Most of the parts have arrived so I've been able to get accurate measurements and start on the airframe, a small tricopter. Materials are carbon tubes & 3D printed PLA.

The laws here in Chile are restrictive. You need a license, drone registration, insurance and the drone has to pass inspection - apparently *very* hard to get.

If the drone weighs less than 700 grams its classed as a toy, which means no restrictions other than common sense and being responsible for any damage. So that's the plan - a 'PichiCopter', as 'pichi' means 'small' in Mapudungun.

Here's a screenshot from CAD, lots to do yet but with luck I'll start building at the weekend.

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Comment by JeanLeFlambeur on April 20, 2017 at 2:12am

I like your yaw system. I guess you went for a tri to save weight, right? You might end up with more weight than if you went for a X quad because of the servo (which alone is 20-30% of the weight of an extra motor), the yaw linkages, extra CF tubing etc. I also went down this road to save weight and in the end I ended up with a tri of comparable weight to my quad, but less total thrust (due to a missing motor). 

Comment by Bob Morley on April 20, 2017 at 4:49am
Its all experimemtal, wouldn't be fun if it wasn't :-)

The motors weigh 55g each, I'm trying very small metal gear servo that weighs 13g, the tail boom bearings weigh 3.5g each and one less esc than a quad. Should be a net saving.

Hoping an ESC can provide enough to run the Pi2/Arduino, if yes I can lose the UBEC and save some more.
Comment by Marc Dornan on April 20, 2017 at 7:00am

Great stuff! I do agree with Jean though -- a tri generally just adds complexity and mechanical unreliability for questionable weight savings. But your design will be easy to adapt to a quad if you need to change it. Please post your progress though. I often use these instead of off-the-shelf BECs. Very little weight penalty.

Comment by Gary McCray on April 20, 2017 at 10:48am

Hi Bob,

I greatly approve of making a copter that can fit in the underweight class, I think that is going to be a huge market in the future.
It was basically put in so they didn't have to try and deal with toys, but advances have been so fast that fully gimbaled high resolution cameras are going to be able to fit on copters in that class real soon now.

Aside from the regulatory issues, the small size and lower weight also hugely reduce the real liability and perception of danger associated with bigger copters as well as making them generally less obtrusive.

there is a huge pay off for being able to do this.

I do however also have to agree with Marc, a quadcopter is a more reliable and more maneuverable and simpler solution.

You do have an unusual and elegant tricopter servo solution, but frankly quadcopters are better in every way and much more maneuverable.

I any case I wish you great luck and will be watching your progress.

Right now in the commercial area DJI is clearly headed that direction as well with their soon to be released Spark.

Still too heavy to meet the low weight regulations, but probably one more generation and they will be there.

Best regards,

Gary

Comment by Bob Morley on April 20, 2017 at 12:41pm

I agree completely regarding tricopter tail linkages, a vulnerable part that's tough to simplify, all part of the challenge. I have some ideas but ran out of space for the servo, it may yet happen as I'm still working on the CAD model.

Thanks for the helpful comments & ideas, I'll post an update when I start building.


MR60
Comment by Hugues on April 21, 2017 at 1:16am

Nice project. If I can throw some experience on building frames : they must be as rigid as possible in order to have a good attitude control. CF tubes are rigid, no problem. But PLA plastic parts are linking and holding your CF tubes and that is not going to be rigid enough (and also PLA break easily and ages quickly. ABS would be best but is harder to print). You should somehow design your frame so that CF tubes are glued and fixed together independently of your PLA parts (PLA parts can reinforce of course the overall solidity and rigidity). For the glue, the only one to consider is the 3M 2216 époxy (especially made for carbon fiber, has the right viscosity, has the strongest peel and rip resistance and has a final vibration resistance. It is the one used by Boeing in gluing plane parts...).

Thanks for posting and keep us up to date with your progress

Comment by Bob Morley on April 21, 2017 at 6:26am

I was just going to superglue everything and see how it went, nice to know which glue to use.

I agree PLA is a poor material but it has benefits - its cheap, easy to make accurate prints and can be used by every 3D printer. If it works out I may publish the design so it must be easy for others to make.

PLA ages & degrades badly, however I doubt it'll survive long enough for that to be important - something to do with my ratio of takeoffs to landings. Design, build, fly, crash, repeat.... :-)

Thanks for the tip on frame rigidity, there are ways to make strong parts from feeble materials so I'll redesign the way the CF tubes are linked.

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