Centrifugal Arm Claw

[couvillion]

Your post so far suggest that the timing of the release would be computer controlled. That seems really hard, and difficult to debug unless you have a high speed camera around. I would suggest that you make your release mechanical based on rotation of the arm. And the use a motor to adjust that release point forward or back. It is mechanically complex, but that can be understood without a high speed camera.

[farmersvilleRob]

Originally Posted by EricH

So it's just a back and forth launch? If it isn't, see slipring. It's more durable than a lot of slack, and eliminates any need for slack beyond what's need to plug in.

What I meant by linkage change was something like a helicopter uses for control--I believe it's called a flybar or something like that. You can do whatever you need to to the output of any non-integral gearbox. (See [R49-A])

We we're sure if sliprings were in compliance with rules. Is there anything to back it up that they are? Because that was our number one choice but we needed a backup which was the slack in the wires. Also, could you explain the flybar? I found what it basically is, but why would we need it again?

[farmersvilleRob]

Originally Posted by couvillion

Your post so far suggest that the timing of the release would be computer controlled. That seems really hard, and difficult to debug unless you have a high speed camera around. I would suggest that you make your release mechanical based on rotation of the arm. And the use a motor to adjust that release point forward or back. It is mechanically complex, but that can be understood without a high speed camera.

Well we havbelieve with an encoder (might need a better one than the FIRST choice ones) we can track the exact RPM the arm is moving at then have it correct tself before launch. It all is set to happen <2.5 sec, but we have an amazing programming team. We think the only hard part is finding how the motor corrects itself because we don't want an oscillating graph where RPM is oscillating on the y axis over the x axis of time because it's over correcting. So that's an experimental stage. We are actually hoping the cup design would be able to release the ball on a tangent to the rotation without touching the ball. If the cup is too deep, we have a shallow one and we mount the servo arms (1 cm long urethane fingertips) parallel to the x axis (perpendicular to the rotation) to also decrease chance of even bein involved in the ball's release other than the release of force.

[EricH]

Originally Posted by farmersvilleRob

We we're sure if sliprings were in compliance with rules. Is there anything to back it up that they are? Because that was our number one choice but we needed a backup which was the slack in the wires. Also, could you explain the flybar? I found what it basically is, but why would we need it again?

Is there anything to back it up? You betcha. [R44] includes the following:

The branch circuit may include intermediate elements such as COTS connectors, splices, COTS flexible/rolling/sliding contacts, and COTS slip rings, as long as the entire electrical pathway is via appropriately gauged conductors.

If you wanted to avoid a motor or servo on the rotating arm (and thereby the electrical hassle of extra wire or sliprings), you could run a setup similar to a helicopter's flybar. The flybar allows the rotor on a chopper to maintain a commanded orientation, regardless of where in the rotation the rotor is. It also translates changes up to the rotors. Something like that provides a mechanical solution to the problem (expense of weight). A slipring is probably the best option.

[farmersvilleRob]

Originally Posted by EricH

Is there anything to back it up? You betcha. [R44] includes the following:

If you wanted to avoid a motor or servo on the rotating arm (and thereby the electrical hassle of extra wire or sliprings), you could run a setup similar to a helicopter's flybar. The flybar allows the rotor on a chopper to maintain a commanded orientation, regardless of where in the rotation the rotor is. It also translates changes up to the rotors. Something like that provides a mechanical solution to the problem (expense of weight). A slipring is probably the best option.

Ah I see! So basically since We HAVE to mount the servos directly on, it would be easier to do a slipring? And we're actually mounting the encoder to the outside of the shaft so that wiring is independent then taking the shaft and in the middle of the arm we're creating a "keyed" (really just filed) section the then move with the arm. No extra anything needed it just let's the encoder sit on the outside. So then we only have 3 servos on the claw. Sorry about the grammar, but I am on my iPhone getting posts in before sleep lol

[PAR_WIG1350]

Originally Posted by EricH

So it's just a back and forth launch? If it isn't, see slipring. It's more durable than a lot of slack, and eliminates any need for slack beyond what's need to plug in.

What I meant by linkage change was something like a helicopter uses for control--I believe it's called a flybar or something like that. You can do whatever you need to to the output of any non-integral gearbox. (See [R49-A])

A swash plate? that sounds complicated, but simpler. All they would need is a nylon plate on a hinge and a matching plate on the rotor connected to the claw via a linkage, but that linkage might be tough to design. A cable with a swivel run through a hollow axle would be far simpler.

(note: don't expect that link to work until at least Thursday due to the SOPA blackout on the English language Wikipedia)

[davidthefat]

Just like Pumpkin Chunkin... http://www.youtube.com/watch?v=-1calSPjoR4

[couvillion]

I believe that swashplate would be another term for the flybar mechanism, with wiki blacked out my IQ has dropped.

In terms of timing with the release, it might be possible, but your programmer may not realize how much difficulty of real-time programming has been covered up by the WPIlib and cRIO gate arrays. I would suggest working on a backup plan at the same time.

[farmersvilleRob]

Originally Posted by davidthefat

Just like Pumpkin Chunkin... http://www.youtube.com/watch?v=-1calSPjoR4

Basically except it'll shout "Fus Ro Dah"! Lololol

But in all truth, it will be pretty quick like I said <2.5 sec maximum shot of 60'. But it'll all come down to the claw really and hopefully we can get stuff sent to the machine shop soon. And ideas on what to make the bowl design out of? We were thinking just stick with one whole piece of aluminum so the mounting is secure.

[EricH]

Yeah, that's the term I was actually looking for: the swashplate. (Flybar is similar, IIRC--I fly R/C fixed-wing, not rotary-wing.)

[farmersvilleRob]

Originally Posted by couvillion

I believe that swashplate would be another term for the flybar mechanism, with wiki blacked out my IQ has dropped.

In terms of timing with the release, it might be possible, but your programmer may not realize how much difficulty of real-time programming has been covered up by the WPIlib and cRIO gate arrays. I would suggest working on a backup plan at the same time.

Our mentor that wi be teaching us his ee skills is fairly familiar with it all so he kinda said it's possible like your saying. The only thing is we probably will get a high speed camera if their under $2000 to time the releases. It's factoring out the release time with the angle of release (which will be a set ideal angle) that's the tricky part. And hopefully it'll get to a point where the robot can either stick with an angle or adjust using our algorithm to find it's own ideal angle based on shots to correct itself.

[ToddF]

Rob,
I'm going to make a friendly suggestion. From reading your previous posts, I know you are pretty much set on a catapult rather than a wheeled shooter. You have also said a couple times that you don't have the money for prototyping. But, if you have $2000 to buy a high speed camera, you have money to prototype.

My suggestion is that you spend a couple hours putting together a single wheeled shooter prototype. It will take relatively little time and money, and may provide you a viable backup plan in case your catapult doesn't work out.

You have nearly everything you would need to prototype a single wheeled shooter in the kit of parts. To power it, use a CIM motor directly driving one of the kit of parts wheels. You'll probably need to buy some stuff (1/2" keyed shafting, 1/8" keys, a motor to shaft coupler) from McMaster Carr. With overnight shipping, this stuff will probably come to less than $100.

Just so you know, our team also is hoping to use a catapult style shooter. But, we're working on it knowing that if there are unexpected difficulties, we have a workable fall back plan.

[farmersvilleRob]

Originally Posted by ToddF

Rob,
I'm going to make a friendly suggestion. From reading your previous posts, I know you are pretty much set on a catapult rather than a wheeled shooter. You have also said a couple times that you don't have the money for prototyping. But, if you have $2000 to buy a high speed camera, you have money to prototype.

My suggestion is that you spend a couple hours putting together a single wheeled shooter prototype. It will take relatively little time and money, and may provide you a viable backup plan in case your catapult doesn't work out.

You have nearly everything you would need to prototype a single wheeled shooter in the kit of parts. To power it, use a CIM motor directly driving one of the kit of parts wheels. You'll probably need to buy some stuff (1/2" keyed shafting, 1/8" keys, a motor to shaft coupler) from McMaster Carr. With overnight shipping, this stuff will probably come to less than $100.

Just so you know, our team also is hoping to use a catapult style shooter. But, we're working on it knowing that if there are unexpected difficulties, we have a workable fall back plan.

It was more in joke about the camera but we'll still have a backup shooter, we're just worried about the blind variables that are really hard to control. And like every system has them but the catapult just has less it seems.