Long-Line Sensor Payload Demonstration


Today I did something a little bit unusual, and definitely more difficult than flying around with a camera. A possible commercial customer asked to see a demonstration of a helicopter flying with a 2.5kg sensor.  This sort of thing is commonly done for magnetometer surveys for mining exploration.  The sensitive sensor must be hung from a long line in order to get it away from the magnetic interference from the UAV.  This could also be done for water or gas sampling.

The big helicopter has no problem with flight control despite the hanging weight.  It just requires some special piloting to control the swinging, basic pendulum dynamics.

These sorts of surveys require many tight passes at low speed, so it takes a long time to cover a large area.  It's an ideal job for a gas powered helicopter UAV.  This one can fly for an hour easily.

It would be possible to create a payload management system which would measure the position of the sensor via the angle of the rope, and automatically control the UAV to control the swinging (basically, the reverse of a balance bot).  Something I would love to work on in the future.

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Comment by John Bond on March 19, 2016 at 9:21pm

The first thing I thought of on seeing this is some pics I have of manned helis carrying these type of sensors.  They are on an older PC which I don't have assess to right now.  But, this is pretty much an ideal use of a gas RC heli as vibrations on the chopper don't really matter.  While I suppose you could position it based on the heli's position and an estimate of the line angle there's no reason why a complete positioning system can't be on the sensor.  An IMU and L1 GNSS sensor will easily yield cm level positioning compared to the heli and perhaps in absolute mode depending on the distances involved.  I don't think these passive systems would hurt the sensor significantly ... or would they?

For those of us who are just vaguely familiar with the concept is a 2.5 kg sensor "good enough" compared to some of the larger sensors carried by manned choppers?  I'd roughly estimate what I've seen at closer to 25 kg hanging below Bell 206s and similar.

Comment by Ravi on March 19, 2016 at 9:40pm

you keep doing amazing things. you are a great treasure for this blog. keep it up!

Comment by Rob_Lefebvre on March 20, 2016 at 5:00am

I should point out that this helicopter is running internal rotor speed governor control.  That's why the rotor speed is so constant.  I started working on it several months ago, and it's almost ready for inclusion into Master, but I've been too busy trying to find funding to keep working on it.  Hopefully it could still make AC3.4, but I don't know.


@James, I have actually thought that it would be fun to try something... well this is a big radical but... imagine a winch motor on the helicopter.  And at the bottom of the line you have a small quadcopter upside-down. It would be tensioning the line, and also controlling the swing.  Then put a claw on the bottom of the quadcopter. Could be a way to pick up or move objects on the ground.  Like a moving, soft robotic arm.

@John, yep, perfect job for a gas helicopter.  I don't actually know a lot about the actual sensor itself, if adding more electronics would cause a problem or not. It's probably possible. I think 2.5kg is a standard weight for these sensors these days.  I've spoken with others and it's similar to what they are using.  This heli could probably lift a 5kg sensor with no problem at all.  Other than the swing, it doesn't notice the weight at all.  And the swinging can be controlled, just need a bit more practice, this was like my 3rd flight.


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Comment by John Arne Birkeland on March 20, 2016 at 5:51am

Attach the line to a 'joystick' hanging up side down to get angular data for the payload.

Having a weather wane/rudder surface on the payload will probably also help in forward flight.

Comment by Rob_Lefebvre on March 20, 2016 at 7:38am

@John, yeah that's a good idea to use a joystick gimbal.  I'd only be concerned finding one that can take this weight.

@Guy, unfortunately I can't show too much, as it is commercially sensitive.  At this point my best chance at being able to earn a living and continue developing Arducopter, is to sell these systems, so that's what I'm working on.  Unfortunately, that effort has stopped me developing the code further.  That's the reality of the situation.

This was done as a prospective thing for a company interested in the concept.  It needs further development, but it's definitely possible.

Comment by George Kelly on March 20, 2016 at 10:41am

Cool.

I've been playing around with slung payloads a bit.

At first, I thought 'ropes only' for weight savings (I'm using some Dyneema kite line).

But I've gravitated toward lines taking the weight of the payload, but a more rigid pole between the drone and payload to control payload twisting and swaying. By not having to take the payload weight, the pole can be lighter.

Telescoping tube, or fixed pole 'folded' out to the side on take-off or landing, or a combination.

Of course, at the distance of your payload below the chopper, probably not practical.

Have you confirmed how far below the chopper that sensor needs to be to avoid interference? (The farther below, the greater the control problems, I'd assume).

I'm also worried about slack in the lines during landing being blown up into the props - but more a concern on an X8 than a heli. They may have to be weighted down (ie fishing weights or such).

Anyway, good luck (my target application is also mining-related. Could be a 'Canadian' thing :)

George

Comment by Rob_Lefebvre on March 20, 2016 at 11:06am

Hi George,

You really should be considering gas powered helicopters for any kind of application like this.  The advantages are huge.  Pour gas, pull cord, fly for an hour, land, pour gas... all day long.

Comment by Gary McCray on March 20, 2016 at 11:28am

Hi Rob,

I am familiar with nuclear precession magnetometers being towed behind light airplanes and under helicopters for this kind of work.

It is my understanding that these are the only ones suitable for this kind of use.

I didn't think that they were available so light as 2.5KG, but on looking further I found one at 760 grams:

http://www.rhdc.co.uk/docs/PPMG2A_Report.pdf

So it looks like even a one kilo tethered payload could be really valuable and boy have those things come down in price - $2600.00.

A really great use of a heli UAV, hope you can get somewhere with it.

Just a small suggestion, the real helis (and most airplanes for that matter) normally use a winch to only lower the magnetometer during actual use and then retrieve it before landing, seems like a simple solution to me.

Best Regards,

Gary

Comment by Rob_Lefebvre on March 20, 2016 at 11:42am

Yeah, I've actually got a sail winch servo I've had in a drawer for a while now.  It's definitely a potential solution. Though I think that wouldn't work in this case, the rope would need a larger drum than what it's equipped with. But, definitely possible.  The helicopter can take more load easily.  I know somebody flying essentially the same helicopter with an 11kg payload.

Anyway, this was just a quick KISS test to show it can be done.

Comment by Marcus Wright on March 21, 2016 at 10:14am

Hey Rob, Good work.  If I had money I'd invest in your venture!!!!  Have you played with head speed any?  Do you think it's worth even considering?

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