Recently upgraded my DX6i to a DX8. In doing so I found out (remembered actually) that I only had 6 channel PWM receivers in my APM 2.6 copters. DOH! Really didn't want to have to get two 8 channel receiver$ to use the extra channels. Started thinking how nice it would be to use PPM single wire input like serial RX on all my *flight controllers. Quick google search and BINGO! http://www.lemon-rx.com/index.php?route=product/product&path=70&product_id=138 This frees up two six channel PWM receivers for my planker builds AND simplifies my APM configs at the same time. Thought it would be an easy swap out. HAHAHAHAHAHAHA. It was a good learning experience and a bit more time consuming than first thought.
The easy parts come first. Remove old receiver and all but the channel 1 three wire connector from APM. Plug channel 1 cable from the APM into top pins of the LM0039. Plug bind plug in to lower pins of LM0039. Put a pin jumper between theignal pins for channels 2+3 on the APM. Turn it on and bind your receiver. After binding, you can set radio failsafe by setting the radio channels where you want and press the button on the LM0039. Turn it all off and remove the bind plug.
Now for the fun! The default mapping for PPM channels 1-3 is different than the default for Spektrum. if you do not have the abillity to remap channels in your TX, you will need to remap the first three channels in the APM . (My DX8 can not remap the first 4 channels) I also found out the hard way, that different versions of Arducopter can have different PPM channel mapping and may or may not work correctly with PPM input. 3.2 works fine on both my copters. 3.1.2 looked like it would work on the radio page, but I could not get it to arm no matter what I tried. The parameters you will need to adjust for the channel mapping from Mission Planner are:
RCMAP_PITCH,1
RCMAP_ROLL,3
RCMAP_THROTTLE,2
You may or may not need to adjust the channel numbers depending on your hardware and firmware levels.
After mapping, redo the radio calibration in Mission Planner. Here's the next gotcha. Mission Planner does not take into account that you remapped channels and does not set the center position correctly on the throttle and whatever channel it was mapped from. You will manually need to check and adjust the following parameters:
RC1_TRIM,1501
RC2_TRIM,1001
RC3_TRIM,1502
Note that the Throttle trim is usually set at 0 throttle and in this case is 1001. My throttle channel above is 2 and in my case, I have adjusted the trims on Throttle and Roll to their correct values. If you skip the Trim step, the copter will try to flip immediately on take off unless you provide full left roll... (because 1001 for roll would mean the center is full left)
There is some other channel range setting and sub trim config on the DX8 I had to do to get full range and center close to 1500. That is the typical config that would have to be done with any setup so I am leaving that out in this post.
Hope this helps somebody!
Cheers!
LitterBug
The easy parts come first. Remove old receiver and all but the channel 1 three wire connector from APM. Plug channel 1 cable from the APM into top pins of the LM0039. Plug bind plug in to lower pins of LM0039. Put a pin jumper between the
Now for the fun! The default mapping for PPM channels 1-3 is different than the default for Spektrum. if you do not have the abillity to remap channels in your TX, you will need to remap the first three channels in the APM . (My DX8 can not remap the first 4 channels) I also found out the hard way, that different versions of Arducopter can have different PPM channel mapping and may or may not work correctly with PPM input. 3.2 works fine on both my copters. 3.1.2 looked like it would work on the radio page, but I could not get it to arm no matter what I tried. The parameters you will need to adjust for the channel mapping from Mission Planner are:
RCMAP_PITCH,1
RCMAP_ROLL,3
RCMAP_THROTTLE,2
You may or may not need to adjust the channel numbers depending on your hardware and firmware levels.
After mapping, redo the radio calibration in Mission Planner. Here's the next gotcha. Mission Planner does not take into account that you remapped channels and does not set the center position correctly on the throttle and whatever channel it was mapped from. You will manually need to check and adjust the following parameters:
RC1_TRIM,1501
RC2_TRIM,1001
RC3_TRIM,1502
Note that the Throttle trim is usually set at 0 throttle and in this case is 1001. My throttle channel above is 2 and in my case, I have adjusted the trims on Throttle and Roll to their correct values. If you skip the Trim step, the copter will try to flip immediately on take off unless you provide full left roll... (because 1001 for roll would mean the center is full left)
There is some other channel range setting and sub trim config on the DX8 I had to do to get full range and center close to 1500. That is the typical config that would have to be done with any setup so I am leaving that out in this post.
Hope this helps somebody!
Cheers!
LitterBug
