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]

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 :eek:
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.

[Kim Masi]

I watched a lot of teams (both veterans and rookies) struggle with this over the weekend. I'm not sure if the issue was more geometry or providing enough torque to the bridge to lower it.

One of the most clever methods I've seen is team 103, who has two curved pieces of tubing that flip down and so when they drive up to the bridge the natural motion of their forward momentum causes the bridge to tilt and allowed for them to get up pretty easily. It was a pretty effective, light weight and passive way of lowering the ramp without having to stop and wait for some other mechanism to push the bridge down. If I can find a pic I'll post it.

Or you could try the 25 method: bump the bridge, pop a wheelie and then get on. Seemed to work well for them :rolleyes:

[SenorZ]

Our regional is next week. After watching weeks 1 & 2 we're scrambling to make a bridge manipulator:
Andymark gearmotor (KOP) on a length of c-channel with a small wheel on the end.
This is untested and will not get a chance until Thursday.
Fingers crossed!

[Andrew Lawrence]

Our regional is next week. After watching weeks 1 & 2 we're scrambling to make a bridge manipulator:
Andymark gearmotor (KOP) on a length of c-channel with a small wheel on the end.
This is untested and will not get a chance until Thursday.
Fingers crossed!

Gear that down. A LOT. Make it go slower than molasses with gearing. You'll need he torque

[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 (https://plus.google.com/photos/102078272419093677000/albums/5652326859077900449/5718702712242418002?hl=en)

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 (https://plus.google.com/photos/102078272419093677000/albums/5652326859077900449/5718705377946268514?hl=en)
Up (https://plus.google.com/photos/102078272419093677000/albums/5652326859077900449/5718705613659087714?hl=en)

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. :D

[Sean Raia]

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 (https://plus.google.com/photos/102078272419093677000/albums/5652326859077900449/5718702712242418002?hl=en)

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 (https://plus.google.com/photos/102078272419093677000/albums/5652326859077900449/5718705377946268514?hl=en)
Up (https://plus.google.com/photos/102078272419093677000/albums/5652326859077900449/5718705613659087714?hl=en)

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. :D

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

[akoscielski3]

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 :P The old Bridge manipulator was a window motor, but it doesnt have nearly enough torque to push the bridge down.

[Travis Hoffman]

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

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.

[DominickC]

We had originally designed our cannon to have a barrel extension which extended the length of the cannon when in the firing position, but realized the cannon was just barely long enough to get the bridge down. During build week 5, we reversed the extender to extend the cannon when it was in the down position, making it very easy to put the bridge down.

[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.

[Agentarrow]

One of the big reasons that teams have such trouble lowering the bridge is that many assumed that bridge dynamics of the plywood version would be the same as the real bridge and paid dearly for this oversight. Even a weighted plywood bridge that passes the "battery test" for comp-type dynamics is really different from the actual bridge at the events. Take the time before any future events to prep an overpowered bridge tipper.

[BrendanB]

Our regional is next week. After watching weeks 1 & 2 we're scrambling to make a bridge manipulator:
Andymark gearmotor (KOP) on a length of c-channel with a small wheel on the end.
This is untested and will not get a chance until Thursday.
Fingers crossed!

We are using the gearmotor to lower our ball pickup/bridge manipulator with a 2 to 1 ratio and we sometimes need to get the bridge rocking to get it down. I'd recommend a 3 to 1 ratio and you'll get that sucker down no problem.

A simple solution I saw at GSR was 1519's. It is a simple triangle driven by a window motor that comes down and they just drive into the bridge and it comes down. Can easily be down with a limited weight budget! You can see it on the side of there robot here! (http://www.chiefdelphi.com/media/photos/37597)

[quinxorin]

At the beginning of the season, we created a list of priorities for game tasks. We determined that, since the coopertition bridge was just as important as winning, manipulating the bridge was our second priority (first priority went to moving the robot). This allowed us to put a lot of thought into making a simple, elegant manipulator that was finished by the end of week 3. And entirely student-designed and built too!

Here's some links:
3D Model of robot (no special software required) (http://freewheel.autodesk.com/dwf_s.aspx?dwf=http://www.lightningrobotics.com/Contents/Uploads/cad_uploads/eddie.dwf)
Robot technical description (http://lightningrobotics.com/Contents/index.php?pagename=eddie)
Video of bridge manipulator (we're 862, the robot farthest from the camera at the start) (http://www.youtube.com/watch?v=PFiLn3HW2FE&feature=youtu.be)

[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]

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? (http://www.youtube.com/watch?v=PFiLn3HW2FE&feature=youtu.be)

[Sean Raia]

We are using the gearmotor to lower our ball pickup/bridge manipulator with a 2 to 1 ratio and we sometimes need to get the bridge rocking to get it down. I'd recommend a 3 to 1 ratio and you'll get that sucker down no problem.

A simple solution I saw at GSR was 1519's. It is a simple triangle driven by a window motor that comes down and they just drive into the bridge and it comes down. Can easily be down with a limited weight budget! You can see it on the side of there robot here! (http://www.chiefdelphi.com/media/photos/37597)

This design interests me, I wish I could get a better pic of that manipulator. I'l go hunting...

@Akash, You mentioned using a van door motor. Does that have enough torque to push the bridge down on its own, or is it better off being used for a wedge?

[Sb28000]

With the help of 2614 (M.A.R.S. - Thanks again, and congrats on the Regional win!), we built a bridge lowerer on Friday in Pittsburgh - we mounted a van door motor to a length of aluminum angle, and screwed that into a wooden upright already on our robot. We then sandwiched a bar of 80-20 with a 6" KOP wheel on the end of it on one side of the flat part of the shaft, with another piece of aluminum angle on the other side of the motor output shaft. Although functional, beware of the extreme torque and force that pushing down the bridge can cause, and the damage it can do to your 'bot. During a qualification match, we found that our arm did not have enough force to push down the bridge. Having tested it just minutes before that match, we were puzzled until we saw that a nut that had been sitting flush on the 80-20 bar was now pushed into the bar, with the top surface of the nut even with the surface of the bar. One of two bolts holding the whole thing together had now shifted and was not holding tension against the motor shaft. We swapped it out Saturday morning for steel on the surfaces touching the output shaft.

[dsalvucci]

To build on what Dom had posted on regards to the cannon. Team 23 had built a plywood bridge and then put 10 lbs on the opposite side of the bridge for testing so that we knew our air cannon design could push it down. We originally had belts driving the cannon up and down via window motor power, but quickly realized it was not strong enough and switched to a timing belt idea (black plastic belt with teeth on one side).

Opposed to the OP's title, however. Team 23 quickly recognized that the importance of the bridge was way more than shooting and focused largely on a design that could do everything asked. ie the cannon was a ball pickup, shooter, and bridge manipulator

[Brandon_L]

If I saw this thread earlier, I would have posted it as a reply here. Sorry that I missed it. We had the same problem, and this is how we fixed it. (http://www.chiefdelphi.com/forums/showthread.php?t=104469)

[commodoredl]

Our team, while designing our bridge manipulator, wanted it to be as simple and intuitive to use as possible. We knew that an arm could have multiple uses, but would also need a driver to judge distances to work properly. Instead, we built a wedge that allows the driver to drive straight into the bridge and lower it.
Here's a picture of the wedge in its down position:
https://fbcdn-sphotos-a.akamaihd.net/hphotos-ak-snc7/418280_387297064614621_196698817007781_1560770_168 0531978_n.jpg
It's not perfect. The wedge had to be fit into a very small section of our robot, and because of that it unfolds a little awkwardly sometimes in autonomous (but our human operation doesn't have a problem with it). We also ran into an issue where even though the wedge was supposed to be supported by our bumpers, it still rode up when hitting the bridge (actually pushing back into our main breaker in a practice match and shutting us off).
The solution we came up with to transfer maximum force and reduce the backdriving was a simple bar of angle iron stretching across the wedge near the bottom part of it. This pushes straight into the bumpers and keeps it a tight fit as the robot lowers the bridge.
Altogether it probably weighs 5-10 pounds and uses one window motor. I don't have the exact weight now since we added parts to the subsystem in the competition. But it allowed us to lower the bridge perfectly all weekend.

[mathking]

We built our first prototype with a window motor. Worked great until we weighted the bridge. Then we went to the gear motor. Better but still the same result. So we did a 3.5 to 1 reduction (via chain) and it seems to work now. There is a roller made of delrin on the end to allow it to roll on the ramp surface as we drive forward. We have not been to a regional to test it yet, but since our manipulator will lift the front of the robot off the ground, if it does not push down the bridge making it stronger won't help.

We too waited longer than I would like to get a working prototype, but we did plan for how and where to mount it. We are using a couple of pieces of 1x2 tubing (with slotting to reduce weight). One as a the arm and one as a mount for the arm and motor. One thing we did decide on early was that our design should be able to both push down and push up the bridge.

In any event, the whole assembly weighs about 4.8 pounds, and is one unit. So it just takes four bolts and quick connecting the wires to mount it.

[Brandon_L]

Our team, while designing our bridge manipulator, wanted it to be as simple and intuitive to use as possible. We knew that an arm could have multiple uses, but would also need a driver to judge distances to work properly. Instead, we built a wedge that allows the driver to drive straight into the bridge and lower it.
Here's a picture of the wedge in its down position:
https://fbcdn-sphotos-a.akamaihd.net/hphotos-ak-snc7/418280_387297064614621_196698817007781_1560770_168 0531978_n.jpg
It's not perfect. The wedge had to be fit into a very small section of our robot, and because of that it unfolds a little awkwardly sometimes in autonomous (but our human operation doesn't have a problem with it). We also ran into an issue where even though the wedge was supposed to be supported by our bumpers, it still rode up when hitting the bridge (actually pushing back into our main breaker in a practice match and shutting us off).
The solution we came up with to transfer maximum force and reduce the backdriving was a simple bar of angle iron stretching across the wedge near the bottom part of it. This pushes straight into the bumpers and keeps it a tight fit as the robot lowers the bridge.
Altogether it probably weighs 5-10 pounds and uses one window motor. I don't have the exact weight now since we added parts to the subsystem in the competition. But it allowed us to lower the bridge perfectly all weekend.

This is exactly what we did, but our wedge was closer to the ground. It seems that the way to go would be wedges with the bridge. Their not too difficult to make, either.

[matteo2171]

We have a wedge powered up and down by a window motor the wedge is pushed back into the bumper when we hit the bridge thus holding it rigid as we lower the bridge, the advatage of it is that A you don't have to retract it to keep moving and B you have the full force of your drivetrain lowering the bridge

[Jeffy]

An easy way to make one of these work is to use a "winch-like" system. Pull the system down with a small pulley and some tether. Spring it back up. (or vise versa) It's super easy to get a very large reduction using a system like this and It is also very easy to change on the fly by adjusting the point at which the tether attaches to the arm.

[Brian Ha]

I'm sure it has been mentioned, but a passive arm is a very good way of doing it and conserving weight. We did ours with a window motor and it weighed 4 lbs. Although after watching week 1 and 2 it is getting a massive redesign. Haha it might weight a little more than 4 lbs now, but hey lets cheese away!

[flameout]

Team 957 found success with our bridge manipulator as well -- but I wanted to share it because we did not use a wedge.

We had an arm that pivoted off a spot about two inches inside of the frame perimeter. It extended close to 14 inches out of the frame perimeter, and had the Tetrix wheels from last year's minibot kit. Therefore, I'd put the lever arm from the pivot to the contact point with the bridge at about 14 inches.

We originally planned to use a Banebots RS-550 with the AndyMark Gearbox and a Banebots 256:1 P80 (rated at 85 ft-lbs), but those were out of stock when it came time to order them. Instead, after doing the math and determining that this would be acceptable (if marginal), we used a kit Fisher-Price gearbox from a previous year (no gearing between the gearbox output and the arm's input). We strapped on a potentiometer for PID control of the arm.

We used a Jaguar to operate this motor, intending to use current control through CAN to limit our maximum current output. However, we wanted to have PWM control as a backup, and tuned that loop first. After finding out how fast that arm is*, as well as how noisy the data from the potentiometer is (I think we may have had a bad pot, too, which was replaced), I re-structured the code to allow limiting the commanded speed (not just duty cycle command) and to not rely on differentiating the potentiometer's output. We then relied on the Jaguar's dynamic braking to slow the arm down (and also relied on its linearity for our control loop tuning). This removed CAN-based current control from our plans. We limited our maximum duty cycle to 30% for testing with our bridge, but were prepared to raise it for competition.

Come competition, we went out on the practice field and tested with it a bit. At 50% duty cycle, it did not effectively push the bridge down (due to lack of torque). At 70%, the Jaguar's overcurrent protection kicked in well before the bridge even made it halfway down. At 60%, it was successful in operating the bridge (note: this will probably vary based on the motor used... I don't recall off the top of my head which we used). Although this warmed up the motor really quickly, we did not need to use the arm for more than a couple of seconds at a time, so it was not an issue during our matches.

If you do choose to use a Fisher Price gearbox-based arm, I'd recommend that you be ready to spend hours testing it, rewriting code, and tuning it. Also, verify (theoretically or practically) that the exact motor you use is capable of tilting a competition-weighted bridge.

A wedge is probably quicker and more effective at tipping the bridge, but may be harder to design (especially if, like us, only a few members of your team have the math knowledge to compute the required angles to tilt the bridge and handle the generated torque). Also, our arm is capable of lifting the bridge to let balls caught under it roll out. Had our drive team (which included me, our lead driver) known where the balls were getting stuck (right on the end, where they're in the way, invisible to the drive train, and not on the ramp), we could've swept them out from under the bridge, too.

* We have a video of the arm accelerating from a stop 5 inches above our bridge to an impact with our bridge in 3 frames... at 30 frames per second. The commanded rate limitation was implemented to decrease this impact. You can find this on YouTube at http://www.youtube.com/watch?v=nXLTAL7Q3oo -- the fast motion is visible at about the 70-second mark.

[wireties]

We have yet to play - our first regional is this week. Out lowering device is a very stiff arm run by a van door motor plus a 4:1 gear reduction. It easily lowers a weighted practice bridge (with less than 50% PWM setting).

Should it work in competition?

TIA

[Sb28000]

We have yet to play - our first regional is this week. Out lowering device is a very stiff arm run by a van door motor plus a 4:1 gear reduction. It easily lowers a weighted practice bridge (with less than 50% PWM setting).

Should it work in competition?

TIA

I would have to say that this will be more than sufficient. We ran a van door motor with no additional reduction and were able to lower the competition bridge relatively easily. See my other post in this thread for details of our set-up - I just caution you to be sure your arm and mounting methods are sturdy enough and not likely to bend/deform in any way while trying to push down a bridge in a match (which we had happen to us twice).

[Ken Streeter]

This design interests me, I wish I could get a better pic of that manipulator. I'll go hunting...

Below is a somewhat better photo showing the 1519 bridge manipulator on the robot at the Granite State Regional. One of the keys to the design is that the motor alone does not hold the arm in the lowered position -- in addition to the motor, there is a servo-actuated latch which retains the arm in the lowered position so that the motor housing does not bear the load of the bridge when the robot drives into the bridge to press it down.

http://www.mechanicalmayhem.org/images/FRC-1519-NH-2012.jpg

[Phyrxes]

Depending on your design and use of "appendages" you could also use a "passive" latch using that is manually released after the match. But that would mean you are driving around with it permanently deployed if you have to manipulate a bridge early in a match.

At Chesapeake I noticed a good number of teams redesigning their bridge manipulators to either generate more force to be able to push the competition bridge down or to prevent the reaction force from damaging the deployment method.

[Steve Compton]

Here's alink to 1391 using the wheelie approach;

http://www.youtube.com/watch?v=1Rlp1-iIIus&context=C45d654fADvjVQa1PpcFOuzCcOL7utXZHXuw0IOMf-Pn6P2yG7VPE=



I watched a lot of teams (both veterans and rookies) struggle with this over the weekend. I'm not sure if the issue was more geometry or providing enough torque to the bridge to lower it.

One of the most clever methods I've seen is team 103, who has two curved pieces of tubing that flip down and so when they drive up to the bridge the natural motion of their forward momentum causes the bridge to tilt and allowed for them to get up pretty easily. It was a pretty effective, light weight and passive way of lowering the ramp without having to stop and wait for some other mechanism to push the bridge down. If I can find a pic I'll post it.

Or you could try the 25 method: bump the bridge, pop a wheelie and then get on. Seemed to work well for them :rolleyes:

[Brian_R]

I'll throw my support behind the designs from 103, 1519, and 2134 mentioned in this thread...

Us at 3710 have had some good results with a ramp-mechanism. Ours is deployed with a 4 bar mechanism to save a bit of space, but also to let mechanical stops and the chassis to bear the forces of impact with the bridge.

This has worked pretty well for a plywood test bridge (built by our buddies at 2809) and will see competition this week at Montreal - we can take the bridge at about half of our maximum speed.

We've whitepapered the design and made our CAD available - it's mostly aluminum angle and ours is bolted right on to a Kitbot on Steroids. Available here:

http://www.cyberfalcons.com/whitepapers/

[BrFrederick]

My team decided tipping the bridge was important, however the weight allocated to doing so was reduced to roughly five pounds for tipping the bridge, a ball scraper to get balls of walls and from under bridges, as well as a moveable ramp on the back of our elevator that allows balls to enter from the inbounder station.

This left me with around 2-3 pounds to tip the bridge as fast and as passive as possible. 10 designs later with the help of many free body diagrams and some tests our 2 pound tipper was born. The two pounds includes the weight of the air cylinders and everything else needed.

The result was a bar of 1by1 AL that is rotated down using a 3/4'' bore, 4 inch stroke air cylinder. Then a over center clamp is rotated over it by a 3/4'' bore , 2 inch air cylinder. Once we fixed some problems with our swerve drive software and could go straight on to the bridge it worked perfectly. However the only problem we have had with this design is currently software has a long delay before the over center will come down. So sometimes we will ram the bridge without the over center clamp on and it will not tip the bridge. However this is an easy fix.

http://i232.photobucket.com/albums/ee8/rebaler/420373_316903475033767_100001423527547_865690_1852 267896_n.jpg

[joek]

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.

we re-designed our manipulator twice, our final design is capable of holding a bridge level with three other robots pushing down with weaker devices on the other side (happened once at lake superior)

[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. :p

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]

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/hphotos-ak-prn1/539540_295212263882685_133577100046203_670315_1089 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/hphotos-ak-prn1/529514_3321613731388_1599683799_2736240_1616547560 _n.jpg

https://fbcdn-sphotos-a.akamaihd.net/hphotos-ak-ash3/562701_3321613531383_1599683799_2736239_1756691814 _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.

[Superllama12]

We were using a piston to push down the bridge, but it ended up not working because we did not have enough weight for a compressor. It definitely would have helped us at regionals, and ended up being even more important than we had expected (and we had thought it would be a very big deciding factor). We had planned for going over the bump with an eight-wheel drive system, but we kept getting caught on the frame when trying to. Maybe it was just our regional, but I never really saw anyone with a strategy that hinged on getting over the bump, except for occasionally dodging people playing defense on their side of the ramp. During the offseason, though, we will be working on the bridge mechanism.

[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!

[DavidGitz]

Our regional is next week. After watching weeks 1 & 2 we're scrambling to make a bridge manipulator:
Andymark gearmotor (KOP) on a length of c-channel with a small wheel on the end.
This is untested and will not get a chance until Thursday.
Fingers crossed!

Or use 2 andymark motors.

[Wetzel]

We made a simple static manipulator that was originally designed to only LIFT the bridge, but it turned out we were able to knock it down and get on as well. Works well enough we were picked by the 2nd seed in DC and were able to win the regional. 4.5 lbs.

I don't have a picture with me, but come find us in St Louis and I can show you in person.

Wetzel

[JewishDan18]

Team 20 had the same issue; our first design pushed down with 1 pound of force *facepalm*. It took 5 iterations, but our current design pushes down with over 140 pounds, weighs 3.5 pounds, and allows us to ram the bridge to lower it

[gracie.]

this weekend we're at the queen city regional. thanks to the amazing mechanical team we've just installed a new "ramp smacker" to lower the bridge after practice matches today. we're using a window motor and are hoping that a big gear ratio and some braces will give us the power and stability we need to push down the ramp. I'm putting on limit switches tomorrow morning and we should be fully functional!!! i've heard of all sorts of problems with the window motors, and we've had some of our own, but i'm thinking this could be a final solution.

[JohnSchneider]

Youd be surprised at the power of a winch...

I will say 100lbs of force more than brings down the bridge.

[Borobo]

what I would do is pair your window motors in a winch and pull down the arm via cable. that's what we're doing and it works great. I spend the first day of our regional perfecting the 3d 4 bar inverted ramp we had designed, only to run into problems. Instead I put together the winch arm design in a total of half an hour. It is super reliable and we can easily crush balls caught under the bridge.

[philso]

We had our winch driven arm tested in our garage last night. Today, it ended up with the motor wired up to the Spike in the wrong direction. The resultant 400 ftlb of torque turned both of the two #10 stainless steel screws pinning the home-made hubs on the pulley and the arm to the shaft into "subtle s-shapes" that had to be drilled out to get it all apart to be repaired. The other team members were amazed that the 3mm diameter Dyneema cord held up to this abuse. Its breaking strength is rated at something like 1950 pounds. We will rebuild it tomorrow with bigger bolts and a better hub design, if possible.

[JohnSchneider]

what I would do is pair your window motors in a winch and pull down the arm via cable. that's what we're doing and it works great. I spend the first day of our regional perfecting the 3d 4 bar inverted ramp we had designed, only to run into problems. Instead I put together the winch arm design in a total of half an hour. It is super reliable and we can easily crush balls caught under the bridge.

Were just using a single window motor. It all depends on your pulley size...but the force you can get from one of them is plenty. We probably have had one of the most consistent bridge pull downs at each of our regionals. Sometimes people dont think simply enough ;)

[Taylor1023]

Our coach and several members on our team were watching Week 1 matches when we started to realize just how important the bridge was. A bridge could determine who was the winner and who was ranked higher.

Our team ended up adding an "arm" after trying to balance on the bridge we made. It was originally simple with some 80-20 and a doorstop to act as a kind of brake. By the time our design team came up with the idea all the electronics had been placed and we spent some time having to rearrange when everything went since the arm would come down on the power distribution board. This was a few days before bag n tag.

It worked out well at competition and we were satisfied with how the arm worked, but a few students on our team came up with an attachment on the arm (pneumatic) to help us triple balance better (we had five pounds of weight to play with). The idea was good, but when we tried to practice balancing with it it wasn't very effective. I think our drive team used it at competitions, but not as much as we expected.

Overall, I'm glad we made the changes we did, otherwise we probably wouldn't be as successful.