pic: Effective Aperture of Low Bar Defense

[bt20304]

hey, looking at measurements in solidworks, you seem to be off.
in reality the field elements are 13.73" measured the same way
https://drive.google.com/open?id=0B4...G5rM1Q0YlNCYmc

[pHolmgren]

Thanks for this! It really helped us visualize what's needed for a low bar robot.

[Madison]

Originally Posted by bt20304

hey, looking at measurements in solidworks, you seem to be off.
in reality the field elements are 13.73" measured the same way
https://drive.google.com/open?id=0B4...G5rM1Q0YlNCYmc

When I measure against the field model provided by Autodesk, I get 13.86". Did you model those elements yourself or were they taken from elsewhere?

In any case, that discrepancy is why I added a disclaimer in this thread saying that y'all shouldn't take my word for it and should check things out yourselves.

[Kevin Sevcik]

Originally Posted by Nebster

I was thinking about this too. Something where the front end of the robot is less than the ~14" limit for when the robot is on the ramp, but the rest of the robot can go up to 15.9" or so and be fine.

Warning- MS Paint incoming:

Those slopes would go a lot farther back, depending on how long the robot is and where the CG is. The initial approach would actually have a better aperture, since you're on your front wheels and rear wheels, and thus at a shallower angle. Then the aperture would shrink down to whatever that minimum amount is, until your CG (or something else) tilts you down to horizontal again.

Coming from the backside is even worse. If you're not flat before you get to that bar, you're going to have to be something like 3" shorter yet. so that end of your robot will have to be 11" or maybe even 10".

The real answer to all this, of course, is to make up an inventor sketch of a side view of the low bar and your chassis and layout. And then run your chassis through with wheels tangent to the correct surfaces, and see what happens.

[PayneTrain]

Thanks for posting this. This was a fact some teams were able to catch very early, but unfortunately we all know we are going to get to events and see a 15.9" tall robot with a strategy designed around a nontrivial utilization of the low bar.

[pHolmgren]

I know it must be do-able but the challenge is fitting a firing mechanism in that space, to shoot in the high goal.

[EricLeifermann]

Unless your drive base is the exact length of the defense ramps your robot isn't going to be on a 13.5 degree angle.

I suggest all teams put in their robot in a sketch and run it through like it was actually driving through the low bar. The height of that bar isn't as low as people are making it out to be if your drive is designed correctly.

[pfreivald]

I realized this problem right away, but appear to have gotten the orientation of the low bar backward--I thought the bar was closer to the Courtyard, rather than to the Neutral Zone. Thanks, Madison!

[mplanchard]

All the Field models were provided by FIRST and imported into SOLIDWORKS.

AndyMark and VEX Robotics models were designed originally in SOLIDWORKS and provided by these manufactures directly to us to create our KOP.

Industrial suppliers such as SMC BIMBA FESTO also have validated models on 3DContentCentral.

You should always verify models. Good engineering practice. Marie.

[Kevin Sevcik]

Originally Posted by EricLeifermann

Unless your drive base is the exact length of the defense ramps your robot isn't going to be on a 13.5 degree angle.

I suggest all teams put in their robot in a sketch and run it through like it was actually driving through the low bar. The height of that bar isn't as low as people are making it out to be if your drive is designed correctly.

This depends somewhat on your CoM. If you have a CoM near the back, you might not fall down horizontal until you're well into the low bar. At which point you'd start pushing against the low bar. Just CAD isn't going to give you those details.

[dsergison]

it's worth drawing up for your own wheelbase... 6 or 8 wheel bots likely have 24-36" wheelbases, so they never sit on the ramp at the ramp angle, so their effective aperture is not quite as bad as shown....

also, the aperture isn't symmetrical.

It's a weird obstacle for sure. It will be interesting to see how people hang up on it. It has a lot of potential to completely jam some bots for the duration.