Archive for May, 2014

Servo Jitter Solved

Friday, May 30th, 2014

My MG-995 servos were jittering with my “The Better Mousetrap Servo Tester”, and today I decided to get the bottom of it before I started testing HexPi, my RoboPi + Raspberry Pi based hexapod robot.

When I hooked up a scope, and looked at the 1500us centering pulse and the servo power, here is what I found:

The Better Mousetrap Servo Tester @

Time for some troubleshooting…

You can read the rest in the “The Better Mousetrap Servo Tester” build log at

(thanks to ecompservices for pointing out the link above was broken!)

Ultrasonic Servo?

Thursday, May 29th, 2014

I am currently adding support for ultrasonic range sensors to the RoboPi firmware (Parallax Ping, SeeedStudio and HC-SR04), and it is going quite well!

Yesterday I had a bit of fun controlling a servo position based on the distance reading from an inexpensive HC-SR04 sensor! Move my hand closer or away and the servo turns left to right, and centers if my hand is too far away.

The servo was more jittery than I’d like, so I am investigating weather it is a timing issue, or an issue with the inexpensive Tower MG-995 servos I am currently using. Time to pull out a scope or logic analyzer!


In case you are curious about the PropPlug in the photo, I develop the RoboPi Linux libraries under Ubuntu on a beefy development box, and re-compile (and re-test) on a Raspberry Pi before release.

For more, please see:

“The Better Mousetrap Servo Tester”

“HexPi – Hexapd Pi Robot”


The Better Mousetrap

Wednesday, May 28th, 2014

I added two breadboards to TBMST, this allowed me to clean up the power supply wiring, and will let me start wiggling HexPi’s legs!

The Better Mousetrap Servo Tester

For more (and larger) photos, please see “The Better Mousetrap Servo Tester” build log.

Advanced Servo Tester

Tuesday, May 27th, 2014

Now that all the legs on HexPi are mounted and calibrated, I’ll have to start figuring out gaits and the best way to use all those legs.

It seems to me that it might be useful to have some “string puppet” like control of HexPi, so its time to brush off my “The Better Mousetrap” servo tester from my HexPi build log.

As a matter of fact, I’ve decided to make a separate page for it, as it is a significant project in its own right…

Here is the link for the new “The Better Mousetrap Servo Tester” page:

HexPi’s legs

Monday, May 26th, 2014

I’ve finished calibrating HexPi’s legs, and even labeled all the servo leads!

More at: