Bridge device failure fix

[Donut]

We finally got to use our bridge manipulator today and found that you don't actually need all that shallow of an angle to get the bridge down. While I would certainly advocate a design like this if you have the room, we have a wedge that extends out around 7" but down 12" and still works (something like a 50 or 60 degree angle). You need a bit of a running start to make sure the bridge gets down well but we've balanced once in practice today and numerous times on the practice field with this so far.

Of course it may not hold up for an entire regional of beating, but we'll know that at the end of Saturday.

Also for teams throwing something like this on last minute, you don't have to use a motor to drive it if you have no other appendage outside the robot. We have a hinge and bungee cord to flip out the wedge as soon as the robot moves and it hangs out the entire match. Saved us the weight of a motor and the time of getting it hooked up.

[Brandon_L]

Originally Posted by Donut

We finally got to use our bridge manipulator today and found that you don't actually need all that shallow of an angle to get the bridge down. While I would certainly advocate a design like this if you have the room, we have a wedge that extends out around 7" but down 12" and still works (something like a 50 or 60 degree angle). You need a bit of a running start to make sure the bridge gets down well but we've balanced once in practice today and numerous times on the practice field with this so far.

Of course it may not hold up for an entire regional of beating, but we'll know that at the end of Saturday.

Also for teams throwing something like this on last minute, you don't have to use a motor to drive it if you have no other appendage outside the robot. We have a hinge and bungee cord to flip out the wedge as soon as the robot moves and it hangs out the entire match. Saved us the weight of a motor and the time of getting it hooked up.

We found it will work with a larger angle, but it works smoother/doesn't require a head start with a smaller angle.

[nitneylion452]

Originally Posted by Brandon_L

We found it will work with a larger angle, but it works smoother/doesn't require a head start with a smaller angle.

Theoretically, this will work with any angle 0 < x < 90.

[Kevin Sevcik]

We came up with this around week 2. Only mistake was direct driving it with a PG71. Worked fine on the practice bridge, but the real thing would've laughed at it. So we're running on a 256:1 P60. After shearing pins, replacing them with PG71 pins and then shearing sun gears, we put a latch on it. Otherwise it works good. An interesting point is that the angle has relatively little effect on the holding torque necessary, unless your pivot is well above 12".

[beiju]

Our team had that in our first regional, but we still weren't able to lower the bridge. I assume it's lack of torque in our drive train, but I want to get other opinions.

We're using 6-wheel drive, with KOP Traction wheels in the center and omni-wheels for the other four. Each side is driven by one CIM (which I think is our problem) into a CIMple box, and the chains are all 1:1 ratios. Another problem was that a last-minute shooter design change forced us to move the arm to the side, and we couldn't afford the weight of a second arm (connected so as to not violate the one appendage rule) on the other side. We plan to fix both of those problems for our next regional, and I hope that will allow us to easily lower the bridge.

[Brandon_L]

Originally Posted by beiju

Our team had that in our first regional, but we still weren't able to lower the bridge. I assume it's lack of torque in our drive train, but I want to get other opinions.

We're using 6-wheel drive, with KOP Traction wheels in the center and omni-wheels for the other four. Each side is driven by one CIM (which I think is our problem) into a CIMple box, and the chains are all 1:1 ratios. Another problem was that a last-minute shooter design change forced us to move the arm to the side, and we couldn't afford the weight of a second arm (connected so as to not violate the one appendage rule) on the other side. We plan to fix both of those problems for our next regional, and I hope that will allow us to easily lower the bridge.

Ours is a two cim drive, I cant say for sure but I think that could be our problem. A lower angle on the triangle would probably be best, its less resistance.

[AllenGregoryIV]

Originally Posted by beiju

Our team had that in our first regional, but we still weren't able to lower the bridge. I assume it's lack of torque in our drive train, but I want to get other opinions.

We're using 6-wheel drive, with KOP Traction wheels in the center and omni-wheels for the other four. Each side is driven by one CIM (which I think is our problem) into a CIMple box, and the chains are all 1:1 ratios. Another problem was that a last-minute shooter design change forced us to move the arm to the side, and we couldn't afford the weight of a second arm (connected so as to not violate the one appendage rule) on the other side. We plan to fix both of those problems for our next regional, and I hope that will allow us to easily lower the bridge.

Are the chains really 1:1 from the CIMple box? With 6" wheels that's geared for about 25 ft/sec, that is very fast and with only 1 CIM per side that is a very small amount or torque. The kit drive train reduces 12 to 26 out of the CIMple box and that provides a bit more torque. My team goes 12 to 36 with two CIMs per side to make sure we have enough torque.

[philso]

beiju

Our team had a similar device mounted off to one side of a wide robot. It was not very effective. The drive train has 4 CIM motors each driving a Mechanum wheel. The robot would pivot toward the other side when the bridge pusher contacted the bridge. We concluded that only the two motors on the side with the bridge pusher were contributing thrust towards pushing the bridge down. We are in the process of replacing it with a sturdier device that is mounted in the center and powered by a geared-down van door motor. Our weight estimates show that we should be able to install a second pusher arm on the shaft of our mechanism.

One of the reasons for gearing down the van door motor is to get greater torque. This may allow us to help balancing by holding the bridge up and lowering it slowly, damping the sometimes violent oscillations. The other reason is to slow down the motion of the mechanism so that the limit switches have time to work. The first one that our team built was directly powered by a window motor. It would come down with a loud "whack". It eventually destroyed the limit switch. The motor only had to rotate about 90 degrees to deploy the mechanism and at 84 rpm, that takes only a fraction of a second. It is quite possible that the damage to the old arm was self-inflicted when it smashed into the end stops.

[notmattlythgoe]

I'd be interested to know how you get a 20 degree angle with sides of 14 and at least 8?