Re: Window Motor question
 

Neither, The faster motor would simply slow down, if it is running in tandem with the other motor their speeds would have to be the same.

Re: Window Motor question
 

So, we did some math, correct me if any of this is wrong:

Our cylinders are 4 in diameter, so piD=4pi=~12

Therefore, the "gear ratio" of the twine winding is 12:1.

A Window Motor, at stall torque is 1501 oz/in. Change that to 125, since we are "gearing" it up by 12.

Now we are at only 125 oz of torque. That is roughly 8 pounds. Consider the grabber weighs six, and the other stage 4 lbs. Thats 10, and that is why our motor is stalling.

If we are running at 10 amps, this is about halved.

Like I said, correct me if any of this math is incorrect.

With this info, we now know that two motors would provide roughly double the torque, bringing us to 20 lbs, easily enough. If only we had done this math earlier :(

On the other hand, we still have the question of why is the motor running at 10 amps, and stalling, when it shouldn't stall until later. If we put two motors on, will they just stall at 10, and we only get 10 lbs of lifting force?

Re: Window Motor question
 

There is no gear ratio involved in the drum. Simply a smaller drum will apply more force and a larger drum less force.

Your torque is in oz-inches. Now correct me if my math is wrong...

If your arm is 10 lbs then for torque you need 10*16 160 ozs. across a 4 inch drum it would be 160*4 = 640 oz-inch.

Re: Window Motor question
 

I think it would be 160*12, since you want the circumference not the diameter.

Re: Window Motor question
 

You want the radius because of the lever arm.

And to your earlier question about the stalling motor.

Your current and weight numbers match the torque/ force output of the curves. Are you sure the Thermal breaker inside the motor isn't being tripped which would cause your arm to stop moving.


Edit: So with a 2 inch drum. You're motors are actually producing 320 oz-inches of torque to pull a 10 lb load.

Re: Window Motor question
 

Wait, im not sure either of us are understanding each other:

For each rotation of the winch, the grabber rises 12 inches on the ladder. When it reaches the next stage, it pulls that up with it.


We are not using it as a lever, as in a traditional arm, but in a system of pullies, which eventually makes it raise up.

I drew you a picture! Excuse the poor visual.


Consider something with a 1 in shaft pulling in a 10 lb weight. It needs to turn 12 times to get a foot. Every turn has an amount of torque.

Consider the same motor with a 12 in shaft, pulling the same weight. It now needs to turn once, and that one turn has 1/12 the torque.

Re: Window Motor question
 

The amount of force applied to your ladder/winch system is dependent on the size of the drum. A larger drum will pull the ladder up quicker but require more force. A smaller drum will require less force but it will be slower.

Torque is a measurement that includes Force and a distance. If I am spinning the drum at 320 oz-inch it will take 320 oz at 1 inch to stop the drum from rotating or 160 oz at 2 inches since it is only applying a force of 160 ozs at 2 inches.

You're throwing pi in there which is ok as long as you take it out again...

And I'm assuming there are no reductions in the pulleys.

Re: Window Motor question
 

I see!

I guess I wasn't properly going to torque, I was just going directly to how many pounds of force the motor needs to exert to pull our assembly up.

BTW, thanks for you help tonight, its really been...helpful.

You are correct, there are no reductions in the pulleys.

Re: Window Motor question
 

An additional thought here.
If you have surgical tubeing pulling your lift down... take it off, the motor will have to work harder and harder the farther your arm goes up. The much better way is to have the winch work as a capstan winch, where the cable only loops around the drum a few times, then attach the cable to the bottom of the lift, in that manner the winch pulls the lift up, then pulls it down if needed. In either case you have full winch power to pull with.

The quickest fix would be a smaller drum, that may mean making a whole new drum, but it would likely help you a lot, and be less weight.

For example, if you change from a 4" diameter drum to a 2" diameter drum you double your pulling power on your winch cable. with no additional weight!!!

you should be careful of minimum bend radii on your cable though.