Electronic co-pilot--how to calibrate

[jrohland]

While I am not currently building an AP ship, I do want to play around with electronic stabilization.

To that end, I purchased a FMA Direct CPD4 (http://www.fmadirect.com/detail.htm?item=1489&section=20). Since my heli is a Miniature Aircraft Razor 600E (http://www.miniatureaircraftusa.com/helicopterkits/1027_razor_600e/1027_kit_main.asp), which uses a CCPM configuration, I needed to add on a Helitronix Multi-Mixer (http://www.helitronix.com/page11.html). Everything is installed, configured and test flown.

I have not been able to test fly it over a large field but, so far it looks like the heli wants to go aft and port whenever I switch the co-pilot on. Anyone have any idea how I can calibrate the device to have the heli stay in place?

Also, I have the option to put pitch and roll gyros onboard. Should I?

Is this plan flawed? I.E., should I just give up and put an AP-2000i (http://www.spartan-rc.com/products/ap2000i/ap2000i.htm) on?

jrohland

[MarkWebber]

I've never flown a copilot version but I thought they had a calibration feature...no? If not, you may try tipping the sensor to the rear and left to neutralize the drifting tendancy.

[jrohland]

Yes, the CPD4 does have a calibration process. I followed the instructions. I just wondered if anyone had discovered any "tricks" to improve the outcome.

jrohland

[crewchief]

Hi jrohland,

You're probably 90% of the way there - remember the 90/10 rule? I've flown the DraganFlyer quad heli with "Thermal Intelligence", have used the CPD4 on the Falcon 3D, and am now using the AP-2000i on the T-Rex 600, so I've got a pretty good feel for how they work.

The behavior you described when any of these devices is activated is common. First thing you have to do is see if it corrects for the behavior itself. The AP-2000i comes "calibrated" from the factory, and I have not re-calibrated it. However, when I first started using it, when I switched it on at about 50', it would jump backwards and I would have to give it full stick to correct. The AP-2000i appears to have a more sophisticated internal self-leveling algorithm. I decided to hold off on re-calibrating it, and it turns out I have not needed to. However, I sometimes have to hold some major correction for a few seconds, then it seems to level out with the stick centered. Also on the AP-2000i I use 50% authority, while on the CPD4 I set about 80% authority.

So the first thing you need to do is figure out if the imbalance is internal or external. There are two parts to the CPD4 calibration - setting the differential gain and setting the horizon level. Usually it's the leveling that causes the problems. You don't need to calibrate the CPD4 every flight, like the DraganFlyer, but you DO need to calibrate and level it at least once. When you set the gain, always pick the coolest spot you can find, like over green grass. This allows variations of ground temperature vs. constant sky temperature to work in your favor. If you calibrate over hot asphalt, then fly over a grassy field, the controller will not recognize the ground because it thinks it should be a lot warmer than that, and it will not be able to maintain stability.

Level the heli in the middle of a large open field or parking lot. You can set the gain by letting it see the earth/sky differential over grass, then set the level out to the middle of a large field or parking lot. The leveling process is looking for deltas between the sensors - it doesn't care what the absolute temperatures of the sensor readings are, it is just looking for differences in temperature to determine what level should be. Thus if the sensor pack is crooked, it will compensate for that. The thing to remember is you don't want it to "see" any warm vertical objects anywhere near it when you set the level.

Calibrate the heli under typical weather conditions and put it into about a 40' hover with the stabilizer on. If the heli wants to move aft/port (SW), correct for that movement by holding the stick in the NE position. Now slowly rotate the heli 180 degrees. Any change in the stick position to hold the hover? If you've set the level correctly, it should require a SW stick position to hold the hover. The sensors are picking up a heat source somewhere and reacting to it. The source of heat is not always obvious.

I would suggest going through an accurate gain/level calibration once a season, then leave it. It's hard to find the ideal place to set level, and it's better to leave it alone after that, even with changes in the weather. Unless of course you make a sudden move from, say Bogota to Reykjavik...

[jrohland]

Bruce,

Thanks, your post is a great help.

One other thing. When I did the initial setup (the one with the red button held down while applying power) I shut off the auto-trim feature. Do you recall if you used auto-trim or not? I assumed auto-trim is more for planes. Either way, I am advanced enough that I believed the auto-trim should be off as the manual says that is the setting for advanced fliers.

Thanks again,
John

[crewchief]

You should leave the auto-trim function activated if you plan to turn off the CPD4 before you land. This will make the transition smoother by not changing the trim when you switch.