Servo - September 2016

issue. This only took about 15 minutes and I was back in business.

First, connect the ground side radio to the computer. After any necessary drivers install (I tested this on both my Mac and a SurfacePro running Windows 10), the OP-Link icon becomes active. Click this icon and read over the options to configure the radio. The main thing we need here is the device ID to tell the flight controller. Write this number down.

We also have to tell the ground side radio that it will coordinate communications by clicking the “Coordinator” checkbox. Set the maximum output power of the radio to 100 and set the min/max channel settings to match your country’s band plan. In the US, we can leave these settings as 0 and 250, respectively (Figure 8). Save the settings to the setup and disconnect the ground side radio.

Next, connect the air side radio (the flight controller) to the computer. Again, when the OP-Link icon becomes active, click it to enter the radio settings. This time, we make sure that Coordinator is not checked. Enter the ground side radio’s device ID into the coordinator text box. Again, set the max power to 100 and the min/max channel settings to meet with your country’s regulatory standards.

Now comes the fun part: testing it out! Disconnect the flight controller and reconnect the ground side radio. I placed my quad back out on the patio and powered it from the flight battery. This time, the long USB cable is not necessary. In a few moments, the radios will bind and you should see the RX indicator on the LibrePilot GCS go very high, as well as see the binding in the OP-Link panel. Returning to the control panel, you should see the indicators update if you change the orientation of the quad. We now have wireless telemetry!

I zip tied the antenna to the GPS mast to keep it out of the way (Figure 9). Another excellent solution would be to design a part to be 3D printed. We may do that in the future, but for now I don’t know exactly where the antenna is best placed and I want to be able to easily swap out the entire flight control system to be able to test other products.

I did a few flights to test the telemetry link. I found that the range was not very good. It seemed that if the aircraft was more than about 30 feet away, it would not maintain a reliable telemetry stream. Some ground testing confirmed this. It looks like I have one of two issues: 1) a second damaged radio; or 2) a flight controller or receiver with non-genuine and poor performing parts. It is hard to know which is which now, but many OP-Link users have videos of telemetry working at ranges of many hundreds of meters. I’m going to be on the LibrePilot forums and try to figure out exactly why my system seems to have a limited range, and try a different set of transmitting hardware.

GPS Stabilized Modes

With a GPS onboard, we have nine new flight modes to explore ( https://librepilot.atlassian. net/wiki/ display/LPDOC/GPS+ Flight+modes). The most interesting of these to me are position hold mode, return to base, and path planner modes. Position hold mode keeps the quad in place regardless of the winds and environment (within reason). Return to base mode will cause the quad to fly back to its home location and hover. The path planner mode allows the quad to autonomously fly a predefined flight path.

To use the GPS modes, we need to change the way the quad calculates its attitude (orientation and position in space) and set up the flight mode switch on our transmitter and flight controller. First, connect your flight controller or ground side radio to the computer. In the configuration tab of the GCS, click on the Attitude settings on the left side of the screen. In the settings tab, there is a drop-down menu labeled “Attitude Estimation Algorithm.” We have been using the “Basic (Complimentary)” estimation algorithm, but need to change this to “GPS Navigation (INS13).” Once that is done, save the settings.

Next, we need to set up the flight mode switch on our handheld transmitter to control how the quad will fly. We did not set this up when we first went through the transmitter configuration wizard. To do this, we need to set a “Pitch Curve.” This is a non-intuitive process, so you can follow along with the text and a helpful You Tube video I found as well ( https://youtu.be/6n_5wNA2j TI).

Press the menu button on the handheld transmitter and go into the settings page. Go down to the “PIT/CV” item and select it. By default, the pitch curve has a linear relation to the throttle control for all three positions of the flight mode switch. With the flight mode switch in the top (normal) position, set all five numbers on the curve to 0%. Next, move the flight controller switch to the middle position (ID1) and set all of the values to ~50%. Finally,