Thursday, January 10, 2008

Fly as you train, train as you fly.

I've been flying RC airplanes for a very long time, but I did not ever fly a helicopter until about two years ago. I bought the real flight simulator and made a serious, 15 minutes an evening , effort to learn to fly the helicopter. I did this every evening for months. I did not buy a helicopter until I could fly the simulator with full realism and gusty wind 10 times out of ten for A full tank of gas without crashing. Once I could do 10 of 10 I bought a helicopter jkit and started trying to fly in the real world. This illustrates a subtle point the picture below shows me sitting in my computer chair flying the sim.
The only problem is that if you then take a picture of me holding the real transmitter
like I fly the real helicopter there are differences.

With the transmitter on my lap I hold the sticks with my fingers, standing with the tranmitter dangling I naturally fly with my thumbs. On the simulator I can easily do 720 degree piroettes
without out gaining or loosing altitude ot position stability. I real life this is not so easy.
So I've started practicing with the simulator standing in front of the computer with the simulator controller hanging from a strap. Even subtle differences between things make a difference. Especially if it is in trained muscle memory.

The next helicopter Step.

Basic control laws are going to be:
1)Desired course/way points ->generates desired position.
2)Current position(gps) and desired position ->Generate desired velocity.
3)Desired velocity +Actual velocity(gps) ->Generate desired pitch/roll attitude.
4)Desired Pitch Roll Attitude +Actual pitch roll attitude(imu) -> Generate (virtual) Elevator and Aileron signals.

Separately we control heading (alwayas points true north) and altitude. (Heading control is done and works)

Note that all of thsi software will be identical on the rocket, except the very last part
>>>Desired Pitch Roll Attitude +Actual pitch roll attitude -> Generate Elevator and Aileron signals.

I've had all this working with the helicopter simulator for 6 or more months. I'm just a bit cautious and chicken when it comes to flying it in the real helicopter. I'm going to work my way up the list backwards. This brings me to todays waffling decision. As presently set up the helicopter is about 4K of hardware and 100 hours of work. I'm a bit cautious with it.
I worked out the yaw control with a lazy Susan. Today I gathered all the parts necessary to
build a mount for the helicopter that would allow it to move about 15 degrees
in pitch and roll and 360 degrees in yaw freely. It would take me about 4 hours to assemble all of this. This only helps with Step 4 all the other steps have to be done in free flight anyway, so is it worth building the pivot mount??? My strategy is as follows Beyond the basic flight controls I have the software set up to respond to two of the RC transmitter controls (outlined in red below)

Aux 2 is a three position switch that selects three software modes. 0,1,2
Mode 0 is full manual control.
Mode 1 enables the autopilot parts that presently work. (currently only the yaw)
Mode 2 enables the new component we want to test.

"Lever" is a slide lever on the side of the helicopter that I have setup to control a software
variable that goes from 0 to 100. The intent is to have this lever control the gain of the control loop I'm currently working on. The problem is that both of these are on the wrong side of the transmitter for the next step as the cyclic control is what I'm trying to automate and also the right hand stick. My real problem is that I actually need to start flying the helicopter regularly.
I also do most of my work in the evening so I need to fly it at night and its not safe to fly by myself. (The big Trex600 could cause serious injury if it went out of control and went for the pilot) I've flown the vehicle a couple of times in the dirt parking lot near the DelMar fairgrounds
(The security guard thought the helicopter was cool, but told me that if anyone asks I'm not supposed to be there.) I could start flying at one of the regular RC model flying clubs, but the fact that the system has a GPS and could, with the proper software, fly beyond the pilots direct line of sight makes in in violation of the RC club safety rules. I think it would be rude to jeopardize a long standing RC club and its flying field by violating the rules.

1 comment:

Dam said...

Interesting post, as usual. Thank you for sharing this with us !