The afterthought bridge manipulator

[Sean Raia]

After our first regional this year, our team has learned a lot about this game.
One thing we (and quite a few other teams) didn't see coming was the difficulty of lowering those bridges.
Our bridge arm was the last system to be designed, and was not given enough weight/space allotment. For that reason, we ended up having a "you lower it and we'l follow you up there" robot. We tried at least two different designs both powered by a window motor, to no avail. Then again, with 5 pounds of weight to spare for a manipulator, what can you expect?

I'm curious as to who else was in this boat, and if they found a way to overcome this problem. It would be interesting to discuss last ditch bridge manipulator implementations, and their effectiveness.

[Koko Ed]

Every year there is always an aspect of the game that people underestimate that in the end cost them the opportunity to win the game. The ability to negotiate the bumps and manipulate the bridges is this year's bugaboo. I have seen plenty of robots helplessly paw at the bridge for the endgame and I have seen robots get stopped cold at the bump as if they hit a brick wall. I think teams figured scoring balls were more important and while it can make you dominant the ability to consistently make it on the bridge (especially the Coopertition Bridge during Qualification matches) is practically invaluable.

[Mk.32]

We were in the same boat, and it hurt.. a lot...

For off season I am thinking of just strapping a 1.5inch bore Pneumatic cylinder on the side of the robot and using that to push the bridge down.

[Sean Raia]

Originally Posted by Mk.32

We were in the same boat, and it hurt.. a lot...

For off season I am thinking of just strapping a 1.5inch bore Pneumatic cylinder on the side of the robot and using that to push the bridge down.

We had this same idea, we do not run a compressor on the robot though so this would be tough, UNLESS we charged our air before each match and never charged it on the field
Plausible?

I agree that bridge manipulation is invaluable, it's unfortunate that many of us cannot yet do it.

[Mk.32]

From our last year experiences, think 2inch bore x 24 inch cylinder, we found it best to run a compressor on board for anything bigger then .75inches; your mileage may differ.
The biggest problem without running a compressor is tiny leaks, we per-charged this year and then by the time we got onto the field we found we lost already 15PSI.

[akoscielski3]

We had the same problem in Smoky Mountains. Our bridge manipulator turned out to be the worst part of our robot. We tried to fix it but it eventually became this

So after the regional I started designing. I had 10 pounds to work with, 5 from the old one and then we sacrificed the angle changer on our shooter and will change the speed instead, which gave another 5 ish pounds.

This is what i designed
Down
Up

Current weight is about 6 pounds. We dont have to add any electronics because the old electronics are still there.

Though for us depending on another robot for a bridge manipulator worked! We are undefeated right now, and won Smoky Mountains.

[Sean Raia]

Originally Posted by akoscielski3

We had the same problem in Smoky Mountains. Our bridge manipulator turned out to be the worst part of our robot. We tried to fix it but it eventually became this

So after the regional I started designing. I had 10 pounds to work with, 5 from the old one and then we sacrificed the angle changer on our shooter and will change the speed instead, which gave another 5 ish pounds.

This is what i designed
Down
Up

Current weight is about 6 pounds. We dont have to add any electronics because the old electronics are still there.

Though for us depending on another robot for a bridge manipulator worked! We are undefeated right now, and won Smoky Mountains.

Nice design! Are you running a window motor to power that?

[akoscielski3]

Originally Posted by Sean Raia

Nice design! Are you running a window motor to power that?

NO! lol sorry PLEASE DO NO USE A WINDOW MOTOR!!!!!!!!!! Im putting on a fisher price motor. The gearbox is there in the picture The old Bridge manipulator was a window motor, but it doesnt have nearly enough torque to push the bridge down.

[Travis Hoffman]

Originally Posted by akoscielski3

Though for us depending on another robot for a bridge manipulator worked! We are undefeated right now, and won Smoky Mountains.

Word.

But we shouldn't have this dependency in Wisconsin.

[akoscielski3]

We will definitely need a bridge manipulator if we want to be competitive against 1114, 2056 and 188 in GTR West.

[daniel_dsouza]

We haven't attended a regional yet (we are week four), but we have spent enough time going up/down bridges with our robot to comment here...

Our team prototyped a bridge manipulator that would push the bridge down, and like some of the other posters figured out that using an arm to do all the pushing was not as simple as some thought. The moment we thought we should change designs was when our robot ran over our bridge manipulator...

In the end, we created an mechanism that acts as a ramp, and uses the power of our drivetrain to lower the bridge. When approaching the bridge, the driver will lower the mechanism out over our bumpers, and hit the bridge. The lip of the bridge will slide down the ramp (like so: -evil bridge lip-\[robot here]). When the bridge's lip reaches the bottom the the ramp, the wheels will be able to roll onto the bridge.

[ksafin]

The problem a lot of teams had was the approach.

Many teams used the approach of ramming the bridge with an angle to bring it down.
Although this works fine with a lightweight easily-turnable bridge that most of us built, it won't work with the real bridge.

The reason being, of the torque you had when you rammed the bridge, only a fraction of it is actually used because you're not applying a direct vertical linear push.

Like someone said, having a 2" bore 12" stroke cylinder will do wonders; if you push vertically on the bridge from above, it'll have no issue pushing it down (consider 60 psi with 2" bore - lots of force!).

[Akash Rastogi]

By the end of our event, we had modified our bridge arm to use a wedge that worked well, should have used that design from the start. If you have a van door motor, use that.

[rcmolloy]

If any teams are thinking of revising their bridge manipulator, I would highly suggest looking at 67's intake, bridge manipulator, stinger combo. After viewing the awesome structure flawlessly pull down the co-op bridge in auto and balance 3 robots in elims, I think there would be a great benefit if a team could mimic what HOT has produced.

[quinxorin]

Originally Posted by ksafin

The problem a lot of teams had was the approach.

Many teams used the approach of ramming the bridge with an angle to bring it down.
Although this works fine with a lightweight easily-turnable bridge that most of us built, it won't work with the real bridge.

The reason being, of the torque you had when you rammed the bridge, only a fraction of it is actually used because you're not applying a direct vertical linear push.

We use the wedge approach, but we made sure it worked right by making sure we built our bridge right. It takes 17.1lbs of force to push an official bridge down at the ends, and on one end of our practice bridge it takes exactly that amount of force. (On the other, it takes a little more, just so we could make sure our wedge performed better than it had to). The wedge begins at 37deg above horizontal at the uppermost end, but is slightly concave, so it ends at 39.75deg above horizontal. It extends 13 7/8 from the frame of the robot, is 12 1/2 inches off the ground, and when the bridge is pushed down it clears the bumpers by about half a millimeter. Very close tolerances! It has some slippery plastic (delrin) covering the sliding surface, so there is very little friction. The wedge is pneumatically driven with two 1 1/16, 10" stroke cylinders.

Want to see it work?