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Author Topic: CC-115 Buffalo - 8" Profile Twin Electric  (Read 339 times)
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Yak 52
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« on: January 27, 2019, 09:32:34 AM »

I flew my little Buffalo at Bushfield today. It's a 8" profile model using twin contra-rotating 4x8mm motors, a FET timer and 25mAh lipo. All up weight is exactly 4g.

Colour is just felt tip pen and it was running out  Undecided I found that the yellow blushed bright red when thin CA was applied so it's not the ideal finishing method.

The motors give about 2.2g of thrust initially but this quickly drops away to a steady 0.7g and the battery voltage drops to 1.4V under load, so something is not quite right. I cut the props down somewhat and it was better - cruising around for 10 or so seconds happily enough. The model was sensitive but relatively easy to trim.

Early trim flight: https://www.youtube.com/watch?v=m6ZCVIqGu4A


Jon
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CC-115 Buffalo - 8" Profile Twin Electric
CC-115 Buffalo - 8" Profile Twin Electric
CC-115 Buffalo - 8" Profile Twin Electric
CC-115 Buffalo - 8" Profile Twin Electric
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MKelly
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« Reply #1 on: January 27, 2019, 11:16:58 AM »

That's very cool.  Ever since watching "The Adventures of Yellow Dog" I've had the itch to build a model of this aircraft.  I'd be most interested in hearing updates as your trimming progresses.

Mike
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« Reply #2 on: January 27, 2019, 06:26:54 PM »

Thanks Mike - yeah I've had a thing for the Buffalo for a while too - I fancy a big rubber twin version in 'Starleaf' scale. The trimming went surprisingly well considering the small size. I scaled the wing up by chord (it's pretty low on area) but the tail surfaces are scale (tail volume is massive, even with increased wing area.) It has scale dihedral so I think a bigger one would be viable. The only issue might be the overlarge fin, but hopefully it would be countered by the nacelles and big props.

Jon
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OZPAF
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« Reply #3 on: January 27, 2019, 07:14:05 PM »

Neat Jon - that would probably do well on a supercap and possibly would be no heavier.

John
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MKelly
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« Reply #4 on: January 27, 2019, 10:32:14 PM »

If you go with the supercap do you still need the FET timer?

Mike
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« Reply #5 on: January 28, 2019, 07:02:01 AM »

That's very nice Jon, and interesting. I'll be watching to see how it develops. I read somewhere else on HPA that the motor is most efficient at 75 to 80 percent of no-load rpm - could that be a factor in "something is not quite right"? I've been working up an enthuiasm for this supercap malarkey, and I may even unchain and unpadlock my wallet to buy some gear.

Quote from: OZPAF
Neat Jon - that would probably do well on a supercap and possibly would be no heavier.
Quote from: MKelly
If you go with the supercap do you still need the FET timer?
I thought probably that the capacitor would be lighter than the equiv. battery though perhaps bulkier? If the battery is lighter then why bother with capacitors - is it to save having to charge LiPos or is it because some intermediate electronics between motor and battery is essential with LiPos?

The yellow marker/CA thing can be used when you want to verify that the glue has reached a certain area - I use it on long seams such as a butt-joint along a balsa tube. Some yellow marker pen along the seam edge, close the join and then it goes bright red when CA wicks into the join.

Stephen.
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Yak 52
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« Reply #6 on: January 28, 2019, 05:19:05 PM »

Thanks guys.

Yes, definitely in the area where a supercap is as good as lipo. That said the 1S 25mAh lipo I used is only 0.96g including connectors. The timer is this one: http://peterboroughmfc.co.nf/technical-articles2018/Miniaturising_FET_Timers.htm it's only about 0.2g exc connectors but a capacitor wouldn't need one. I have a 1F 2.5V supercap that weighs similar at 0.92g but whether it would have the required power or duration I'm not sure. That's only 2.5 amp/seconds. I'd guess the amp draw is around 75mA for each motor so only 16 seconds at 150mA (not that you'd get constant current - you don't.)

I read somewhere that these 25mAh lipos can give up to 80mA so they probably just aren't good enough to handle a twin. Motor testing as a single engine worked better. I probably just need a bigger or better battery. I'm afraid I just chucked this together quickly and didn't measure amp draw (tricky on such a small model) or use a tacho for load/no load RPM. I did put it on the thrust rig though. The motors are just cheapies from ebay with Cheerson CX-10 31mm diameter drone props.
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« Reply #7 on: January 28, 2019, 06:40:13 PM »

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If you go with the supercap do you still need the FET timer?

No I don't think you would Mike. The power delivery of the super caps is supposedly similar to rubber and the model  would land with motor still running.

For a small indoor model it would probably be best to just have a straight direction connection from the super cap to the motor and a charge point.

Here is a example https://www.youtube.com/watch?v=-GyeYgdHZcw

Outdoor models often use small switches.

Happy flying

John
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MKelly
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« Reply #8 on: January 28, 2019, 07:37:27 PM »

Thanks John, that was a good demonstration video.  I need to learn more about this...  I have a tiny drone found in the neighborhood park that no one has claimed - might have to cannibalize it and do some experimentation along the lines of what Jon is doing here.

Mike
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