Window motor or FP W/ Gearbox?

[swwrobotics]

Originally Posted by Coffeeism

How far and how fast do you need it to move?

Also very important, what is the size of your spool?

What is the size of the rope on the spool?

We want our arm to move pretty fast, and we have tried the window motor but it was really slow. The spool size for the window motor was a pvc pipe about 1 inch in diameter and 22 inches in length to fit the width of the robot.

[PAR_WIG1350]

Originally Posted by swwrobotics

We want our arm to move pretty fast, and we have tried the window motor but it was really slow. The spool size for the window motor was a pvc pipe about 1 inch in diameter and 22 inches in length to fit the width of the robot.

A one inch spool will be slow even with an FP and gearbox. The larger the spool the less force you can pull with, but with the benefit of a faster pull.

[kevin.li.rit]

You can bump it up to a 3 inch spool with a single FP and gearbox and it will move pretty quick. Should cover the 22 inches in little over a second.

[pfreivald]

I suggest that you consult your local physics teacher or mechanical engineer. He/she can teach you the relationship between power, torque, and angular speed -- and how to convert that into a linear time on a 22-inch pull.

With the torque/power specifications of a particular motor/gearbox combination, you will then have all the tools necessary to make the right decision for the application.

[kevin.li.rit]

Originally Posted by pfreivald

I suggest that you consult your local physics teacher or mechanical engineer. He/she can teach you the relationship between power, torque, and angular speed -- and how to convert that into a linear time on a 22-inch pull.

With the torque/power specifications of a particular motor/gearbox combination, you will then have all the tools necessary to make the right decision for the application.

22lbs * 1.5 inch lever arm for a 3 inch spool = 33lbs*inch=528 oz*inch

528oz*inch / 121 (reduction in FP gearbox) = 4.33 oz*inch

RPM @ 4.33oz is approximately 19000RPM at motor, 157 RPM at output.

24 inches/s assuming 100% efficiency after the motor output.

Using specs for the 801-0673 FP

[pfreivald]

Originally Posted by Coffeeism

22lbs * 1.5 inch lever arm for a 3 inch spool = 33lbs*inch=528 oz*inch

528oz*inch / 121 (reduction in FP gearbox) = 4.33 oz*inch

RPM @ 4.33oz is approximately 19000RPM at motor, 157 RPM at output.

24 inches/s assuming 100% efficiency out of the motor output.

Using specs for the 801-0673 FP

I was talking to the OP, sorry... I was hoping they'd learn something about torque, power, and speed!

[StevenB]

I've written a document that attempts to explain how to use the motor spec sheet and do the appropriate calculations: http://www.botsnlinux.net/firstphysics.php. There are also a lot of other great resources here on CD about selecting the right motors and doing force/torque calculations. Search around, especially in the CD-Media white paper section.

Finally, don't just decide based on your gut or what people here say. Do the math and be sure for yourself!

[Hawiian Cadder]

While the FP and gearbox has much more torque than one window motor, keep in mind the complexity of building a winch for that gearbox. If you use two window motors, one on either side of the winch, then you can build a winch with only 2 parts. We made a winch with a housing of a single piece of 4*2 tubing, and a single winch drum. It "winches" with around 140 lbs of force when both window motors reach stall.

[Jeffy]

Since it hasn't been mentioned-
Keep in mind that the window motors have a thermal shutoff that at times can seem to shut off prematurely. We use window motors for bridge lowering and use them twice a match, but teams have run into trouble with constant movement using window motors (ie. swerve steering).

Also keep in mind that window motors and jaguars don't mix well. (lets not debate it here, do a little searching)

One last consideration- Window motors are anti back drive and FP's are not.