The afterthought bridge manipulator

[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?

[Teamcodeorange]

You can see our bridge manipulator in our robot demo video:

http://www.youtube.com/watch?v=Fpi9XnwSrpQ

Not to brag but it worked beautifully.

Team 399 and a few others in san diego also had competitive manipulators.

[philso]

We just finished assembling our replacement arm. It uses a van door motor driving an 8 inch diameter pulley to increase the torque and slow down the motion so that the limit switches have time to act. In the video, the limit switches are actually wired in series with the motor so that they cut off the power to the motor at the appropriate time. We used some 3mm Dyneema cord wrapped around the motor shaft and the pulley. We found some "non-traditional" material to make the body of the arm out of. It has more than adequate stiffness, was easy to work and has a low coefficient of friction.

http://www.youtube.com/watch?v=auKJTV7fTj4

We will see how well it works tomorrow at Lone Star.

[Akash Rastogi]

Originally Posted by 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.

^ This was our third iteration of a bridge arm and it worked okay.

V This is the design we had when we won the Mt. Olive MAR District event.

https://fbcdn-sphotos-a.akamaihd.net...9 69416_n.jpg

It is directly driven off a FP motor and gearbox with a coupling. The arm itself is welded tube. It is also our intake extension.

This is the bridge arm/drop down intake we will have attached to the same FP gearbox for the MAR Championship.

https://fbcdn-sphotos-a.akamaihd.net...547560 _n.jpg

https://fbcdn-sphotos-a.akamaihd.net...691814 _n.jpg

Worked out really well for us and I'm extremely proud of our rookie students for striving for continuous improvement.

[aldowyn]

We had this problem. Our arm was actually built in between competitions. The one we had at KC was a simple window-motor powered arm with a wheel on the end. It wasn't nearly strong enough, so we scrapped it.

Then we used two Fisher Price (I think Fisher Price...) motors (and those huge plastic gearboxes...), built an arm for each, and connected them with a bar. THAT worked.

[Sean Raia]

I want to thank everyone who contributed to this thread. Due to the suggestions given, we were able to construct a working bridge manipulator quite quickly.

Chief Delphi has come through for a team yet again!