I think what I said still applies...if you cover 2/3 of your bumper perimeter with bumpers, and leave the excess space on either side of the trailer hitch, you should be fine.

Or am I missing something?

[EricH]

Originally Posted by squirrel

I think what I said still applies...if you cover 2/3 of your bumper perimeter with bumpers, and leave the excess space on either side of the trailer hitch, you should be fine.

Or am I missing something?

Yeah, but your response doesn't fully answer the question asked.

Here's the more full answer: The maximum distance between the bumpers and the trailer hitch is 1 side of your robot, minus 12" for bumpers, minus 7" for the hitch. Assuming that you have the hitch centered, divide by 2.

You also probably don't want to have the bumpers right next to the hitch (zero distance), because the trailer tongue will hit first. You have to have the bumpers hit first. I'm not sure about the trailer distances, especially to the bumper edges, or I'd do some trig for a standard 28" and 36" robot.

[sxysweed]

Originally Posted by EricH

Yeah, but your response doesn't fully answer the question asked.

Here's the more full answer: The maximum distance between the bumpers and the trailer hitch is 1 side of your robot, minus 12" for bumpers, minus 7" for the hitch. Assuming that you have the hitch centered, divide by 2.

You also probably don't want to have the bumpers right next to the hitch (zero distance), because the trailer tongue will hit first. You have to have the bumpers hit first. I'm not sure about the trailer distances, especially to the bumper edges, or I'd do some trig for a standard 28" and 36" robot.

I'm kinda lost. I'm also sleep/food deprived...

We can't download the PDF for the rules and stuff (restricted access rights on the computer), but how long is the trailor hitch tongue?

If you care to work it out, our robot's backside (mounting end) is 37" long....

[Alan Anderson]

Originally Posted by sxysweed

We can't download the PDF for the rules and stuff (restricted access rights on the computer),..

Someone on your team has them, right? And they are available to all the team members, right?

[dtengineering]

Perhaps what Jim is getting at is that the spacing at the back is actually largely pre-determined by other bumper rule requirements.

Consider that for a typical 27x37 rectangular robot, you have a perimeter of 128". That means you require 85.3" of bumpers as a minimum in order to cover 2/3 of the perimeter.

If you have the maximum width opening on the front of your robot, you will still have 12" of bumpers (two 6" sections) on the front of the robot.

For a robot in the wide configuration, assuming full bumpers along each side, that adds another 54" of bumpers, bringing the total length of bumpers on the front and sides to 66". That means you are required to have a minimum of two 10" long bumpers on the rear of the robot. These minimum lengths do meet the trailer hitch requirement.

For a robot in the long configuration, assuming full bumpers along each side, you will have 74" of bumpers along the sides. This means that you will have essentially met the 2/3 requirement and will only have to put the minimum 6" long bumper segments on the back. This, too, should meet the trailer hitch requirements, or else the GDC would have effectively outlawed long configuration rectangular robots with front openings.

You will note that I use a 27x37" robot... you have to be braver than I to get too much closer to the maximum 28x38" limits. It is nice to not have to worry about size and weight when clearing tech.

If you are clever enough to have come up with a custom frame of non-rectangular shape, or have some weird opening on the side of the robot for some purpose, then, of course, these calculations are not immediately relevant to your situation.


Jason

[EricH]

Originally Posted by sxysweed

I'm kinda lost. I'm also sleep/food deprived...

We can't download the PDF for the rules and stuff (restricted access rights on the computer), but how long is the trailor hitch tongue?

If you care to work it out, our robot's backside (mounting end) is 37" long....

It's not the back end of the robot I don't know, it's the short side of a right triangle. And the real length of the long side. The best that I could come up with is that if the bumpers are right against the hitch, you get a maximum swing of 120*, which probably isn't enough for most robots. (60* each side from straight out.)