Low cost motor scanner

[WalterMo]

I found an interesting low cost stepping motor with an attached gear at Pollin:
http://www.pollin.de/shop/dt/Mjc1OTg2OT ... 2_038.html

This unit is also available from All Electronics (CAT#SMT-107) in the U.S.A.:
http://www.allelectronics.com/make-a-st ... ors/4.html

It's a bipolar one with a step angle of 1.8°. The impedance of the coils of the two phases is rather low with 6.5 Ohms each. Therefore it's necessary to use a low supply voltage for the driver not to overheat it. I have tested the built-up motor scanner with the EasyDriverV3 and with a driver board from Markus Mechatronics.
http://www.watterott.com/EasyDriver-v3- ... tor-Driver
or
http://www.markusmechatronics.com/index_eng.html
and then click on „Driver selfbuild kit“.

Both drivers are microstep ones and were used in 1/8 step mode. The supply voltage was 7.5V. Additionally a heatsink was glued with an epoxy resin adhesive onto the IC A3967 of the EasyDriver. The SMD potentiometer on the EasyDriver board was turned to left to its output current minimum of 150mA.

The gear around the stepping motor isn't performed with its cogwheels in one physical line but with three different endings. Unfortunately no output shaft is available. The ending with the highest gear ratio (17:1) is used to pivot the laser. As you can see on the photo a copper sleeve is glued directly with an epoxy resin adhesive at the helical cut cogwheel and a tube with a knurled screw is clamping the laser.
In the 1/8 microstep mode the laser has a resolution of 0.013° per step.

As a controller for the driver an Arduino microprocessor or a clock generator like this can be used:
http://www.david-laserscanner.com/forum ... 9462#p9462
The direction of rotation must in the last case additionally chosen by a toggle switch (Gnd or +5V to the DIR input).

The newest version V4 of the EasyDriver has some advantages over the former V3. E.g. a more robust potentiometer, the possibility to change the step subdivision and to power down the output stage.


All the best for the new year and have a lot of fun with DAVID!

Walter

P.S. Take care not to give clock rate impulses or the direction signal to the inputs of the EasyDriver when its power supply isn't switched on. By neglecting this I have just damaged the DIR(ection) input of an EasyDriver.

Edit 1: Here you can find how to connect a stepper motor via the EasyDriverV3 to an Arduino:
http://www.david-laserscanner.com/wiki/ ... re_project

And also here:
http://www.david-laserscanner.com/forum ... 366#p12366

Edit 2: In the meantime I have made a test in planeless scanning with this device. You can find it here in my second post of Jan 16th :
http://www.david-laserscanner.com/forum ... 405#p10405

Edit 3: You can also control this stepper scanner by the Arduino and the Adafruit motor shield on it:
http://www.david-laserscanner.com/forum ... t=30#p8155

[RAYA]

Walter

Seems that this system has low backlash also with comparing it with worm gear system.

Ray

[funtasma]

Nice device for a real good price! Unfortunately all motor drivers you recommend are sold out in the moment
So I have to wait to experiment with other parts....

[WalterMo]

You are right, EasyDriver V3 and V4 are not available at present at Watterott.

Markus Mechatronics, whose board I prefer, is just on Christmas holidays. This driver has more power, a heatsink can easily mounted, and it's safer to handle. A disadvantage is that the „kit“ comes only with the printed board and the IC TA8435HQ.

Walter

[WalterMo]

The question was, would it be possible to use this low cost scanner even for planeless scanning?

I have tried it with my self-made wooden Atomium on a turntable. And I think the result is acceptable.
To avoid backlash I have simply stretched a rubber band from the laser to the baseplate.

Details:
Pro9001, Green Laser, 8 table positions à 45°, 800x600 pixels @ 20fps, Poisson 300 fusion. Each single scan was 1x interpolated, but not smoothed.
Advanced settings: UseRememberPlanePoses = True

Walter

[WalterMo]

And now as an untextured Flash. New Poisson fusion with a 200-resolution. And then mesh density reduced with MeshLab.
(From about 48000 to 6000 faces).

[middyeasy]

Howdy,
After reading your post i went ahead and bought two of these to try out.. Im using an arduino with the adafruit motor controller where i hooked up the A and B coils like you have indicated in your picture and hooked it to M1 and M2... when i send the M command.. the motor just sits there locked up and hums. I was wondering if you ran into a situation during your setup where it did this and perhaps explain an situation that it would do that so i can trouble shoot the problem on my adafruit.



Thanks and thanks for posting the link.

Ken

[WalterMo]

Hi Ken,
We can get a locked and humming stepper if the frequency of the clock rate is too high. That means higher than about 500 Hz.
Or if the motor shaft is blocked. Or if a bipolar motor is used where an unipolar is requiered or vice versa.
Or if only one of both phases is connected, or if only one of both output stages is working.
You see, there are a lot of "ifs".
The output transistors are sensitive and can be damaged by hight voltage spikes. They can occur when the motor is connected or disconnected when the driver board is supplied by its power supply. So switch this off before!

I have never used an Adafruit motor shield on my Arduino, only the two motordriver boards mentioned above. So I don't have any experience in this.
Looking around on the web I found this site:
http://www.ladyada.net/make/mshield/use.html

There is an example program for bipolar or unipolar steppers. And they have used the double-ports M3 and M4. Perhaps you try it in the way they suggested.

Walter

[tailele]

this is a fantastic idea.....i have a question..is it necessary arduino to move the stepper motor???

i have find another stuff, but i don't know if this motor is right...it is a micromotor that work in ac to 12 v...this motor can turn to 1/3 rpm to 12 v. If the micromotor work with 6 v, is it possible to reduce the velocity?

[WalterMo]

No, it's not necessary to control a stepper motor by the Arduino. You can also use e.g. this circuit (May 11th):
viewtopic.php?f=9&t=919&start=30

The signal on the left side, comming from an opto-coupler is a feature, but not necessary.


Your chosen 12V DC motor can be used down to about 4V. And the speed will be decreased to about 1/9 rpm (= 40° per min.). That means to scan an object over e.g. 20° needs 30 sec. That's too fast for a Web Cam at a higher resolution.

[tailele]

ok....i have found a motor with reduction that do 18° in one minut...220v...could it be right?
then next week i'll buy to david site a ccd camera b/w...for scan a chair, what lens can i buy?6mm is it right?

[WalterMo]

Normally a 220V AC motor cannot be caused to change its direction by changing its pins. Only a few of them are able to do this by changing the pole of a third wire. Check if the motor has more than 2 wires!
18° in one minute should be ok. Of course best is to have some reserves.
Perhaps you can reduce the speed by a factor of two by using a diode in series. By making 25Hz from the 50Hz of the mains. I will check this possibility.

A 6mm lens is right to scan a chair. For a very small object like a coin I would prefere a 12mm lens, works only in combination with an extension adapter.

Edit: That with the frequency halving doesn't work. Of course not, the needed current inversion isn't given.

[tailele]

yes...i cannot change direction...so i do it manually....but, can i reduce with a diode the velocity or not?

[WalterMo]

No, you are committed to only one speed. See my "Edit" above.

Better is to use the DC motor with gear, which you presented above, and add an additional gear. Such a DC motor enables much more flexibility regarding speed and rotation direction.