DPRG mailing list archives: [DPRG] Pittman GM8712 stats

Tue Sep 4 14:39:36 CDT 2001

Excellent data David!  I read the data into Excel and 
plotted DC voltage vs. Ticks/sec.  VERY linear as expected.

I have some experiments that you (or someone else)
may want to try:

1) Do the numbers match if you reverse the polarity?
  (In other words, do the motors give the same speed for
   the same voltage in reverse?)

2) I'd like to see some experimental (empirical) data to
  verify the recent theoretical discussion of PWM vs. true
  applied voltage.  In other words, what % of PWM value do
  you need to get the same speeds when using 19.1V as the
  source voltage.  Example: What PWM % value do you need
  to get 434 ticks/sec (=4.0V DC) if you're switching between
  0V and 19.1V?  [Be sure to note PWM frequency.]

3) Again using 19.1V source voltage, what is the motor speed
  at different PWM frequencies given the same PWM duty cycle?
  (Example: Always 25% but 200Hz, 500Hz, 1kHz, 2kHZ, 5kHz, 10kHz)

				- Dan Miner

PS - I may have to break down and buy some of these motors
even though I keep telling myself I should first use up some of
the robot "parts" I've already accumulated!  ;-)

> -----Original Message-----
> From: David P. Anderson [mailto:dpa at io.isem.smu.edu]
> Sent: Tuesday, September 04, 2001 1:52 PM
> To: dprglist at dprg.org
> Cc: seattlerobotics at yahoogroups.com
> Subject: [DPRG] Pittman GM8712 stats
> 
> 
> Howdy
> 
> I made some measurements this weeked with the single channel home-brew
> encoder on a Pittman GM8712 gearhead motor.  I used an encoder wheel
> with 20 segments: 20 ticks per motor revolution, as per:
> 
> ftp://www.geology.smu.edu/pub/users/dpa/robo/pittman/home_brew
> _enc_01.jpg
> 
> and
> 
> ftp://www.geology.smu.edu/pub/users/dpa/robo/pittman/home_brew
> _enc_02.jpg
> 
> I verified and adjusted the sensor spacing with a scope, then 
> connected
> it to an M.I.T. 6.270 board (HC11) and used the TIC3 interrupt to
> count encoder ticks per second, which I printed on the LCD.  I used a
> DC bench supply to power the motor, with a multimeter to measure the
> voltage and current.  Here's what I got:
> 
> ---------------------------------------------------------------------
> motor_speed.txt
> 03 Sept 01
> dpa
> 
> Pittman GM8712 with 20 segment encoder
> No-load measurements
> 
> Voltage	Current	 Ticks	Motor	Gearhead
>   V  	 A	per/sec	 RPM	 RPM
>                         
>  19.1 	1.4 	2641	7941	132
>  15.0	1.4	2050	6156	102
>  12.5	1.3	1658	4980	 82
>  10.0	1.2	1302	3906	 65
>   7.5	1.15	936	2808	 46
>   5.0	1.0	570	1710	 28
>   4.0	1.0	434	1302	 21
>   3.0	0.9	288	 864	 14
>   2.0	0.8	156	 468	  7
>   1.5	0.75	 84	 252	  4
>   1.2	0.75	 37	 111	  1
>   1.1	0.75	  0	   0	  0
> 
> 
> ---------------------------------------------------------------------
> 
> regards,
> dpa