Supporting 40lbs Arm with Motor?
 

Hello Everyone,

Our team is looking to put a long rage shooter and acquisition unit on a single arm. Both units will weigh about 20lbs. The torque on the motor will be near 70-80 foot pounds.

Can a Mini CIM and a multiple stage gear box hold the arm up via friction in the gear box. If not, is there a method for running the motor with a certain voltage pattern such that it holds the arm and will not pull a sufficient amount of power away from the drive train.(Electric Break)

If not, at last resort, does anyone have any suggestions to apply a mechanical break to the motor shaft.

Thanks!!!!!

Re: Supporting 40lbs Arm with Motor?
 

How is the motor coupled with your arm? 80ft lbs is a lot of internal friction.

Perhaps you can add counterweights, springs or use a screw mechanism to rotate your arm.

Re: Supporting 40lbs Arm with Motor?
 

If possible try to counterweight or otherwise balance the arm so the motor is only moving the arm up and down and you are not stalling the motor to hold the arm in position.

Given the numbers from your post this isn't going to be an easy solution, you may wish to look at gas shocks and other more robust methods of accomplishing this.

Good luck!

Re: Supporting 40lbs Arm with Motor?
 

Why not simply spring load the rear of your shooter so that it takes some of the load off from the motor? Gravity will assist on the way down to acquire, and the spring will assist to get you started back up.

Re: Supporting 40lbs Arm with Motor?
 

Worm gear drive?

Re: Supporting 40lbs Arm with Motor?
 

The elastic is a good idea and the simplest. You could also drive the arm with a screw. It will give you your mechanical advantage with out back driving. Use a Love Joy between your screw and gearbox output shaft.
http://www.mcmaster.com/#spider-couplings/=qn2jdu
http://www.mcmaster.com/#acme-precis...screws/=qn2k15

Re: Supporting 40lbs Arm with Motor?
 

I'd highly recommend counterbalancing the arm somehow, either with weight or with some form of spring. If you can't, then you could look into a worm gear to hold the arm in position. Weather a multi-stage gearbox can hold it is entirely dependent on the specifics of said gearbox.

Re: Supporting 40lbs Arm with Motor?
 

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 .

Re: Supporting 40lbs Arm with Motor?
 

If the arm only rotates one direction, it may be possible to use a ratchet and pawl.

If not +1 on the spring loading. 1" diameter surgical tubing does wonders.

Re: Supporting 40lbs Arm with Motor?
 

Some of you may remember Team Driven's Pizza Box from GKC, Razorback and World Champs, the box weighed 40 or so pounds and we had to use a worm gear box and dual miniCIMs with a 32:1 reduction to lift it. This is a very challenging feat to accomplish. You will not be able to do it with all but the toughest of planetaries with a massive reduction. A banebots 256:1 P60 is only rated at 36 (IIRC) foot pounds of torque and you just double that. Worm gear with a substantial reduction is the way to go.

Worm gears can be ordered to be back drive proof, but beware, cast iron gears can (and will) shatter if they take a shock load (like a sudden hit from your arm being rammed). We had to custom make bronze gears to alleviate this fault

Re: Supporting 40lbs Arm with Motor?
 

Well to answer your question...yes you can have the motors on brake where it switches directions rapidly so that you cannot back drive. I don't really know your situation, but I know window motors have an internal locking mechanism (to stop thiefs).
We have a RS-775 12 attached to a 1:100 reduction and we mounted a sprocket on the end of our winch. There is then a pin that inserts in the teeth/grooves of the sprocket when we want the motor to brake (not back drive). The 775 will also be on brake when the winch lock in engaged.

Re: Supporting 40lbs Arm with Motor?
 

Check out the KOP page and Vulcan Springs. Their constant force springs are an easy way to add a counter balance and can significantly reduce the load you need to break.

BTW They respond quickly and even give you free shipping, great company!

Re: Supporting 40lbs Arm with Motor?
 

Would you please explain what you meant by this?

Re: Supporting 40lbs Arm with Motor?
 

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.

Re: Supporting 40lbs Arm with Motor?
 

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?

Re: Supporting 40lbs Arm with Motor?
 

Let's wait and see.

Re: Supporting 40lbs Arm with Motor?
 

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

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.

Re: Supporting 40lbs Arm with Motor?
 

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?

Re: Supporting 40lbs Arm with Motor?
 

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.

Re: Supporting 40lbs Arm with Motor?
 

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

Re: Supporting 40lbs Arm with Motor?
 

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.

Re: Supporting 40lbs Arm with Motor?
 

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

Re: Supporting 40lbs Arm with Motor?
 

Will do.

Re: Supporting 40lbs Arm with Motor?
 

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

Re: Supporting 40lbs Arm with Motor?
 

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.

Re: Supporting 40lbs Arm with Motor?
 

This is what the brakes look like:

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

Re: Supporting 40lbs Arm with Motor?
 

Great idea !

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

Or is the cylinder powered in both directions?

Re: Supporting 40lbs Arm with Motor?
 

Westinghouse would be proud.

Re: Supporting 40lbs Arm with Motor?
 

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