any success with winches?
 

my team has been experimenting with winches from day one but have not been very lucky so far. first we tried using 2 globes driving one shaft. It should have had 150 lb/in. of torque but we could only get it 112 lb/in. at the shaft. after trying a few differant pulleys we got it to work but it was a little slower than we would have liked. then we started working with the van door motor which should have had 300 lb/in. at the shaft. we mounted the van door in a small transmission and tried it out but it stalled while trying to lift me, i weigh 140. we then tried the motor with a 2-1 reduction and it was very close to lifting me but could not do it. then finnaly we tried a 3-1 reduction and it was successfull but its a little slow. has anyone else had any success and if so could u tell me what motors your using or even better, post a picture?

thanks

Re: any success with winches?
 

Before even attempting to make ours, the engineers and I have been doing calculations on MathCAD to see what'll work and how fast it can do it. So I'll tell you whether our numbers actually reflect the real thing when it's done.

... not that we're officially trying to hang or anything ;)

Do the Math
 

O.K., here is an example:

I will use the 2 window motors, but the math works with any motor.

Tmaxp is the torque at max useable power (power just under breaker limit)
Wmaxp is the speed at the above condition
Dw is the diameter of the winch spool
Vlift is the lift velocity
Fr is the lifting force required

For our case:

Tmaxp = 4.6N-m
Wmaxp = 46 RPM
Fr = 130 lbs

We will not be using any gear ratio, just direct drive off the window motors
Equation #1: 2*Tmaxp = Fr * Dw/2 (the 2 on the torque side is due to the 2 motors)
Equation #1: Dw = 2*2*Tmaxp/Fr
Equation #1: Dw = 0.032 meters [32mm] (remember to convert lbs to Newtons)

Equation #2: Vlift = Wmaxp * Dw/2
Equation #2: Vlift = 46RPM * (2*Pi/60)rad/s * 32mm/2
Equation #2: Vlift ~ 77.1 mm/s [3.03 inches/s]


So we have a winch that can lift 130 lbs @ 3 inches/sec.

This winch could lift 1 foot in 4 seconds or 2 feet in 8 seconds.

I hope this helps.

-Paul

Re: any success with winches?
 

Okay, shameless plug time:

http://www.chiefdelphi.com/forums/pa...le&paperid=252

In the whitepaper I wrote:
Using the "Mechanism Design" worksheet in the "Design" workbook, one can easily plug and chug numbers for a winch design.

Simply input your motor specs at the top (get these from the "support" workbook), enter any speed reductions you are using, and what size pulley you want (in the torque radius box).

Plug in the "efficiency factor" and you're ready to go.

Try out different load characteristics to see how fast you will winch up, and what kind of current your motors will be drawing.



I found it useful, does anyone else? ;)

John

Re: any success with winches?
 

Hey Matt, what is the lever arm of your winch? In other words, what is the radius of the cylinder that the "rope" winds around? I'd be curious because this week I was planning on using the van door motor with winch and thought it would work well....... silly me.

thanks

Re: any success with winches?
 

I will tell you that the van door motor does work we used sprokets to change the power. we used a 5" cylinder this was done in 2000


We are using the 2 tyco motors. we cut our own gears but I bet you can find gears that would work

We are going up 18" per second we can pull over 200lbs

we are using a 6" cylinder with a bar to stop back drive. this is a one ticket up until we reset it.

Re: any success with winches?
 

18 inches per second?

Re: any success with winches?
 

Easily 18" per second. If they use the 2 CIM motors (I don't know what Tyco motors are) with a gear ratio of around 61:1 and a 6 inch spool, at 40 amps they could lift around 234 lbs (depending on efficiency ... I used .95^4) and go 18" per second. What this means is that they really are moving almost 2x that speed if another robot isn't hanging on them.

Sounds to me like someone is taking power from their drive wheels .......

Re: any success with winches?
 

If we use the drills and cims in our drivetrain what would you recomend using for the winch?

Re: any success with winches?
 

why not use the drills and cims for both?

Re: any success with winches?
 

You could use the window motors from my post earlier. Or, you could use the van door. Instead of telling you what spool size to use, I will let you figure it out with some help.

O.K., here is the van door motor torque equation:

Torque = (-34/75)*Speed + 34

Speed (angular velocity) is in RPM and torque is in N-m. At max power your speed and torque are approximately 38RPM and 17N-m, respectively. Let's assume you want to be able to pull up yourself and another robot at max power(in case your opponent is trying to hold you down) so that is 260 lbs.

Assume no gearing, just a spool right on the Van door shaft. What diameter of spool do you need? After you figure that out, then tell me how fast you would be going at max power. Then tell me how fast you would be going if you were only lifting 130 lbs.

Equations of interest:

1. Torque = Force * Diameter/2

2. Velocity = Angular Velocity * Diameter/2

After you give it a shot, I will help.

-Paul

Re: any success with winches?
 

we are using a 6" cylinder with a bar to stop back drive. this is a one ticket up until we reset it.[/quote]

We will use winch motors that can backdrive (Fischer Price) and will need a device to prevent backdriving as well. Has anybody come up with an elegantly simple way to accomplish this? We would like it to be a passive device, similar to the clutch in a manual window regulator mechanism.

We'd rather not have to use a cylinder/blocker device because of the weight. Has anybody had experience using an electrically actuated servo to move a latch pawl or something like that?

Re: any success with winches?
 

We will use winch motors that can backdrive (Fischer Price) and will need a device to prevent backdriving as well. Has anybody come up with an elegantly simple way to accomplish this? We would like it to be a passive device, similar to the clutch in a manual window regulator mechanism.

We'd rather not have to use a cylinder/blocker device because of the weight. Has anybody had experience using an electrically actuated servo to move a latch pawl or something like that?[/quote]


http://www.valleytech.k12.ma.us/robo...02%20Claw2.jpg

If you take a look at this device it is very simple to stop a motor to back drive. we use this claw to hold onto the 180lb goals and pull them around. Vey strong.

Re: any success with winches?
 

My recommendation would be to use a ratchet and pawl. These parts are easily available from many gear companies including Berg(http://www.wmberg.com/catalog/catres... oup=RATCHETS), or if you're on a really tight budget you can probably get creative with a band saw and a grinder. I would be very hesitant to rely on a mere servo to disengage the pawl. However, something like a pneumatic with a very short throw would be suitable.

Re: any success with winches?
 

We will use winch motors that can backdrive (Fischer Price) and will need a device to prevent backdriving as well. Has anybody come up with an elegantly simple way to accomplish this? We would like it to be a passive device, similar to the clutch in a manual window regulator mechanism.

We'd rather not have to use a cylinder/blocker device because of the weight. Has anybody had experience using an electrically actuated servo to move a latch pawl or something like that?[/quote]
whats wrong with a spring loaded pawl? Just look at the hand power winches they well at home depot. As mentioned above you could easily fabricate something like his with tools as simple as a a bandsaw.

Re: any success with winches?
 

I would agree that it would not be practical to disengage a pawl that was under load using just the force available in the servo. A servo could work if you take the load off of the pawl first.

Since our winch will also be used to extend and retract the ball handling device, a one time/one way ratcheting winch would be a problem. If the winch is used for lifting the robot only, a spring loaded ratchet would be fine.