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Author Topic: 24" scaled down FF epower  (Read 443 times)
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jerryCashman
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« on: August 16, 2019, 02:25:33 AM »

Hi guys - I've been toying with the idea of trying some scaled down versions of the classic FF models from the 50's and 60's for a while. Veron Cardinal, Tomboy, that sort of thing.

I'm thinking of aiming at 24" span (down from the originals which were about 36" or so) and am thinking of using the power package and timer described by Jonathan Whitmore recently for the Ferry 500. http://peterboroughmfc.org/Ferry500.html

I'm hoping that the power system from the Ferry 500 will yield a gentle sport performance with the extra weight, span and drag from a full fuselage model and should slow things down a bit...

I'm sure I'm not the first to think of this - has anyone tried these power systems in built up 'sport' type models of around this size?

cheers. Jerry in Oz




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Yak 52
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« Reply #1 on: August 16, 2019, 08:59:04 AM »

Hi Jerry,

Great idea - this kind of sport flying is pretty much what the Peterborough Timer was developed for. Ian Middlemiss (originator of the Ferry 500 class) and others in the PMFC have done the same thing in the past.

I have a feeling that the Ferry 500 power train - CN12-RXC on 2S with a 3x2 prop - might be a bit on the warm side for a 24" Tomboy since it gives you around 75-80g of static thrust. It depends on the model weight obviously but at that size you might be better with an 8.5mm geared motor on 1S providing you build nice and light. The one from SAMS is very good: http://www.samsmodels.com/products/electric-flight/sams-electric-motor-gearbox-unit it will fly a lightweight (30-35g) Open E20 on a 5x3 prop and outperform the Ferry 500. Parkzone or Voodoo might be other options.

Ian flew his 23" Strato Streak on the CN12 but on 1S - good for about 30g of thrust, but a decent coreless drone motor such as the Racerstar 8520 would give at least that at half the weight on a 65mm direct drive prop.

A couple of old threads of Ian's may be of interest:
https://www.hippocketaeronautics.com/hpa_forum/index.php?topic=11587.msg77828#msg77828

https://www.hippocketaeronautics.com/hpa_forum/index.php?topic=12545.msg88862#msg88862

https://www.barcs.co.uk/forums/topic/5781-electric-free-flight-design/

The other thing to consider is that a small prop on direct drive might lose thrust if blanked by a large nose/fuselage - gearing and a bigger prop may be more efficient. A geared CN12 is a successful option in E30 on 1S at 100 grams.

The Peterborough Timer suits any brushed or coreless motor though. I have recently started making Ferry 500 timers for sale and can provide other versions too such as adjustable run time. If you would like anything specific I can build to your specs and post them out, so feel free to get in touch or just to ask for help on adjusting times and components if you want to make your own.

Let us know how you get on!


Jonathan (Whitmore)
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jerryCashman
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« Reply #2 on: August 19, 2019, 08:19:21 AM »

Thanks for taking the time to reply Jonathan,

Thanks also for the advice re: power trains - sounds like a fun format to experiment with!

We've got a pretty good supplier of small bits and pieces here in Aus - Micron Wings up in QLD (no affiliation). They have a few motor/gear units that look similar to the SAMS unit so there's a few things for me to try :-)

https://micronwings.com/Products/SectionGeardrives/index.shtml

I'll update when I've got something flying :-)

cheers. Jerry
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Yak 52
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« Reply #3 on: August 22, 2019, 02:46:40 AM »

Some great stuff on the Micron Wings site  Smiley I particularly like the look of the little 4mm gearboxes!

Let us know how you get on  Smiley

Jon
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jerryCashman
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« Reply #4 on: September 06, 2019, 01:57:42 AM »

Well, some slow progress to report - I girded the loins and fired up the soldering iron last night and made my first Peterborough timer - and the sodding thing worked first time - VERY satisfying :-)

It's only three components - but was very enjoyable to hit it with the 9v battery and have that little prop sing into life... (actually it took off across the bench as I didn't think I'd get it right first time and hadn't weighed the test stand down ;-)

I used a 220k resistor and am getting about 15 seconds run from a 1S cell with a 12mm motor and 3*2 GWS prop. I'll try that first and if things are tentative, can step up to 2S...

I'm wondering now if it's possible to add some form of throttle to the circuit? Understand you want full noise for comp use, but for gentle sport use it might be nice to be able to dial-in power/thrust?

Now: on to the airframe: https://outerzone.co.uk/plan_details.asp?ID=8183

cheers. Jerry

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Yak 52
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« Reply #5 on: September 06, 2019, 10:01:41 AM »

Nice! I'm glad it worked  Smiley

I'm wondering now if it's possible to add some form of throttle to the circuit? Understand you want full noise for comp use, but for gentle sport use it might be nice to be able to dial-in power/thrust?

This is the one downside to the Peterborough Timer - lack of throttle control - but that is the price of simplicity. It is quite possible to make a circuit that will give thrust control by pulse width modulation but it adds a fair bit more complexity. A simpler way is to add a resistor to the circuit but these would need to be rated for the appropriate power to avoid them burning out and you waste some energy.

Otherwise it's a case of sizing the model correctly in the first place, playing with prop size and pitch, reducing the battery size to limit voltage (within bounds of C-rating) or adding drag and weight to the airframe to keep the climb under control.


Jon
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raggedflyer
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« Reply #6 on: September 08, 2019, 02:34:06 PM »

Just pondering if it might be worth investigating a 3 terminal adjustable voltage linear regulator to supply voltage to the motor as an alternative to pulse width control in terms of cost and minimal components.
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dputt7
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« Reply #7 on: September 08, 2019, 08:14:07 PM »

A very easy way to control the power out put is to trim the prop down!
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Yak 52
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« Reply #8 on: September 09, 2019, 02:58:05 AM »

Just pondering if it might be worth investigating a 3 terminal adjustable voltage linear regulator to supply voltage to the motor as an alternative to pulse width control in terms of cost and minimal components.

I looked into this a while back but there are a few issues: you still have the power dissipation problem - they get really hot. Also there's a fair drop between the input and output voltage. I did see a circuit utilizing the linear region of a FET to add resistance but its a fairly crude solution. I think PWM is the way to go really.

The beauty of the Peterborough timer is it's simplicity but it obviously has some limitations.
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OZPAF
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« Reply #9 on: September 09, 2019, 03:40:30 AM »

What about a small brushless timer and ESC from Dens Hobbies( control line supplier) - or maybe just the timer and source a small ESC elsewhere?

John
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