I Need Help With An Arm

[Team ICE #1611]

We are rookie team and could use some suggestions and possibly some help for designing an arm for our robot this year. We have come up with a few ideas but we would like to know what others are doing so we can get an idea and build off of it. Our idea for an arm right now is being based of the forklift and use pneumatics and/or motor to power it. If anyone has another idea for us or can help us with our own we could sure use it.

[team222badbrad]

I would say the easiest thing to build a forklift with is 8020. www.8020.net

This depends on how much equipment/resources you have build with.

If you do a forklift you definitely need to use a motor to move it up and down.
You can use either cable, chain, or a rack & pinion to move it up and down.

You will also need 3 stages to obtain the height you need to reach the center tetra.

[Swampdude]

There's another thread on here http://www.chiefdelphi.com/forums/sh...threadid=33082

In it is a video of team 121 documenting there progress. They apparently didn't mind showing there concepts to the world. So I doubt they would mind you taking the liberty of the concept shown. You should probably ask anyway. But personally I think the wood 2 joint arm mock-up concept is a great idea, and could be built pretty easily. It's my opinion to stay away from elevators. I think they're too slow and top heavy. What ever you do, keep your center of gravity low. There's threads on telescoping arms, which could be a great easy way to go also.
All that said, if you're feeling like an arm may be more than you're ready to build. There are some excellent defensive strategies that you could design to, that let you place tetras inside of goals instead of on top, and focus more on a good drive system to block and offend. Every alliance will need a good bully. It's also my opinion that the kit is so good, this year it may boil down to the best drivers, and not the equipment. Every year has shown you can do a LOT with nothing more than a rolling chassis, and this year will be no different. I would focus more on getting done quick and giving your drivers as much time as possible to get used to it.

[Alex1072]

Some things to think about off the top of my head:

center of mass - Make sure to make your forklift as light as possible relative to you drivetrain; otherwise your robot will be very top heavy and trip.


Pnumatic vs. Motor: Pnumatics cannot give you precise control of the position of the arm. With pnumatics you are either extended or retracted (and maybe a middle position). Also, with a large cylinder you may run out of air if you use it too often. On the other hand pnumatic implementations tend to be lighter then motors because you can use on compressor to drive a lot of actuators. Also, you do not have to deal with a converting rotational motion to linear. If you use chain and sprocket, make sure the chain is big enough and tensioned enough so that it will not slip. If you use cables make sure they do not jam/rip on edges.


Balanced loads: Make sure that you do not drive your forklift from only one side (assuming it has sides). If you do that, it may have a tendency to get jammed becuause it will tilt.


good luck

[dhitchco]

Some other general advice from one rookie to another. Think about the following:

1) The "arm" really only needs to extend about HORIZONTALLY 2.5 feet beyond the front edge of the robot in order to be hovered over the center of a goal

2) The "arm" may or may not need its own independent rotating/turning mechanism depending on how well you build your drive base assembly. Namely, can you position a tetra by using a "stiff arm" and rotating the whole robot at its base?

3) The arm needs to get to three different VERTICAL positions only. One is floor-height to pick-up a tetra on the field (either the vision tetras or one that got dropped), second is a tetra at "loading" height (manual load or auto-load) and the third height is the height required to TOP another goal or stacked tetra. No need to get to any other heights.

4) The robot "arm" most likely needs to be able to judge by itself when it is safe to "drop" a tetra onto a goal. It will be very difficult to see if the robot is in position from the driving station.

So.....think about your arm in a cast. What MINIMUM number of functions does the arm need to have?