I am running the APM 2.6 autopilot on my hexacopter. That system uses a sonar sensor to accurately measure altitude when flying close to the ground. Mounting the sensor is somewhat critical. It must have a clear view of the ground, be mounted away from any electrical wires which may cause interference, be clear of any mechanical interference from the props, and be isolated from vibration.
|MaxBotix MB1240 Ultrasonic Rangefinder|
The QUADframe that I am using does not come with a mount specifically for this sensor so I had to make my own. I decided to mount the sensor on one of the landing legs. I started by cutting a piece of aluminum angle to length. I drilled two mounting holes in the mount and legs. Then I scribed the contour of the leg into the aluminum. I shaped the end of the mount on my belt sander to match the curve of the landing leg.
|sensor in mount|
Next, I drilled the holes for the sensor. I attached the sensor to the mount with nylon screws and standoffs to prevent shorts. After that I added the wiring. MaxBotix recommends making a power filter to eliminate electrical noise. You simply add a 10 ohm resistor and 100 micro farad capacitor to the power supply lines.
|power filter circuit|
|sensor wired up|
I attached the senor to the APM according the the diagram below.
I added a piece of Kyosho Zeal between the mount and the landing leg to cut down on the vibration transferred to the sensor. As a final measure, I wrapped the entire sensor in foam to cut down on acoustic interference. The sensor appears to work pretty well. It gives accurate readings when the hexacopter is static. During flight the readings seem to get a bit erratic. I may just need to adjust the sonar gain in the Mission Planner software.
|ready to fly|