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Author Topic: Twin 'Drone Motor' Douglas DC-5 (13")  (Read 667 times)
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Yak 52
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« on: November 03, 2020, 05:53:50 AM »

Knocked up a quick profile scale test bed for a peanut sized (13") twin electric using two 6mm coreless drone motors. Chaoli 615's shown here but I also have a couple of cheap Ebay ones to test my new Peterborough timer design and to give me some practical insight for a more scale small twin.

The Douglas DC-5 has a very favourable layout for free flight - modest aspect ratio for a transport, healthy dihedral and large tail volume - so the outlines and dihedral are true scale.

The weight of the sheet airframe is 9.9g. Adding motors, timer and battery will add up about 18 or 19 grams total. The Ebay motors should give me 12-14g of static thrust on a 100mAh lipo. The Chaoli ones are hotter with more like 20g thrust but draw more amps.

The timer is an etched circuit board version of the FET timer and uses a push button to start and trimpot to adjust the time from 0-80 seconds - no zapper required. It's pretty small at 8x12mm or 1/2" long. This one has a longish decay period so you get 60% of the run at full power and then a slow wind down. I'm hoping this will mean I get a good climb/cruise/glide style flight if I have matched the thrust to weight correctly.

Timer video: https://www.youtube.com/watch?v=EDzrv30bAZE


The timer is capable of around 5A and is intended as a plug and play option to make drone motors more easily used for outdoor sport free flight.


Jon
Attached files Thumbnail(s):
Twin 'Drone Motor' Douglas DC-5 (13")
Twin 'Drone Motor' Douglas DC-5 (13")
Twin 'Drone Motor' Douglas DC-5 (13")
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dosco
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« Reply #1 on: November 03, 2020, 07:37:21 AM »

That's neat. Have you flown it yet?

-Dave
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Yak 52
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« Reply #2 on: November 03, 2020, 07:44:57 AM »

Thanks Dave. Not yet - it's not finished but we have had a week of gales anyway  Roll Eyes
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Russ Lister
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Russ Lister



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« Reply #3 on: November 03, 2020, 09:28:04 AM »

Interesting project, Jon .... good to see you active with your FF stuff  Smiley
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RalphS
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« Reply #4 on: November 03, 2020, 10:14:39 AM »

That looks pretty neat Jon.  Currently starting my next r/c Micro Electric model, deH TK-4, along the lines of the foam Provost.  So when that is done will have to think about something else.  1S electrics are interesting keep the info coming.

Ralph
 
« Last Edit: November 03, 2020, 11:08:15 AM by RalphS » Logged
Jack Plane
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« Reply #5 on: November 03, 2020, 04:59:59 PM »

Nice!
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OZPAF
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« Reply #6 on: November 03, 2020, 06:10:45 PM »

That's interesting Jon. The variable run time really appeals.

Interesting choice of model as well.

John
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fred
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« Reply #7 on: November 03, 2020, 11:17:39 PM »

That's Great.. any info shareable for that intriguing timer layout / design?
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kaintuck
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« Reply #8 on: November 04, 2020, 06:50:23 AM »

Jon, very nice! Are you just simple wiring bothe the motors together? Nice props....can I ask your source...or did they just come with the motors.....I'm thinking the look a lot like internals from a duct fan......hummmmm indies!!! Grin
Marc
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Yak 52
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« Reply #9 on: November 07, 2020, 10:37:02 AM »

Thanks for the interest guys. I managed to finish off the model in time for some beautiful flying weather today. The model goes really nicely and I seem to have hit all my design points.

It came out at 17.7g and had just the right power-loading using the less powerful Ebay motors and Cheerson 3.7V 100mAh lipo. In other words the leccy bits come to 8g.

Motors: https://www.ebay.co.uk/itm/2x-3-7V-48000RPM-Electric-Aircraft-Coreless-Motor-with-Propeller-for-RC-Toy/202298895876 This link will probably expire at some point but there are lots of similar listings. The props are counter-rotating but the motors are not(!) so one is wired in reverse. These develop about 12-14g of static thrust so about 66% of the weight.

Here are some flight videos:
https://www.youtube.com/watch?v=IR9lQLXyP-g
https://www.youtube.com/watch?v=L09rfcsc39w

And some model blather:
https://www.youtube.com/watch?v=sXLDYBlu4rM
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Yak 52
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« Reply #10 on: November 07, 2020, 10:59:29 AM »

That's Great.. any info shareable for that intriguing timer layout / design?

Hi Fred, the timer is just a version of this circuit: http://www.peterboroughmfc.org/technical-articles2012/11ModifiedFETtimer.htm with an additional resistor for switch protection. It's an adaption of the basic Peterborough Timer that takes voltage from the flight battery to charge the timer capacitor. The 3mm trimpot sets the time. In this case around 1 minute - but anything up to about 5 minutes is possible depending on what capacitor/trimpot values you choose. You get a decay phase of about 25% of the total run time.

This one uses small SMD components on an etched circuit board of my own design. The FET can cope with around 5A so would run four of these 6mm motors comfortably. It weighs 0.3g ex wires. This is still at the prototype stage but I've got in mind to build them for sale at some point - the etching and tiny solderering takes a while though so it won't make me rich...  Roll Eyes




Jon, very nice! Are you just simple wiring bothe the motors together?

Hi Marc, the motors are wired in parallel - in this case both extension wires go to the timer motor output terminals. I've used 2 strands of 32AWG servo wire for the extensions - actually only rated at 0.15A but similar in size to the motor wires. A paired wire makes everything neat and Blenderm tape sticks them to the balsa.




Nice props....can I ask your source...or did they just come with the motors.....I'm thinking the look a lot like internals from a duct fan......hummmmm indies!!! Grin
Marc

These props are 31mm ones for the Tiny Whoop or Eachine E010 drones. I've also noted they might make a nice ducted fan  Cool but the issue will be making a really tight ducting. They give around 10-12g static thrust on the Chaoli 615 motors. (Sounds like you need a timer  Wink)

They come in 2, 3 and 4 blade options. Micro C-130 or Constellation anyone?  Smiley


Jon
Twin 'Drone Motor' Douglas DC-5 (13")
Twin 'Drone Motor' Douglas DC-5 (13")
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OZPAF
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« Reply #11 on: November 07, 2020, 05:42:03 PM »

Congratulations Jon - timer and model both working well.

I was a little surprised by the amount of right aileron as well as right rudder required to keep that nice right turn. It would have been a little easier to understand if you hadn't used contra rotating props. However the scale outlines work well and it could make a good scale contender.

John
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Yak 52
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« Reply #12 on: November 07, 2020, 06:01:17 PM »

Thanks John  Smiley

I think there are two reasons:

1) The right wing had a wash-in warp giving left roll (using up some mediocre wood)

2) The battery really ought to be mounted more on the centreline, maybe in a cut out. It's 3.5g and really pushes the CG off to the left. Either that or some blu-tac on the R wing tip to balance it laterally. I noticed the same effect on my little 8" Buffalo. If I'd been clever I would have mounted the battery on the right and offset the warp Cheesy

I think if I sort the lateral CG it should fly more consistently and react better to gusts. The motors have no sidethrust just a couple of degrees of down thrust. It could do with fettling a bit but it was fun flying it  Cool
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« Reply #13 on: November 08, 2020, 07:17:46 PM »

Ah! What seemed like a deep involved reason for the turn was actually quite simple and down to earth! Thanks Jon. Offsetting batteries or supercap's is very effective. My supercap model relies on this for glide turn.

I can't do anymore on the last one I built as I have lost it - flying in dusk and it vanished!

As for controlling the power turn - perhaps a slight thrust reduction on the inside of the turn - using a small resistor to drop the revs in lieu of side thrust?



John
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Yak 52
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« Reply #14 on: November 20, 2020, 02:02:17 PM »

I've just realised I posted the wrong ebay motors. The actual ones used are 612's (6mm by 12mm) nominally 50,000 rpm - whichI presume is the no load revs. https://www.ebay.co.uk/itm/2Pcs-DC-3-7V-52000RPM-6x12mm-Motor-w-Helicopter-CCW-Propeller-for-RC-Quadcopter/382419437020

There are lots of very similar looking small motors out there  Shocked I found some nice little 610's also which might be nice on a smaller twin.


I can't do anymore on the last one I built as I have lost it - flying in dusk and it vanished!

You'll have to build another John Smiley


As for controlling the power turn - perhaps a slight thrust reduction on the inside of the turn - using a small resistor to drop the revs in lieu of side thrust?

I'm not sure differential thrust is something I'd want to dabble with on a such a small model to be honest!

I've been drawing up a stick and tissue version of the DC-5 (which may or may not progress!)
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kaintuck
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« Reply #15 on: November 23, 2020, 01:58:44 PM »

Jon:
B-23 Dragon / UC-67
I have the balsa...
I have the motors....
I have the timer.....
 Cool
marc
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TimWescott
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« Reply #16 on: November 23, 2020, 03:05:28 PM »

... The FET can cope with around 5A ...

Uh, unless you design power electronics in your other life you may want to check that...  Most switching FETs are rated for the current they can carry when they're turned on fully.  This works because the voltage drop across the FET is small, even if the current is high.  During the decay period the FET will be partially on, so it'll have a higher voltage drop -- even with the reduced current, the total power that the FET needs to burn up will be much higher.

Clearly, what you have is working, but I'd check it anyway.

The test that the professionals use is to use one of the ten built-in thermometers that nearly all of us are issued with.  Run the thing on the bench while holding the FET between your fingertips.  If it gets hot enough during that decay period that you have to let go then the case is getting up to 50 degrees C or so.  Unless the part is rated for a junction temperature of 175C, then with no cooling from your fingers it'll probably get hot enough to harm itself in flight.

(Come to think of it, I might even buy one of those cheap $200 "clip on your phone" FLIR cameras and LOOK -- but that would be as much an excuse to get the camera as anything else)

Of course, if you do design power electronics in your day job, just ignore me.

... the etching and tiny solderering takes a while though so it won't make me rich...  Roll Eyes

Search for a PCB aggregator that sells into GB, and learn how to use solder stencils and do skillet reflow.  You may also have to learn how to design a PCB on a CAD program, if you're not doing so already.  The cost is time learning.  The benefit is that you can make a bunch of boards at once, and reflow is way faster than soldering by hand.

(I don't know how much Brexit has affected this -- there's a lot of good inexpensive PCB houses in eastern Europe; it's what I would have recommended to a pre-Boris Brit).

Just design your board, then panelize it (my local aggregator will do this for me, although I think I'd get the software to do it myself).  I'd make panels about four or five inches on a side, fab them, then snap them apart and finish assembly.

My skillet is a $5 kitchen skillet from Goodwill, accessorized by a cheap $20 thermocouple meter from fleaBay.  My local PCB aggregator (OshPark) is great, and they recommend a local solder stencil maker (OshStencil, no relation) that is also great.  Small lots of solder paste can be gotten as repair kits from DigiKey (so, probably Farnel where you are).  I'm soldering 0402 resistors and 0.5mm pitch LCC packages with good results now that I'm actually using the proper temperature profile (i.e., letting it soak long enough during preheat and the actual soldering phase).
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Yak 52
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« Reply #17 on: November 23, 2020, 04:04:51 PM »

Jon:
B-23 Dragon / UC-67
I have the balsa...
I have the motors....
I have the timer.....
 Cool
marc

Go for it! I suspect that monster sized fin may give you some spiral problems but why not make a little profile scale test bed?
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Yak 52
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« Reply #18 on: November 23, 2020, 04:09:56 PM »

Tim, yes you are right about the power dissipation - I did some rough calcs and used one of my ten my 'digital thermoprobes'. At the moment this model only pulls about 1A with both motors so it's not been an issue. I will test anything larger properly first especially with the long decay phase. It'd be less an issue with fast switching.

I haven't yet tried getting PCBs made but I have looked into it a little - something I'd definitely like to try in the future. I'll probably be picking your brains when I do Smiley

Jon
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TimWescott
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« Reply #19 on: November 23, 2020, 04:13:43 PM »

I haven't yet tried getting PCBs made but I have looked into it a little - something I'd definitely like to try in the future. I'll probably be picking your brains when I do Smiley

You're welcome -- I've done some power circuit design in the past, including a similar timer circuit for control line.  The only difference is that I made the timer "snap action" to avoid the power roll-off (because with CL you'd have been landing on grass at part throttle, which would not have been good).
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Yak 52
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« Reply #20 on: November 23, 2020, 04:23:15 PM »

I use a different circuit for a 'hard stop' timer for E20 competition models - it includes a prop brake. For these little 'sport' timers the slow decay is quite helpful.
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