Dear DAVID Community,

In 2016, DAVID and this forum have been integrated into HP Inc.
This forum has been read-only since then, and will be switched off by then end of 2019.

To everyone who has contributed here, we thank you for all your work and for the constructive, helpful and friendly atmosphere you have created!
Please continue to discuss on the HP Support Forums.

Interesting Motor Problem

Interesting Motor Problem

Postby Eoghan » Wed Sep 01, 2010 9:16 pm

Hey Guys,
I wonder if any of you geniuses can explain something to me.
I have this motor
http://radionics.rs-online.com/web/sear ... 36&x=0&y=0
The Motor is connected to a 250:1 gearbox.
As you can see its rated for 12 V
I wanted to do a test for planeless scanning so I gave it a very simple sketch, using a duemilanove and the adafruit motor shield. Move forward 4000 steps in Interleave mode, wait two seconds, move back 4000 steps, wait two seconds, repeat.
I was powering it from the usb port so it was well under powered but still fine for moving the laser.
I marked the position of the laser on a wall at top and bottom of each sweep, and left it running for over an hour. It never missed a step ! Always in the same position. Perfect !
I now decided to give it the correct voltage and tested again. It is now continuously missing steps. I would say as much as 200 steps for every forward and backward movement.
I know I could possibly compensate for this in the software but I'd really like to know why at the correct voltage it is doing this but at 5 v it is working fine.
Any Ideas ?
Eoghan
 
Posts: 21
Joined: Thu Feb 11, 2010 3:31 pm
Location: Dublin, Ireland

Re: Interesting Motor Problem

Postby WalterMo » Wed Sep 01, 2010 9:16 pm

Hi Eoghan,
Strange thing. Because I have never used the Adafruit motor shield I genned up on it:
http://www.ladyada.net/make/mshield/use.html

There is written:
„Don't connect the motor power supply to the 5V line. This is a very very very bad idea unless you are sure you know what you're doing!“

They recommend:
„If you would like to have the Arduino powered off of USB and the motors powered off of a DC power supply, plug in the USB cable. Then connect the motor supply to the PWR_EXT block on the shield. Do not place the jumper on the shield. This is a suggested method of powering your motor project.“

Walter

P.S. If the motor driver IC becomes too hot at 12V, then reduce the voltage to 9V. It's only important to use a high voltage at high speeds.
User avatar
WalterMo
Moderator
 
Posts: 2363
Joined: Mon Apr 02, 2007 6:52 pm
Location: Braunschweig, Germany

Re: Interesting Motor Problem

Postby Eoghan » Wed Sep 01, 2010 9:16 pm

Thanks Walter,
I think they are referring to the 5v breakout on the shield but I'm not sure. For safety though I have hooked back up a 12v supply as per their directions. Strange thing is it has been running fine now for about an hour at 12v . I'm beginning to suspect gear slippage is happening inside the gearbox. If I change my motor speed for the return sweep it starts to miss steps. Perhaps my pinion is misaligned. It's a sealed unit so it's difficult to know for sure. Will have to dismantle and get my calipers out. :?
Eoghan
 
Posts: 21
Joined: Thu Feb 11, 2010 3:31 pm
Location: Dublin, Ireland

Re: Interesting Motor Problem

Postby WalterMo » Wed Sep 01, 2010 9:16 pm

But before you dismantle the combo you should change the software and the hardware a bit like I had done it here:
viewtopic.php?f=6&t=1827&start=15
User avatar
WalterMo
Moderator
 
Posts: 2363
Joined: Mon Apr 02, 2007 6:52 pm
Location: Braunschweig, Germany


Return to Hardware

Who is online

Users browsing this forum: No registered users and 2 guests