📬❄️📦Adafruit Holiday Shipping Deadlines 2019: Please place all UPS 3 Day orders by 11am ET Friday December 13 📬❄️📦
0

Motor shield cutting out
Moderators: adafruit_support_bill, adafruit

Please be positive and constructive with your questions and comments.

Re: Motor shield cutting out

by johnpark on Sun Aug 23, 2009 12:41 pm

What do you mean by "touch the capacitor"? I soldered mine between the motor leads to make it a permanent fixture.

johnpark
 
Posts: 632
Joined: Wed Mar 25, 2009 2:15 pm

Re: Motor shield cutting out

by JBRobotDenn on Sun Aug 23, 2009 7:27 pm

Thanks for the reply. It is permanently fixed (it is soldered between the motor leads). Touching the capacitor with my finger makes it work (or holding it with my thumb and finger). Odd I know.
JBRobotDenn
 
Posts: 3
Joined: Sun Aug 23, 2009 10:49 am

Re: Motor shield cutting out

by johnpark on Sun Aug 23, 2009 8:36 pm

Hmm, something strange is afoot. Have you tried a different motor?

johnpark
 
Posts: 632
Joined: Wed Mar 25, 2009 2:15 pm

Re: Motor shield cutting out

by adafruit on Sun Aug 23, 2009 9:47 pm

your body has some capacitance to ground so touching it would do that.

adafruit
 
Posts: 12151
Joined: Thu Apr 06, 2006 4:21 pm
Location: nyc

Re: Motor shield cutting out

by JBRobotDenn on Mon Aug 24, 2009 11:07 am

So will bigger capacitors fix this? Any suggestions? Thanks
JBRobotDenn
 
Posts: 3
Joined: Sun Aug 23, 2009 10:49 am

Re: Motor shield cutting out

by adafruit on Mon Aug 24, 2009 3:46 pm

im wondering if perhaps you want to solder a 0.1uF from the tabs to the casing (?) this is a bit beyond my experience tho...

adafruit
 
Posts: 12151
Joined: Thu Apr 06, 2006 4:21 pm
Location: nyc

Re: Motor shield cutting out

by pstemari on Thu Jul 01, 2010 3:48 am

johnpark wrote:The brushes/bushings in a DC motor kinda skip and bounce as the motor turns. makes lots of really fast on/off connections. an upstream controller might get cranky dealing with that. (a battery wouldn't care, but looks like an L293D does)


Virtually every sort of semiconductor hates the noise off a brushed DC motor, especially the little ones with crappy brushes. The noise gets worse with load. I've had hellish problems in the past with the noise resetting the electronics, and solutions that seemed to work OK would stop working once additional load was placed on the motors.
--Paul

A wholly owned subsidiary of:
Persephone: DL R+W+B C 7 X L W C++ I++ T+ A E H++ S+ V-- F+ Q P B PA+ PL
Aldebaran: DM Rt H 5 Y L- W+ C+ I++ T++ A+++ E H++ S+ V+ F++ Q+ P B++ PA- PL--
User avatar
pstemari
 
Posts: 310
Joined: Sun Mar 21, 2010 6:10 pm
Location: Seattle, WA

Re: Motor shield cutting out

by chuckm on Thu Jul 01, 2010 1:44 pm

pstemari wrote:Virtually every sort of semiconductor hates the noise off a brushed DC motor, especially the little ones with crappy brushes.


QFT.

In Robotics, its a sign of someone who has moved beyond apprentice level who both understands and can mitigate EMI from brushed DC motors. If you're really good you can use the motor noise as a tachometer output ;-) I did this on a retrofitted toy where I could not figure out any way to put feedback from the motor to do some sort of speed control. Put one of the power leads to the motor in series with the low side of an audio transformer (100:1) and a rectifier on the other side. Brush spikes became 'tach pulses', but it would not work at low currents. Fortunately the gearbox loaded the motor enough to ensure a minimum current draw.

Motor noise suppression comes in two forms, radiated noise, and ground coupled noise. Capacitors across the motor terminals to the case can generally beat back radiated noise, and often a low inductance coil between the motor's ground and the controllers ground can block ground bounce effects.
--Chuck

chuckm
 
Posts: 159
Joined: Thu Dec 24, 2009 3:31 am

Re: Motor shield cutting out

by pstemari on Fri Jul 02, 2010 2:32 am

Well, this particular application was a photography package going up in a rocket, and the super 8 movie camera was the culprit. The 35mm with the motor drive didn't cause any problems.

I'll have to go open it up and take a look to see what I did. It was back in '95 or so when I flew it, and was using an off-the-shelf first-motion switch w latching relay.
--Paul

A wholly owned subsidiary of:
Persephone: DL R+W+B C 7 X L W C++ I++ T+ A E H++ S+ V-- F+ Q P B PA+ PL
Aldebaran: DM Rt H 5 Y L- W+ C+ I++ T++ A+++ E H++ S+ V+ F++ Q+ P B++ PA- PL--
User avatar
pstemari
 
Posts: 310
Joined: Sun Mar 21, 2010 6:10 pm
Location: Seattle, WA

Please be positive and constructive with your questions and comments.