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4hv.org :: Forums :: General Science and Electronics
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Electric Motor Effciency (Density / Watt / Losses)

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Patrick
Fri Nov 22 2013, 04:55PM
Patrick Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
ive since fixed the pilot induced oscillation problem, and ive decided to try a 5 degree dihedral on my new machine.

ive also decided to build a thrust stand in the project section here on the forum, and get real numbers so we can make more useful assesments of my situation.
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Patrick
Wed Nov 27 2013, 06:01AM
Patrick Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
Tomorrow I've planned a check flight with a 6000 mah , 480 gram battery on board. This should double the flight time, since the All up weight remains the same. I'm expecting 8 minutes in the air.
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Patrick
Fri Nov 29 2013, 04:49AM
Patrick Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
test flight successful.

8 minutes, 55 seconds til an "un - commanded landing. No damage done.

Total mass = 1.56 kg
Battery = LiPo, 3s, 480 gram, 6000 mah, 11.1 V.
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BigBad
Sat Nov 30 2013, 05:16PM
BigBad Registered Member #2529 Joined: Thu Dec 10 2009, 02:43AM
Location:
Posts: 600
Matter of interest, your fiber layup, how do you impreg it, are you spraying it or something? It looks quite thin, very low weight.

I need to build a rigid structure for a weirdo motor I'm building and a foam cored fiber layup might be quite good. At the moment I'm using balsa, but FG or CF is potentially rather better, so I'm interested in how you formed it.
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Patrick
Sat Nov 30 2013, 10:01PM
Patrick Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
BigBad wrote ...

Matter of interest, your fiber layup, how do you impreg it, are you spraying it or something? It looks quite thin, very low weight.

I need to build a rigid structure for a weirdo motor I'm building and a foam cored fiber layup might be quite good. At the moment I'm using balsa, but FG or CF is potentially rather better, so I'm interested in how you formed it.

I would recommend E or S2 fiber glass to learn on first. Your mistakes will be cheaper that way.

Let me post some more pics in a few hours, I'm sick at the moment....

carbon fabric is conductive, but I need to measure itagain. Not sure if that's a pro or con for your purpose.
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BigBad
Sat Nov 30 2013, 10:32PM
BigBad Registered Member #2529 Joined: Thu Dec 10 2009, 02:43AM
Location:
Posts: 600
Yes, I plan to use GF for those reasons. I've got no current plans to use CF at all, I've also got to produce more than a dozen copies, so I'm expecting to make a few examples before getting it right.

I've made and worked with heavyweight GF before I just wanted to know good ways to make lighter fiber stuff.
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Ash Small
Sun Dec 01 2013, 12:09AM
Ash Small Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245
Use a thin woven 'S' glass, I think.

If my memory can be trusted, 'E' glass is the cheap stuff.

Use a good quality epoxy. West Systems is good if you are State-Side.

EDIT: Googling 'West Resins' might work as well.
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Patrick
Sun Dec 01 2013, 04:24PM
Patrick Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
E-glass is cheapest. S-Glass is more expensive, arimid and CF are most expensive.

Ive PMed BigBad for details, ill start a post soon in the projects section.
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Patrick
Sun Dec 08 2013, 04:44PM
Patrick Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
ive got new info here:


1386521084 2431 FT157199 Right Esc
there appears to be about 300 rpm of variation off the normal 5500 rpm. This is the pid control commanded rpm change. I was holding it in level flight. I'm calculating how much power is lost in this process.


1386521084 2431 FT157199 Right Esc Rpm Watts
power used to hover is about 130 watts times 2 = 260 watts for the forward c two fans.

I'm wondering if a variable pitch prop, like a tail heli's, would be a net advantage. Or just more weight and cost.
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BigBad
Sun Dec 08 2013, 06:18PM
BigBad Registered Member #2529 Joined: Thu Dec 10 2009, 02:43AM
Location:
Posts: 600
Patrick wrote ...

ive got new info here:


1386521084 2431 FT157199 Right Esc
there appears to be about 300 rpm of variation off the normal 5500 rpm. This is the pid control commanded rpm change. I was holding it in level flight. I'm calculating how much power is lost in this process.
Off hand, I would think that to a first approximation none, since L/D ratio doesn't vary much over that speed range.

Or if it is significant, you've not matched the rotor properly, the L/D curve should be flat near to the hover speed.
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