go_away

Author Topic: I/P torque unit?  (Read 3706 times)

0 Members and 1 Guest are viewing this topic.

Offline airman00Topic starter

  • Contest Winner
  • Supreme Robot
  • ****
  • Posts: 3,653
  • Helpful? 21
  • narobo.com
I/P torque unit?
« on: October 16, 2008, 12:30:16 PM »
Regarding wheelchair motors it says the following:
Quote
    *  24 volts (good)
    * 70 amps peak, 14 amps continuous (use a Vantec RDFR23 speedcontroller)
    * 15 pounds (a little heavy for lightweight, best for a middleweight)
    * 125 rpm (perfect)
    * torque 125 I/P (fine for robot purposes)
    * shaft diameter is 0.83 inches with double flats (the flats are useful, but the diameter is odd).
    * overall dimensions are 14 inches long, diameter of motor is 3 inches, and the gearbox is about 4 inches high.


What is 125 I/P ? I looked online but I don't see anything about I/P relating to torque. Maybe inches/pound ? But shouldn't it be pounds per inch?
Check out the Roboduino, Arduino-compatible board!


Link: http://curiousinventor.com/kits/roboduino

www.Narobo.com

Offline ArcMan

  • Supreme Robot
  • *****
  • Posts: 519
  • Helpful? 4
  • Mmmm... Plasma
Re: I/P torque unit?
« Reply #1 on: October 16, 2008, 12:35:25 PM »
It's probably inch-lbs. (a measurement of torque).  It's seems a bit low for a wheelchair gearmotor, but it's in the right neighborhood.

BTW, the shaft diameter is probably really 21 mm (which is ~ 0.83").  Almost all wheelchair motors that I've seen have metric shafts.
« Last Edit: October 16, 2008, 12:38:29 PM by ArcMan »

Offline airman00Topic starter

  • Contest Winner
  • Supreme Robot
  • ****
  • Posts: 3,653
  • Helpful? 21
  • narobo.com
Re: I/P torque unit?
« Reply #2 on: October 16, 2008, 02:18:26 PM »
This might sound stupid but whats the difference between 125 lbs per inch and 125 inches per lb ? Is it the same amount of torque?

Also
if there are two wheelchair motors going in the same direction on the chassis does that mean there is 250 I/P of torque in total or does the chassis only have a torque of 125 I/P?
« Last Edit: October 16, 2008, 02:22:20 PM by airman00 »
Check out the Roboduino, Arduino-compatible board!


Link: http://curiousinventor.com/kits/roboduino

www.Narobo.com

Offline ArcMan

  • Supreme Robot
  • *****
  • Posts: 519
  • Helpful? 4
  • Mmmm... Plasma
Re: I/P torque unit?
« Reply #3 on: October 16, 2008, 03:06:10 PM »
This might sound stupid but whats the difference between 125 lbs per inch and 125 inches per lb ? Is it the same amount of torque?
Also
if there are two wheelchair motors going in the same direction on the chassis does that mean there is 250 I/P of torque in total or does the chassis only have a torque of 125 I/P?

Doesn't sound stupid.
The units are actually pronounced "inch-pounds".  If you want to get really technically correct, the unit is supposed to be lbf-in (pounds force inches). But I digress.
in-lbs. are a measure of torque.  Think of it like this.  If you attached an arm 1" long to your shaft and suspended a 125 lb. weight to it while the arm was horizontal, it would lift the weight.  Likewise, a 10" arm could lift a 12.5 lb. weight.  Or a 10" diameter wheel (5" radius) would produce 25 lbs. of "thrust".
Using 2 motors will, of course, double your chassis torque to 250 in.-lbs.


Offline airman00Topic starter

  • Contest Winner
  • Supreme Robot
  • ****
  • Posts: 3,653
  • Helpful? 21
  • narobo.com
Re: I/P torque unit?
« Reply #4 on: October 16, 2008, 03:32:17 PM »
Standard electric wheelchairs have 12" wheels(6" diameter) so that means that each wheel has only 20.83 lbs of force? So a total wheelchair has only 41.66 lbs of force?

How on earth is that possible if the people sitting on the wheelchairs weigh over 200 lbs ? Shouldn't the torque be at least 200lbs @ 6" (12" diameter wheel) ?


EDIT: Shouldn't it be 125(lbs/in torque) * 6 ( radius of 12" wheel in inches) = 750 lbs of torque . Even that sounds a little wrong since the torque is so high.

Can someone clarify this for me?
« Last Edit: October 16, 2008, 05:29:12 PM by airman00 »
Check out the Roboduino, Arduino-compatible board!


Link: http://curiousinventor.com/kits/roboduino

www.Narobo.com

Offline madchimp

  • Robot Overlord
  • ****
  • Posts: 158
  • Helpful? 2
Re: I/P torque unit?
« Reply #5 on: October 16, 2008, 07:04:53 PM »
How on earth is that possible if the people sitting on the wheelchairs weigh over 200 lbs ? Shouldn't the torque be at least 200lbs @ 6" (12" diameter wheel) ?

If it were lifting the person yes but it takes a lot less force to roll something then to lift it. Ever have to push a car? I will use a mini cooper for an example even at 2,500lb it rolls pretty easy on a flat surface.  It has 114 ft/lbs of force which according to google 114 foot pounds = 1368 inch pound force just to put things in perspective. It's 0-60 is 8.5 seconds. Hope that helps a little I don't know all those formulas but I know it helps me to have something I'm more familiar with for an example.

Offline Ro-Bot-X

  • Contest Winner
  • Supreme Robot
  • ****
  • Posts: 1,431
  • Helpful? 25
  • Store: RoBotXDesigns.ca
Re: I/P torque unit?
« Reply #6 on: October 16, 2008, 07:11:00 PM »
ArcMan explained corectly. A 2" diameter (1" radius) wheel will be able to move 125 pounds. This is the maximum weight the motor can produce at it's rated voltage. To calculate the the weight for a biger wheel radius, divide the max weight by the number of inches the radius is equal to.

Now there is the rolling factor to take into consideration. The motors may be under-rated because the motor doesn't have to put up the same effort to move the same weight on a rolling platform on a level surface. If there is an incline...  the effort raises to be equal to the max for a 90 degree (vertical) incline. The only thing that the motor has to overcome is the momentum (at start and stop).

Madchimp beat me to answer this...
Check out the uBotino robot controller!

Offline airman00Topic starter

  • Contest Winner
  • Supreme Robot
  • ****
  • Posts: 3,653
  • Helpful? 21
  • narobo.com
Re: I/P torque unit?
« Reply #7 on: October 16, 2008, 07:44:11 PM »
OK I think I understand a bit more

So lets assume the chassis has two motors and each motor has 125 I/P and has a 12" diameter wheel. That means each motor has a force of 20.83 and the whole chassis has a force of 20.83*2 = 41.66 lbs of force

Now the weight of the robot is as follows : 30 lbs for both motors , another 40 for two big lead acid batteries. Thats a total of 70 lbs not including the weight of the actual material on the chassis. How does that 70 lbs of downwards force of weight affect the  force in the horizontal direction?
Check out the Roboduino, Arduino-compatible board!


Link: http://curiousinventor.com/kits/roboduino

www.Narobo.com

Offline Ro-Bot-X

  • Contest Winner
  • Supreme Robot
  • ****
  • Posts: 1,431
  • Helpful? 25
  • Store: RoBotXDesigns.ca
Re: I/P torque unit?
« Reply #8 on: October 17, 2008, 05:41:39 AM »
Adds momentum. Objects tend to resist change in motion. A static obkect would resist to being moved and a moving object would resist stopping. The greater the weight, the greater the momentum.

On the other hand, I don't think those motors had 12" wheels. I have seen wheelchairs or better say scooters that have smaller diameter wheels, probably for bigger wheels the motors are stronger.

To use the motors for pulling up a leg you need to stay within the limits of the max specifications, since it is not a rolling platform anymore.
Check out the uBotino robot controller!

Offline airman00Topic starter

  • Contest Winner
  • Supreme Robot
  • ****
  • Posts: 3,653
  • Helpful? 21
  • narobo.com
Re: I/P torque unit?
« Reply #9 on: October 17, 2008, 08:07:49 AM »
Found this information. It is my wheelchair motors exactly . The values are slightly different than the previous information I posted.

Quote
a.. Peak Rated Power Consumption 560W
b.. Rated Voltage DC24 V
c.. Rated Current 11.5 A
d.. Rated Torque 16.5 Nm
e.. Rated Speed 166 RPM
f.. Efficiency at Rated Speed & Torque 52%
g.. Peak Current 65 A
h.. Peak Torque (at 70A) 55.4 Nm
i.. Gearbox Ratio 1/28
j.. Minimum Brake Torque 2 Nm
k.. Maximum Brake Release Current 0.4 A
l.. Mass 6.9 kg
m.. IP Rating IP50
n.. Noise 65 db(A)

What strikes me as strange is that right now I am running Chives on one 12V 20aH battery and I don't think I've ever experienced the 65A peak , since that would probably kill the relays(rated at a maximum of 30A) and the relays are still working to this day! Whats even more strange is that this peak didn't occur even when I stood on top of the platform and took it for a ride ( before I put on the body of Chives on the chassis I had some fun , :P ) . Could it be that since I ran it at 12V everything got divided by two? Does that mean my torque at 12V is 1/2 of my torque at 24V?
Check out the Roboduino, Arduino-compatible board!


Link: http://curiousinventor.com/kits/roboduino

www.Narobo.com

Offline Ro-Bot-X

  • Contest Winner
  • Supreme Robot
  • ****
  • Posts: 1,431
  • Helpful? 25
  • Store: RoBotXDesigns.ca
Re: I/P torque unit?
« Reply #10 on: October 17, 2008, 05:57:43 PM »
Power = Voltage * Current

So, for half the voltage, at same current, you get half power.

Rated torque is 16.5 N*m which is equal to 146.037299992 lbf*in at a rated current of 11.5 A and rated voltage of 24 V. This seems most likely to be the real deal with your motors. Peak rating is the maximum that you can get from the motors before they burn out. So, 55.4 N*m translates to 490.331298154 lbf*in at 70 amps!!!

You can see now how these motors can easily move even a fat person around...

Edit: conversions done with: http://www.unitconversion.org/unit_converter/torque.html
« Last Edit: October 17, 2008, 05:58:45 PM by Ro-Bot-X »
Check out the uBotino robot controller!

Offline airman00Topic starter

  • Contest Winner
  • Supreme Robot
  • ****
  • Posts: 3,653
  • Helpful? 21
  • narobo.com
Re: I/P torque unit?
« Reply #11 on: October 18, 2008, 02:27:17 PM »
how do I calculate how much current the motor draws based on the weight of the robot?
Check out the Roboduino, Arduino-compatible board!


Link: http://curiousinventor.com/kits/roboduino

www.Narobo.com

Offline Admin

  • Administrator
  • Supreme Robot
  • *****
  • Posts: 11,657
  • Helpful? 169
    • Society of Robots
Re: I/P torque unit?
« Reply #12 on: October 19, 2008, 04:41:41 AM »
Quote
Shouldn't it be 125(lbs/in torque)

Its lbs * in, not lbs/in ;D

Just use this calculator to see if its reasonable for your robot:
http://www.societyofrobots.com/RMF_calculator.shtml

Quote
how do I calculate how much current the motor draws based on the weight of the robot?

http://www.societyofrobots.com/energy_calculator.shtml
http://www.societyofrobots.com/mechanics_energy.shtml

That'll give you watts (joules/sec) . . . so just use Power = Voltage * Current to get amps.

Offline airman00Topic starter

  • Contest Winner
  • Supreme Robot
  • ****
  • Posts: 3,653
  • Helpful? 21
  • narobo.com
Re: I/P torque unit?
« Reply #13 on: October 19, 2008, 06:02:46 AM »
Well what happens at 12V ? Is everything halved , including torque?
Check out the Roboduino, Arduino-compatible board!


Link: http://curiousinventor.com/kits/roboduino

www.Narobo.com

Offline Admin

  • Administrator
  • Supreme Robot
  • *****
  • Posts: 11,657
  • Helpful? 169
    • Society of Robots
Re: I/P torque unit?
« Reply #14 on: October 19, 2008, 06:06:25 AM »
Quote
Well what happens at 12V ? Is everything halved , including torque?
You need to check the motor datasheet for voltage/current/torque curves . . . if you can't find a datasheet, the only way you can know is from experimentation.

Offline Ro-Bot-X

  • Contest Winner
  • Supreme Robot
  • ****
  • Posts: 1,431
  • Helpful? 25
  • Store: RoBotXDesigns.ca
Re: I/P torque unit?
« Reply #15 on: October 19, 2008, 06:20:19 AM »
Well what happens at 12V ? Is everything halved , including torque?

Probably so, but the motor may draw more current so the torque may be around 3/4 of the rated value. But for sure the RPM will be around half.
Check out the uBotino robot controller!

 


Get Your Ad Here

data_list