Ground Clearance Vex clamping gearbox

[steelerborn]

So we attended the SCRRF Scrimmage on Saturday, and we found out while we were there that we needed to raise our frame by at least an inch.

Originally we wanted to keep a low cg with a low ground clearance in order to lift stacks with no fear of tipping. Driving over the scoring zones was not something we wanted to pursue. In our first match driving on the field for the first time we clipped the corner of a scoring zone and damaged the hardboard (not hdpe which the actual field would have). Talking to the field crew and inspectors they mentioned that if they saw a bot with very little ground clearance, changes would need to be made since they will not pass inspection.
Originally it didn't seem like they wanted us to continue to practice until we fixed it, but at the time we did not have the correct tools to fix the problem at the event. Thankfully the staff was understanding and allowed us to continue to practice and even gave us some great ideas as to how to fix it. Unfortunately being so close to bag and tag we could not pursue the other options.

We did however come up with a great solution. We are running the vexpro clamping gearbox so all we had to do was cut some 3"x1" tubing in 2" sections. We then attached the gearbox and drilled the necessary holes and bolted it to the frame. It raised our entire robot by 3 inches. Thankfully our intake system still works at the new height, only slight changes needed to be made to the elevator, and we are now able to drive over the scoring zones even with 4 inch mecanum wheels. All of the changes were able to be done in about 3-4 hours.

The main incentive for this post is to let everyone know about the ground clearance issue and passing inspection, and also to propose a solution for teams that are using the vex pro clamping gearbox.

https://onedrive.live.com/redir?resid=CEBED2B660E90E05!14018&authkey=!ADkXvK zqNzDq-fU&v=3&ithint=photo%2cjpg

[Kevin Sevcik]

That still looks pretty exciting for my tastes. We CADed up a long chassis with 6" wheels and the clamping gearboxes and realized things would be awfully tight since our gearboxes are fairly centrally located. If we crossed the scoring platform square, we'd still have the gearbox gear scraping the platform for a bit. Someone suggested we just toss a hex bore wheel on the outside of the gear, but when I noted that we'd still high center badly if we strafed sideways into the corner, we switched to 8" wheels instead. That decision seems to have been trading one clearance issue for another, however...

[Lil' Lavery]

What rule were these inspectors citing claiming they would fail you for a low ground clearance? So long as all your leading edges meet R7, I don't see any reason for a low ground clearance to cause an inspection failure.

[AdamHeard]

Originally Posted by Lil' Lavery

What rule were these inspectors citing claiming they would fail you for a low ground clearance? So long as all your leading edges meet R7, I don't see any reason for a low ground clearance to cause an inspection failure.

Overzealous interpretation of R16G? I don't think the actual HDPE platforms will get too damaged though.

[Lil' Lavery]

Originally Posted by AdamHeard

Overzealous interpretation of R16G? I don't think the actual HDPE platforms will get too damaged though.

R16 is about lubricants
The nearest rule I can find with part G is R15G, which is about displaying your robot outside of the bag.
Not sure which rule you're referencing.

[AdamHeard]

Originally Posted by Lil' Lavery

R16 is about lubricants
The nearest rule I can find with part G is R15G, which is about displaying your robot outside of the bag.
Not sure which rule you're referencing.

Ooops. G16G. Thanks.

[Chris is me]

There is no rule or inspection requirement that demands your robot be able to clear the bumps. That would be ridiculous.

That said, this is a clever solution, and thanks for sharing. Rectangular tubing of all shapes and sizes (not just 1x1 and 2x1) can be quite useful in FRC. I'm a fan of 3x1.5 for internal belt runs, 1.5x1 for live axle manipulators that you press bearings directly into, and other random sizes for anything from gearboxes to framing.

[EricH]

Originally Posted by Chris is me

There is no rule or inspection requirement that demands your robot be able to clear the bumps. That would be ridiculous.

Correct. However, as noted, G16G requires robots not to damage the field--and gives the appropriate parties the authority to require robots that do to go get fixed. There are some teams that will note that an otherwise-legal robot damaged the field, and the Head Referee sent them back to the LRI with a message of "Fix This". It happens.

If you can't go over the scoring platforms, that is a design choice you made. If you damage them in an attempt to go over them, that is a rules problem... which can be fixed either by you not attempting to go over the platforms or by fixing the robot.

[Gregor]

Originally Posted by EricH

Correct. However, as noted, G16G requires robots not to damage the field--and gives the appropriate parties the authority to require robots that do to go get fixed. There are some teams that will note that an otherwise-legal robot damaged the field, and the Head Referee sent them back to the LRI with a message of "Fix This". It happens.

If you can't go over the scoring platforms, that is a design choice you made. If you damage them in an attempt to go over them, that is a rules problem... which can be fixed either by you not attempting to go over the platforms or by fixing the robot.

Have you seen a correctly covered scoring platform? If a team manages to damage it I'll give them the creativity award.

[EricH]

Originally Posted by Gregor

Have you seen a correctly covered scoring platform? If a team manages to damage it I'll give them the creativity award.

Not yet.


OTOH, HDPE has been used on field elements before (before your time, I think--03, 04, 06), and had a tendency to get a bit scratched up. Not too bad... but enough to be noticeable.

[Gregor]

Originally Posted by EricH

Not yet.


OTOH, HDPE has been used on field elements before (before your time, I think--03, 04, 06), and had a tendency to get a bit scratched up. Not too bad... but enough to be noticeable.

As a ref I wouldn't ever foul a team for scratching plastic on the ground. Would you?

[Kevin Sevcik]

Originally Posted by Gregor

Have you seen a correctly covered scoring platform? If a team manages to damage it I'll give them the creativity award.

I believe I mentioned our robot was all set to high center on the large gear of a clamping gearbox. I think a gear spinning at 900rpm with 50lbs of down force might be bad for the hdpe. Nevermind if said gear hits one of the seams.

[steelerborn]

We only damaged the field in the very first practice match, after that we never hit the platform again and we played probably 17 matches.

But we were told that since our ground clearance was so low that we "could" damage the scoring zones so our frame would not pass inspection. I felt this was odd because you are flagging a robot for what "could" happen in the field, but if the intent was to damage the field I am sure teams could find a way and we would have many more robots not pass inspection.

For teams with low clearance just avoid the zones but probably start brainstorming options to raise your frame just in case.

[steelerborn]

I agree with you Adam the hdpe should be fine. But we figured better be safe than sorry and made the changes.

[steelerborn]

Increasing the wheel diameter was an option we were looking at that as well, but it is just too expensive. Our 4 inch wheels seem to work fine as long as we just go right over the platform (no strafing while on the platform). And we no longer can "knick" the ends of the platform, which is what happened at the practice event.