15-01-2010 16:50

zachjo

Re: pic: 2010 window motor winch

How many lbs can it theoretically lift?

15-01-2010 18:40

Jones571

Re: pic: 2010 window motor winch

Nice cad model some specs would be cool our window moder winch never left paper

15-01-2010 18:43

Chris is me

Re: pic: 2010 window motor winch

I like the use of COTS parts. How are the window motors mating with the Toughbox?

15-01-2010 18:50

Joe Johnson

Re: pic: 2010 window motor winch

And equally important, how long will it take to lift you?

The window motors are basically 20W motors. This is pretty good but not with respect to the FP (almost 200W) and CIM (just shy of 340W).

Watts matter because speed and torque are just accidents of birth -- you can trade one for the other. Not fast enough, trade away some torque, get more speed. Need more torque, gear it down, give up speed, get some torque.

BUT... POWER is what it is. The peak power of a motor only goes DOWN when you gear up or down, it never gets MORE powerful.

If you are trying to lift a 120lbs motor 3ft in 10 seconds -- that means you need 54 Watts. If you only have 40Watts (the best you can do with 2 window motors at 12V) then you are not going to do that much work (lifting the robot that high) in that amount of time... ...no matter how you gear things...

For what it is worth.

Joe J.

15-01-2010 18:50

Mr_I

Re: pic: 2010 window motor winch

At 12.75 : 1 ratio, you might get 200 ft-lb torque ( ), but only 6.5 rpm.

15-01-2010 19:15

Tom Line

Re: pic: 2010 window motor winch

Joe, that is the singularly best expression I've ever heard about how to pick a motor. I never thought about the torque vs. speed being an accident (not really an "accident" because you know what type of rotational inertia etc you'll end up with, but I know exactly what you mean).

I also never thought about looking at a motor from the energy side of things. I've always been more statically oriented, so I looked at torque - can I do it at that speed.... but the energy calculations make it a whole lot easier.

A light bulb just went on. Don't you love it when that happens?

15-01-2010 19:29

Taylor

Re: pic: 2010 window motor winch

Perhaps this winch isn't designed to lift 120 lbs...

16-01-2010 00:25

Iceman1330

Re: pic: 2010 window motor winch

@Joe, thanks for the information.

To preface all of this, the winch was designed before I did any gearing calculations, I was just futzing around with solidworks and thought it might be interesting to put up on CD.

The winch was indeed designed as a main robot winch and was designed primarily to fulfill these criteria.

• Not back-drivable
• Cheap
• Minimal amount of machining capability
• Lifts above platform in 20 seconds
• Doesn't involve a powered "release" mechanism (such as a latch or pawl)

With regards to speed: It isn't important that it does it quick. The winch is designed to be a bolt-on-bolt-off lifting arm package should the robot require it. All that the team needs from a winch is the design criteria above.

Perhaps you could offer an alternative method? I've racked my brain but everything I can think of is either difficult to implement, costly, or a mixture of the two.

EDIT: So it looks like it could raise itself close to 5 feet in 20 seconds if operating at 40W peak the entire time, correct? (and of course presuming correct gear ratio for that)

@Chris- AM 8mm hubs. The window motor hubs have the 1/2" shaft section ground off (or lathed) such that a hub can attach to them. This is of course presuming that the input gear to the toughbox isn't easily retrofitted to a non 8mm shaft.

16-01-2010 15:48

mplanchard

Re: pic: 2010 window motor winch

Beautiful SolidWorks model. Dont forget to count the Mass for your fasteners. But nuts/bolts all in a folder so you can suppress/unsuppress them. In the FeatureManager, right-click Add Folder. Then drag and drop your fasteners into the folder.
You can also enter total mass of the assembly under Tools, Mass Props, Assign Mass Properties. Marie

17-01-2010 12:48

frc295

Re: pic: 2010 window motor winch

our team has already prototyped this design minus the gear box and it can lift 120 lbs, but not fast. i would imagine putting a gearbox would a) help it because it would allow for more torque, therefore the motors can spin more freely b) make it too slow to hang in the last 20 seconds. those 2 motors running at 10 watts max a piece made it past the platform in about 10 -15 seconds

17-01-2010 12:59

MrForbes

Re: pic: 2010 window motor winch

We're looking into making a dual window motor winch to power a kicker, and using the 5th CIM to lift the robot. Window motors are not very powerful for lifting a robot, but they are powerful enough to pull 50-100 lbs a short distance in a couple seconds to shoot a ball.

17-01-2010 13:19

gorrilla

Re: pic: 2010 window motor winch

wouldn't how fast it lifts the robot depend on the size of the spool?

So if you had a 4inch diameter spool then it would pull in roughly 12" of cable each revolution, so if it's spinning at say, 60rpm, then it would pull in around 720" per minute or 12" per second?

Should work the lift the robot 72" in 6 seconds?..

17-01-2010 13:53

MrForbes

Re: pic: 2010 window motor winch

The diameter of the spool affects the time it takes to take in a certain amount of cable, but it inversely affects how much force you apply to the cable. So if you use a larger spool, it winds faster, with less pulling force (assuming the same motor and gear ratio driving the spool).

17-01-2010 14:11

the man

Re: pic: 2010 window motor winch

Easy fix use two sim motors

17-01-2010 14:17

rsisk

Re: pic: 2010 window motor winch

I have to agree with Tom about the great explanation from Joe, but, show some mercy on a software guy and explain the formula use to calculate the 54W below.

TIA

17-01-2010 14:37

sanddrag

Re: pic: 2010 window motor winch

I'll take a shot at it. Work = Force*Distance. Power=Work/Time. So, say we are trying to lift 120lb to a height of 3 feet. Then you need to do 360lbf-ft work to it. To do this in 10 seconds, you need 36lbf-ft/sec of power. There are 550lbf-ft/sec in one Horsepower. There are 746 Watts in one horsepower. So, you need about 49 Watts to make this pull. If you consider the force required to accelerate the robot from zero to loaded-line-pull speed, and inefficiencies and whatnot, more power will be required.

17-01-2010 14:46

Vikesrock

Re: pic: 2010 window motor winch

Here's one way I came up with 54W:


120lbf * 3ft = 488 J (Work = Force*Distance, there's a conversion factor from lbf-ft to J in here as well. Google Calculator did this conversion for me)
488J/ 10s = 48.8W (Power = Work/Time)
48.8W / .9 = 54 W (Gearbox efficiency)

From what I remember reading here and erring on the side of caution I would use 80% as the gearbox efficiency yielding 61W of power necessary.

Also be careful using 120lb as a weight. A full 120lb robot this year could end up at over 150lb after adding battery and bumpers. Using 150lb and 80% efficiency you need about 76W of power to complete the lift in that time.

17-01-2010 14:50

the man

Re: pic: 2010 window motor winch

But you have to account for the bumpers and batt