Supporting 40lbs Arm with Motor?

[Ether]

Originally Posted by kevin.li.rit

I think he meant you can an stop the movement of an arm or other mechanism by running the motor opposite to the current rotation.

Let's wait and see.

[TheKeeg]

Originally Posted by Ether

Would you please explain what you meant by this?

http://www.chiefdelphi.com/forums/sh...80&postcount=3
Rather than switching the direction, it is shorting across the terminals. Sorry for the misunderstanding.

Originally Posted by Ether

It sounds like what you are describing is for your launch catapult arm. If so, how do you disengage the gearbox from the winch when you fire it?

Well our system is a little bit different. We have a transmission as described that does not shift. That transmission pulls back the winch to any desired start point and we have a brake system that holds the catapult in position while the winch unwinds to the desired hard stop length. Then the lock that I described in the previous post comes in. We did this to eliminate the need for a two speed transmission.

[Ether]

Originally Posted by TheKeeg

That transmission pulls back the winch to any desired start point and we have a brake system that holds the catapult in position while the winch unwinds to the desired hard stop length.

So when you said in your previous post that "we mounted a sprocket on the end of our winch. There is then a pin that inserts in the teeth/grooves of the sprocket" you did not mean that the sprocket was connected to the winch, but rather to the arm? So the winch can unwind while the arm is locked in place by the pin and sprocket?

...the winch unwinds to the desired hard stop length.

Are you saying that the winch acts as as the hard stop? Is the impact load transferred to the gearbox?

[TheKeeg]

Originally Posted by Ether

So when you said in your previous post that "we mounted a sprocket on the end of our winch. There is then a pin that inserts in the teeth/grooves of the sprocket" you did not mean that the sprocket was connected to the winch, but rather to the arm? So the winch can unwind while the arm is locked in place by the pin and sprocket?



Are you saying that the winch acts as as the hard stop? Is the impact load transferred to the gearbox?

No. The sprocket is mounted on the winch. There are two brakes/locks. One on the winch and one on the catapult. The Winch lock with the pin and sprocket engage whenever the winch is not moving so that it cannot back drive. When the catapult is locked in position, the winch can unwind. The load is on the axle, but it is very supported.

[Ether]

Originally Posted by TheKeeg

There are two brakes/locks.

Ah. There's the missing puzzle piece. What does the catapult lock look like, and how do you release it?

[TheKeeg]

Originally Posted by Ether

Ah. There's the missing puzzle piece. What does the catapult lock look like, and how do you release it?

I cannot release a picture yet, but we drew inspiration from one way bearings. The brakes use the rotation of the catapult to their advantage, and with a little mechanical advantage and pneumatics, they are easy to release.

[Ether]

Originally Posted by TheKeeg

I cannot release a picture yet...

When and if you are free to do so, I think it would be most interesting to see what your team has done

[TheKeeg]

Originally Posted by Ether

When and if you are free to do so, I think it would be most interesting to see what your team has done

Will do.

[cmrnpizzo14]

Originally Posted by nrogals

Both units will weigh about 20lbs.

Are you saying that both of them together will weigh 20 pounds or that they each weigh 20 and together they are 40?

[Uriah]

Originally Posted by NOV8R

we have a similar weight shooter/arm. Ours is counterbalanced with a gas lift spring like the ones used on car hoods. The arm itself is powered by a banebots 256:1 gearbox connected to a 18 tooth Gates pulley driving a Gate belt around a 50 tooth pulley welded to the arm. Works well .

256:1 Wowza.

We have a similar system, and are using a 49.4:1 gear box with a mix of pnuematics. We did have problems with friction, but some lithium grease and letting the system wear in helped.

[TheKeeg]

Originally Posted by Ether

When and if you are free to do so, I think it would be most interesting to see what your team has done

This is what the brakes look like:

http://www.chiefdelphi.com/media/photos/39541?

[Ether]

Originally Posted by TheKeeg

This is what the brakes look like:

http://www.chiefdelphi.com/media/photos/39541?

Great idea !

Is the brake spring-loaded in the brake_on (or brake_off) position?

Or is the cylinder powered in both directions?

[IndySam]

Originally Posted by TheKeeg

This is what the brakes look like:

http://www.chiefdelphi.com/media/photos/39541?

Westinghouse would be proud.

[TheKeeg]

Originally Posted by Ether

Great idea !

Is the brake spring-loaded in the brake_on (or brake_off) position?

Or is the cylinder powered in both directions?

It is a dual-acting cylinder. In the picture the brakes are not engaged.