Winch for a steep ramp.

[sacharlie]

Been in search of a small 12v winch that uses a nylon strap instead of a cable. Haven't found anything with a strap or as small as I would like. So I've found Bruno scooter lifts have such a winch with strap that depending on model will dead lift 200~400lbs. These can be found used for $300~450. I may go for that but would like to ask just what torque these gearmotors on the scooter lift would have.
The reason is I've found new AME 90~120rpm wiper gearmotors with 24~30 in-lb stall torque for $55~65 at the robot market place. Mounting a spool on one would be easy.
Thanks

[woodygb]

torque.JPG

[woodygb]

but would like to ask just what torque these gearmotors on the scooter lift would have

Unknown and not really relevant .... you just wish to move the scooter/chair up an incline/slope in a reasonable time.
Gearing being the factor that effects everything .

So ...how heavy ( mass ) ...how far ( distance )...how quickly ( time ) and the slope angle?

[sacharlie]

Thanks but help me with that formula.
If Lift=TorqueXradius or 200x1=200lbs lift
if the radius is now 2" then 200x2=400lbs lift.
You move 1 inch further away from the shaft and the lift increases? Shouldn't it decrease?

[sacharlie]

I'm looking at: 250lbs over 10ft at 1ft rize over 1.5ft run (67%).

[woodygb]

Simplified

The angle of your ramp is 34 degrees

Pull required to shift your 250 lbs up the ramp = 250 * 0.53 ( sin 34 degrees ) = approx 135 lbs of pull

Torque required ( lbf - inch ) = 135 lb's divided by the pulley radius in inches.

Remember that your pulley size will increase as the strap wraps around it.

[sacharlie]

Thanks You.
So if I put a spool with a 1" radius on the motor shaft to starting torque will need to be 135 divided by 1 = 135 lbft or 1620 in lbs. If the spool has a 2' radius to start it would 135 divided by 2 = 67.5 lbft or 810 in lbs.
Also the required torque would decrease as the radius would increase a the strap wound around the spool. Now I have #s to work with.

The theory is relation to a motor shaft has got me though. I see the above as a man with a lever turning a shaft taking less force from the man to turn the shaft as the lever gets longer. With that said it seems the lever attached to a motor shaft serves as the radius and as the radius/lever gets shorter less force would be needed from the motor but more force crom the man.

I know I am confused. I do have a mechanical device book I will have to dig into.

[sacharlie]

Another way to look at what I'm trying to say.
Picture a 6" spool with a 1" center core and a crank handle at the out edge which is the same as having a 6" lever. The radius of the 1st turn is 1/2" and when the spool is full the radius is 3". If you were to dead lift 100lbs by hand would not the 1st turn of the empty spool take less force than the last turn when full spool?

[Burgerman]

Yes.

[ex-Gooserider]

You are correct, though I'm not sure of the exact formulas - given a constant torque output from the motor, you will get less force as the shaft diameter gets bigger. Think of it as trying to stop the motor from turning by grabbing a lever attached to the shaft - the further out you are on the lever, the less pressure you will need to stop the motor...

I think Woodygb is not using quite the right formula (or needs to solve it for a different variable) in his answer earlier - I would assume that his initial answer on how much force is needed (note that this is a minimum, it won't hurt to have more) is correct, in which case you will need to find a motor that will produce AT LEAST that much force at the point when the spool is full (i.e. at it's maximum diameter)

ex-Gooserider

[LROBBINS]

With the ramp shorter than the chair, the chair will never actually be climbing a slope as steep as the ramp itself. Your torque needs will be less, espeically at the very top and bottom.

[woodygb]

I think Woodygb is not using quite the right formula (or needs to solve it for a different variable)

DOH!

Times NOT Divide.

Torque = Force TIMES Radius!

[sacharlie]

I think Woodygb is not using quite the right formula (or needs to solve it for a different variable)

DOH!

Times NOT Divide.

Torque = Force TIMES Radius!

Well that sure DO make a difference...LOL.
I'll need a bigger motor. Thanks

[Step]

Question:

Why does it have to be with a strap?
car winches with a cable are commonly available, pretty cheap, very strong and quite small. I had one in an old WAV to pull me in my manual chair into the back.
You could fix a strap to the hook if it is to protect your chair.

[sacharlie]

I may end up using a ATV or boat electric winch if I can find a small one. The boom type hoists used to lift scooters and powerchairs into minivans have winch motors that look the size of wiper motors but they must have some additional gearing inside the booms to multiply the torque; they list some up to 400lbs lift. The gearmotors I've found on the robot parts sites have no where near the torque to do that.

[Martin O Refurbisher]

Why not motorise something like:

http://www.autow.com/winches/manual-win ... ches-strap

As you say, a small wiper type motor should do.

Best,

Martin

[ex-Gooserider]

I suspect that motorizing a hand crank winch would be non-trivial, however it seems to me that most of the electric winches with cable are designed with capacity for a LOT of cable - often 30-50' or more... Since this application only needs a few feet of strap, I would probably be more inclined to look at trying to adapt a cable winch drum to use a strap instead of the cable. Or if the issue with a cable winch is wanting to avoid the splinters and such that go with a steel cable, it might also work and be an easier conversion to replace the cable with a good quality nylon or poly rope... In addition, seems like any of the electric winches that I've seen would have plenty of strength to handle the load.

ex-Gooserider