After reading several blog posts and discussions about folk having startup issues with ESCs, APM2s, etc, I thought it prudent to build a simple servo tester to allow ESC checks sans APM functionality. The new issue of Make Magazine, #31 (I did a discussion post last week after the mailman delivered it) has a section on servos and their function. It included a common manual servo tester/driver.
I had everything needed to build it in my stash except a 50K pot that was less than 10 turns. A quick trip to ebay and $5 later got me 5 pots.. delivered in less than 5 days!
Why, you say, didn't I just buy a premade servo tester while I was on ebay? In general I like building things rather than consuming things. If you started with my first blog posts, you may recall that I buy where it makes sense and build when it pleases me and I have the parts on hand.
In the case of my tester, I know and understand how it works. I didn't take pictures of the scope outputs because the circuit is so well known and there are much better sites that can show you servo drive theory. Go consume them for details. ;-)
How, pray tell, did I determine the CCW, CW direction of the motors without installing the props? I ran the motor at the lowest speed adjustable with tape on the outrunner section of the motor. My finger served as the direction indicator.
Motor 1 was fine CCW. All the others required a lead swap to obtain correct rotation. This process also allowed me to run each motor up to the max my simple tester provided. Listening for bearing knock, grind or other mechanical issues that might have crept into the build was also part of the process.
One thing that is for sure, we need some type of kill switch on these machines. I haven't put much thought into it but it would be a grand safety feature for these birds.
Next up I wanted to verify the output power of the ESC to the APM2. The simple tester worked so I knew it was in the range for the circuit design but the APM2 is a little more particular than a 555 circuit. On a previous trip to the local hobby shop an Electrifly Power Match power meter had followed me home.
The power meter has Rx/Tx inputs to act as a voltmeter for those supplies, perfect for what I wanted to know. The ESC may not have an adjustable output (like Castle Creastion units) but the 6 millivolt low value should not be a problem if the ESC holds steady.
The Arducopter assembly manual, if read sequentially, led me to believe that the power to the APM2 did not require the JP1 jumper. It would not power up as shown in the assembly manual. Further reading indicated that JP1 is the default mode. I tested the APM2 with a USB cable and it powered fine. Back to the PDB lead, JP1 installed and...
hurrah! Going for the gold I added the Spektrum power input. The receiver modules lit up looking for a bind (not shown in the above pic). The Tx was in the house so I declared victory and called it a day.
Little steps add up and now the ESCs are direction correct and I can begin to integrate the APM2 software and bind the Spektrum Rxs with the Tx.