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Old Nov 12, 2012, 02:18 AM
Registered User
DeBary, FL
Joined Nov 2010
1,450 Posts
Discussion
brushed ESC control of fan/blower motor

Background. There's an interesting post about an electric plane flour-smoke generator at http://www.rcgroups.com/forums/showp...0&postcount=47 which even though it didn't work very well got me thinking. Its' main advantage is that it's not really a '$5.00 smoke generator' it's more like US0.14. LOL! The problem though is that it uses only the airplane's airspeed to force air coming in one hole to stir up the flour, and the low pressure of the 9 holes at the back end to draw the air out. Well there's not enough airspeed or turbulence to stir up the flour.

The turbulence thing. The main reason the above design doesn't work very well is that the flour just sits there and there's nothing to stir it up into suspension. So I'm thinking about what to do about -forcing- more air to make more turbulence and then also -push- the flour out. My intent is to add a tube that pokes down into the flour, and forced air 'bubbles up' through the flour and puts it into suspension.

I tried a tiny RS fan rated at only a few cfm, plus a 'neck-down' kind of venturi to make more speed, but it had no ability to create any pressure or turbulence and so failed.

So, how about at small air pump: http://www.skycraftsurplus.com/12vdc...gmairpump.aspx To save folks looking at that page it's 12V 300mA 2L/min 0.5lb. It's less cfm but it's a diaphram -pump- and has lots more -pressure- if not volume than the RS 'fan.'

If that doesn't work I'll try http://www.skycraftsurplus.com/dcfbb...Ifan12vdc.aspx That's still technically a fan but tons more cfm and more of a blower type assembly housing which means lots more pressure. It looks a lot like what I have for cooling fans in my laptop. That one is 0.68A and 23cfm 4.8oz.

In any case my Q here is how to power these devices.

I would like to use brushed ESC such as http://www.gravesrc.com/GPMM2005_GP_...p/gpmm2005.htm

I'm half hoping that running these 12V-rated devices won't turn them to toast at 12.6V of a fully charged 3s lipo. The alternative is 4s plus voltage regulator to get past the dropout. If I have to do that I'm not concerned about extra weight of another cell plus regulator because this is going into a Sig Kadet Senior with Hacker A60 and tons of extra thrust, but I'd still rather avoid the weight if possible and the annoyance of building more stuff.

The main reason I want to use ESC rather than simpler on/off control is that I can mix throttle to the blower speed / smoke volume.

And here's the -real- guts of my Q... The way I understand what I've been reading, I would:

- Disconnect ESC power wire where it plug into receiver.

- Connect battery power to ESC battery input. (3s, or 4s plus regulator.)

- Connect battery ground to ESC ground (which I'm guessing is internally commoned to the servo port ground.)

- Connect ESC + and - output leads to fan/blower.

I think that as long as whatever resistive device I attach is within the limits of the battery and ESC capabilities, and keep the auxiliary device +V away from the receiver/main battery/flight battery +Vs, I should be OK.

Actually if it comes to it I don't see any small-mA 4s batteries but I know how to connect 2 2s batteries in series.

Does it look like I have a clue about what I'm doing? Do I need to buy a vowel?

Yes I know the ESC is way overkill on the power load capability side of things but I'd really rather not deal with the time and annoyance of breadboarding this stuff.

TYVMIA

Jim
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Old Nov 12, 2012, 06:14 PM
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Bruce Abbott's Avatar
Hastings, New Zealand
Joined Jan 2001
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Quote:
Originally Posted by jbarchuk View Post
I'm half hoping that running these 12V-rated devices won't turn them to toast at 12.6V of a fully charged 3s lipo.
The GP C-7 NANO is designed to work on 3S Lipo, so it should be fine. The only problem you might have is with arming, as it needs to be cycled from low to high throttle and back. Most other ESC's (eg. Blue Arrow PP-10C) just need low throttle to start.

You are correct that the red wire must be removed from the servo plug, to disable the BEC. The battery ground and servo signal ground are joined together inside the ESC, so no extra ground wire is required.

Quote:
Actually if it comes to it I don't see any small-mA 4s batteries but I know how to connect 2 2s batteries in series.
I suggest using a small 3S Lipo. This will put out close to 12V, which is the correct voltage for those pumps/fans.
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Old Nov 12, 2012, 11:15 PM
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DeBary, FL
Joined Nov 2010
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Quote:
Originally Posted by Bruce Abbott View Post
The GP C-7 NANO is designed to work on 3S Lipo, so it should be fine. The only problem you might have is with arming, as it needs to be cycled from low to high throttle and back. Most other ESC's (eg. Blue Arrow PP-10C) just need low throttle to start.
Totally doable. The Senior I'm doing this with first has a separate motor ESC arming interlock. I power up the receiver with a switch first, check out the surfaces, and then arm the motor. With the receiver check I can move the throttle up and the motor doesn't move, but it will arm the smoke ESC. Then I turn -off- the switch that enables the throttle-smoke mix so I don't gum up the whole taxiway with flour and tick everyone off. LOL!

Or maybe for testing first I'll put the smoke on a dial control, and try the throttle mix later.

Quote:
You are correct that the red wire must be removed from the servo plug, to disable the BEC. The battery ground and servo signal ground are joined together inside the ESC, so no extra ground wire is required.

I suggest using a small 3S Lipo. This will put out close to 12V, which is the correct voltage for those pumps/fans.
Excellent and excellent, thanks.

Every word I read always clicks off another idea in my head. Where you said 'pumpS/fanS.' The 'pump' might put out enough -pressure- to stir up the flour, but not enough volume to move a significant amount of air. The 'blower' might move a lot of air, but with very little force. So, I might even end up using -both- - the pump to stir up the flour and the blower to push lots of it out. (I had thought about a servo or other small motor mounted on the top of the flour container, running continuously 360deg, with an arm going down into the flour and a 'stirer' to thrash around and put the flour into suspension. If the pump doesn't do it that's a second possibility but the difficulty is pressure and flour leakage into the interior of the plane. It'll be tough enough building a well sealed box without adding another hole.)
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