Low Cost Servo Motor Tester from eBay

For about a $1.50 USD eBay sellers will ship out to you the servo tester pictured above.   It's an amazing value to let you verify that the cheap servo you also got from eBay even works.  It's also great to help understand the MIN, CENTER, and MAX positions for any servo based RC or uC project. 
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Basically, servos motors are controlled by receiving pulse train signals.  The eBay servo tester is capable of producing this required pulse train.  Jameco has an easy to follow tutorial.  The image below shows that a 1mSec pulse width sends the servo full left.  1.5mSec centers the it.  2mSecs move the servo full right.  Jameco explains it all very well.

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The servo tester has three setting:
     MANUAL: allows the servo position to be adjusted with a knob.
     CENTER:   sets the servo to it's center position
     SWEEP:     continually sweeps the servo from it's MAX to MIN position (forever)

Connection is simple.  One side of the servo tester is for power.  The other side is where the servo under test conveniently plugs in.
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So.... let's use a Tektronix MSO5104B oscilloscope to look at the output of the servo tester and see what the heck is going on.  In the screen shot below the servo tester control knob is set to full left (minimum).  Sure enough, the pulse width as measured by the scope is 915uSec.  That's pretty darn close to the 1mSec width in the drawing above.

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With the knob set to full right (maximum) the scope cursors show a pulse width of 2.14mSec; pretty close to the ideal 2mSec in the drawing.

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Using the MSO5104B oscilloscope to zoom out on the signal we can see that the pulses repeat steadily every 20mSec.  If you check the tutorial at Jameco you will know that is exactly what is expected.

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Conclusion:  Splurge the $1.50 USD and treat yourself to this handy device.  It really helps to verify that a servo is actually working and in setting the movement limits on your project.  Below are two short videos of the servo tester in action.

 

 

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Here a short video where I use a Tektronix AFG3252C to send the control pulses to the servo.  The AFG3252C has infinitely more flexibility, but cost a few dollars more than the eBay option.

 

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Thanks for stopping by.  Build something.

PVC Pipe Based CNC Mill using Arduino

What hobbyist doesn't want a CNC machine?  But realistically, how many can really justify the need for one?  Not me, but we did want to learn about CNC machines and experiment with GCODE.  If you are wanting to do the same; keep reading...

We had an Arduino UNO sitting around doing nothing as well as some stepper motors we rescued out of an old laser jet printer.  That's a good start for the project, but some hardware/software to drive and control those stepper motors was still needed.  Oh, and some PVC pipe and connecting joints to construct a mill platform, don't forget that.

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After a bit of searching we decided to use the Protoneer CNC Shield for Arduino.  You can get this shield for about $20US.  It comes completely unassembled, but a soldering iron and an hour or so of time fixes that.

Before assembly it looks like a bag of parts.  After assembly it looks like this:

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The Protoneer CNC Shield plugs right into the Arduino UNO just like any other shield.  Of course, after you get it assembled you will want to test it.  But wait, first you will need some software to communicate with the Arduino and drive the Protoneer CNC Shield.  

The Protoneer CNC Shield is 100% GRBL compatible.  This is great because it provides you with several software options for CNC control.  I wanted something that was 1) free and 2) could be used with Windows or LINUX.  I experimented with SketchUp, f-engrave, and GCODESENDER.  In the end, I seemed to prefer GCODESENDER the best.  YMMV.

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Here is my first test run controlling the X and Y axis steppers.  Ahhhh, the sweet sound of progress:

Then added the Z axis:

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Before constructing the PVC "mill" I tested the rig on a Etch-a-Sketch.  Seems to work well enough to continue.

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Next, thanks to Home Depot and their endless assortment of PVC accessories, the rig below was constructed.  I did not use any PVC glue and the slide rails for the milling tray were held on with P-clamps and larger diameter PVC 'sleeves' for bushing/linear bearing.  

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Here are a few first run tests of the rig in motion:

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Example of simple text:

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A bit more elaborate example:

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The rig works.  Could you create an elaborate 3D design with it?  Heck no, but that wasn't the point.  It was; however, a great learning experience.  With some effort, anyone could take this concept and improve it to something more useful if they desired.  If you choose to take that path, drop us a line to let us know how it turned out.  Thanks!

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