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Steel
01-27-2006, 03:40 AM
I have 2 stepper motors being powered by 9 volts and controlled by a BS2 through a Transistor Array.

...Both the motors are functional.

...I am mounting the motors one (sideways) on top of the other so that I can point anywhere on an X-Y Axis.

My Problem?· The bottom motor (that is holding the other motor) is not strong enough to hold the other motor and move.· When I send it commands, it vibrates as though it is trying to step...but alas...isn't able to make it to the next step.· I am sending high-torque commands to it (%0011, %0110, %1100, %1001).

...The motors I am using are these:
http://www.allelectronics.com/cgi-bin/item/SMT-65/400600/SMALL_STEPPER_MOTOR_W_6_LEADS_.html

Has anybody worked with this similar set up before?· I have seen the Laser Controller with Servos, but servos are too expensive for this application.

I guess I am looking for smaller motors with as much strength, or just a more efficient stepper motor.

*Note...they need to be purchased from a supplier...not 'Scavenged'.

Thanks

Paul Baker
01-27-2006, 03:52 AM
Steel said...


I guess I am looking for smaller motors with as much strength, or just a more efficient stepper motor.

These unfortunately are·contradictory terms, the problem you'll find with the smaller steppers found on surplus sites is the torque is not provided as a parameter. This leaves you with not much of an alternative to buying a bunch and testing them.
You can try to use a higher voltage to drive them since this would produce more torque but you need to be careful because you may end up burning one out. Sorry I can't provide more detailed advice, you could look for a retail motor, but you listed cost as a key criteria. You may want to investigate if hooking a unipolar motor up as a bipolar provides more/less torque (I think it my be less though).

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·1+1=10

PJ Allen
01-27-2006, 03:55 AM
http://www.goldmine-elec-products.com/prodinfo.asp?number=G14781&variation=&aitem=1&mitem=1

Steel
01-27-2006, 04:17 AM
^^ Do the goldmine motors have the torque to push/hold it's own weight?

Beau Schwabe
01-27-2006, 04:57 AM
Steel,

With the proper gear ratio, you could lift a car with a 9V battery.... What you are asking is vague, and greatly depends on how much
of a lever arm and/or mechanical linkage you have.

If this is a similar project to my laser pointer (http://forums.parallax.com/showthread.php?p=549166) and you want a cheaper solution (i.e. no servos). Instead of looking for a more powerful
stepper, look for a gear reduction that will work with your existing stepper.

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Beau Schwabe (mailto:bschwabe@parallax.com)

IC Layout Engineer
Parallax, Inc.

Post Edited (Beau Schwabe (Parallax)) : 1/26/2006 9:19:48 PM GMT

John R.
01-27-2006, 05:13 AM
Balance is also a factor. With an "arm" one assumes an over-hanging weight. You may be able to help the situation by a counterbalance. While this adds total weight/mass to the stack, the fact that the weight is balanced should make things easier to turn. Bearings and other alignment aids can also make a huge difference.

I guess the big message from Beau and myself is that "torquier" motors may not be the only way to solve your problem.

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John R.

8 + 8 = 10

Beau Schwabe
01-27-2006, 05:48 AM
Steel,

Thinking about it further, you might want a gear reduction anyway..... Since most Stepper motors have a 1.8 Deg step, that's 200 steps for 360 deg.



Looking back at my project, my range of motion to cover 8ft is only about 50 Deg.

Projected Distance = 9ft
Span Left to Right = 8ft

Bisecting my Left to Right span to form two right triangles 4ft by 9ft by 9.85ft <--- sqrt ( 4ft^2 + 9ft^2)

Sin@ = Length of Opposite side / Length of Hypotenuse

Sin@ = 4ft / 9.85ft

Sin@ = 0.40609

@ = 23.96 Deg

multiplied by a factor of 2 I get 47.9 Deg ..... or 50 Deg


Now, why all the math and why is this important? In a similar setup, using a Stepper with 1.8 Deg per step this would only give you
a resolution of 27 steps ( 50 Deg / 1.8 Deg). Divide that by an 8ft wall span, and your pointer will move about 3.6 inches per Stepper Unit. ..... (12 * 8ft) / 27 = 3.6

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Beau Schwabe (mailto:bschwabe@parallax.com)

IC Layout Engineer
Parallax, Inc.

Post Edited (Beau Schwabe (Parallax)) : 1/26/2006 9:52:23 PM GMT

PJ Allen
01-27-2006, 11:14 AM
After the invention of the fulcrum and lever, Archimedes wrote, "Give me where to stand, and I will move the earth."

Bean
01-27-2006, 11:20 AM
Steel,
· Two ways to get more torque.
· 1st is to move slower. Stepper have greatest torque at the slowest speed.
· 2nd is to use R-L drive. http://www.allegromicro.com/techpub2/compumot/a23a28.pdf
· R-L drive is basically raising the drive voltage and putting a resistor in series with each coil. Because the coils have a large impedance when power is first applied to them, the voltage across the coils will higher, causing them to energize faster. (read the pdf link)
Bean.

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Steel
01-28-2006, 01:04 AM
Thanks guys. I am going to continue researching it. Unfortunately Mechanics aren't my strong point, so I am going to have to sit down and take some more time looking into it.

Again, thanks for the replies.