Pin point hover?

[robe_uk]

Hi Guys
I am not looking to do anything to fancy, just have a helicopter hover in the place I leave it.

I intend to use the heli as a camera ship for digital still so I would like to fly the heli up to what ever position I want and have it sit there stable hands off while pictures are taken
The heli doesnt need to fly position to position itself just hover.

I know it would be easy to manually fly it and hold its hover, but thats no fun ;)

So I guess I need to know what to use.

Keep level => Co-pilot ..... what about wing drift... what about gyros
Keep still => some sort of movement detection.
Keep height => height detection

Have all tie together,
If heli has to sit nose down a bit into wind getting info from movement detection to stay still, what will happen with the co-pilot fighting to lift nose to get level etc.

Am sure the are loads of questions I have not thought about.

Has this been done before (am sure it has)

Any help welcome.

This is a long term project on the cheap....am mean with cash lol

[Mr.RC-CAM]

You are asking a very tall order. If an off-the-shelf solution is needed, then about as close as you will probably get is offered by www.carvec.co.uk. It is not "cheap" but the price is fair.

[crux12]

You are asking a very tall order.

Agreed, In fact this currently seems to be more difficult than forward flight. GPS is not going to be an option or any sensor with drift.

[pmackenzie]

Agreed, In fact this currently seems to be more difficult than forward flight. GPS is not going to be an option or any sensor with drift.
Why not GPS? Differential GPS can be accurate to a few centimeters:
http://www.esri.com/news/arcuser/0103/differential1of2.html
Pat Mackenzie

[Mr.RC-CAM]

Why not GPS? Differential GPS can be accurate to a few centimetersIt would be useful. However, I wouldn't expect a GPS to readily determine minor pitch or roll attitude changes on small bodied aircraft like an R/C heli. I think part of the application was to stay quite level, which would need additional sensors or some serious GPS magic.

[kd7ost]

Agreed. It would take quite a pile of parts working together. A co-pilot can be used for pitch and roll. I don't know if the CCCP version of the co-pilot ever came about though so you might have to avoid that in the Helo.

Position information from a GPS can't tell you which direction it's drifting off your hover point unless it's moving enough to know which direction it's moving. If it's moving enough that a GPS can tell what direction it's heading reliably, It will be moving by feet at least and most likely meters. The system also has to know what direction the Helo is heading or pointing. If you're facing north, and drifting east, the unit has to know to correct left. If it's pointing South and drifting east, it has to know to move to it's right. This needs to be done in a 360 degree arc. Wow. You need a high resolution electronic compass as a way to know which direction you're heading. The GPS is still a pretty course instrument for that. WAAS enabling will generally get you to within a few meters not centimeters.

This doesn't even account for yaw but you might get by for a little while if your using a real good heading lock gyro. With the compass on board though you can lock in a heading with a gyro and keep correcting to that as drift occurs.

Keeping it in place and not drifting hands off for any length of time will be a chore. MrRCCam is right about the carvek unit. That's pretty much what it will take. There's a lot to it. A GPS won't do very much of the task by itself.

Dan

[ehx]

If you can hover "hands off" that's 85% of complete autonomous flight. Simple concept in theory, not so simple to actually do.

CARVEC does it, and does it fairly well. It's not cheap though. CARVEC uses inertial sensors for attitude, autonomous GPS for position (to hold it in one place to a few meters), barometric data for smoother altitude then autonomous GPS alone, and a magnetic compass for direction. Under $2K in hardware costs and a "poor man's" implementation could probably get it to under $1K by using IR sensors for attitude with some reduction in performance. Now add the control loops. Easier said than done. Make some return on your investment and you can see why a CARVEC system will run near $10K.

GPS alone CAN do everything. In fact it can be a superior system, but it will cost more. The hardware could cost as little as ~$3K. This would include 4 10Hz L1 carrier phase GPS boards, a radio modem pair to transmit carrier phase corrections, and a PC104, or similar format computer to process the data. In addition to adding the control loops for flight you would need to add real-time carrier phase ambiguity resolution software. Write your own (not easy) or buy a package for ~$5K.

There's A LOT of support programming required for any hardware method, but with GPS you now have a 10Hz position (X,Y,Z) good to a couple cm and roll and pitch to ~ 0.25 degrees and yaw to ~0.1 degree (both values dependent on antenna separation, but easily achieved with less than a 1 meter separation). Latency will be a little more than 0.1 second. Not ideal, but fast enough.

Disclaimer: Actually doing this is harder, much harder, than you think. If you try it you may find that spending a bit of money to solve at least part of the problem starts to look like a good idea.

[robe_uk]

Hi Guys
Thanks for the information you have all provided, been a real eye opener :eek:
Funny how things seem simple to the casual observer but when we go looking it is never that.
Might try just hovering myself and have someone esle control a stablised camera mount.

(oh I pulled my first loop with my sceadu 50 heli today, just saying cause am still smiling :D )

[mckaneorg]

I have often wondered if having 3 heading hold gyro's would do the trick? You would have to put it into position.

I have tried the co-pilot but the problem is when I use it on my bigger heli. I get allot of glitching. Right now I am using the JR PCM radio and I wish I could get that FMA reciever to stop glitching.

-j

[reedchristiansen]

A few questions for you guys who have done it:

1. Is an EKF outputing earth fixed velocities (x,y,z) necessary, or is the velocity information from a 4 hz GPS such as the microblox sufficient to hold a 2-d (position only ) hover?

2. This relates to the first question: Is it important to integrate accelerometer information into the velocity information from the GPS to get acceptable results in a hover (3 meter hover)?

3. How hard is it to control altitude? Is baro sufficient or do I need to combine baro with z velocity and acceleretion information? I assume a laser range finder is important for any hover close to the ground?

4. Has anyone done this with useing a height above ground sensor?


Thanks for you insight - this thread has opened my eyes also. One of my tasks for next year is to adopt the Procerus Kestrel autopilot for helicopter use.

Reed