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Old Jun 16, 2001, 09:51 AM
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Frederiksberg, Denmark
Joined May 2001
79 Posts
Speed control and diode ?

Hi

I just got my new Ripmax xtra-22 speed control for usage on my Wingo.

And I guess that the best thingis to disable the brake, so I wont have the propeller dragging, but am able to let it freewheel.

There is a big diode together with the control, but no mentioning of it in the instructions.

Should I solder this into the positive wire form the speed control to the motor ?

What does it do ?

Can I hurt the speedcontrol if I dont solder the diode inti the positive wire, and the motor freewheels and acts like a dynamo ?

JJ
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Old Jun 16, 2001, 11:07 AM
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Ijamsville, MD, U.S.A.
Joined Mar 2001
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Jens; You must be certain that the banded end of the diode points to the + output from the ESC. If you reverse it, you will ruin the ESC. Please look at www.fmadirect.com ; click on FAQ; and read the section re electrical noise. Having the diode in the circuit does two things: 1) Cuts electrical noise because it rectifies noise from the motor brushes and 2) absorbs inductive kick as the motor field collapses and converts it to DC(Which improves effficiency)
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Old Jun 16, 2001, 11:08 AM
Radix malorum est cupiditas
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Joined Jul 2000
460 Posts
Jens,
solder the diode across the motor terminals, make sure that the positive lead from the speed control goes to the banded end of the diode. The diode provides a path for the inductive currents generated by the switching of the ESC.

There really should be some directions with your speed control (with diagrams) to show how to install the diode.

The diode will not have any effect on the braking function of the esc.

With a plane like the Wingo, and most slow flyers, you will be keeping a little throttle on during landing typically.

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Old Jun 16, 2001, 02:45 PM
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N. Staffs, UK
Joined Jan 1997
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And you don't want to disable the brake. A freewheeling prop has a lot more drag than a stopped one. The brake is a good thing.

Steve
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Old Jun 16, 2001, 03:38 PM
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Roxboro, NC U.S.A.
Joined Sep 2000
714 Posts
Be sure to check and double check which end you solder the stripe on the diode to. I just trashed a new speed control by doing this backwards. Bad, very bad!!!! Battery got hot and smoke commenced to rising from the speed control. Tried to repair this myself and caused more damage but the folks at FMA gave me a discount on a new one. What they call the crash and burn policy!!
Fitting title. I can bet that I NEVER make that mistake again.
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Old Jun 16, 2001, 03:43 PM
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Houston
Joined May 2001
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why does a freewheeling prop have more drag?
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Old Jun 16, 2001, 05:23 PM
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Frederiksberg, Denmark
Joined May 2001
79 Posts
Thank you very much everyone for the info.

1. A diode soldered with the band going to the negative cable, is indeed a very bad thing. Anyone able to say shortcut ? I should have thought of that myself.

2. Well I had thought of inserting the diode into the positive weire, as a protection against current running back into the ESC. But I can also understand the idea of placing it going from the negative to the positive wire, as a sort of "rectifier".

3. A braked propeller gives less drag than a freewheeling one ? I can partly understand this, but I would like to read some background info, to help me understand it better.

Happy flying

JJ http://www.zorck.dk/rc - Now with Wingo building
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Old Jun 16, 2001, 11:23 PM
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Ijamsville, MD, U.S.A.
Joined Mar 2001
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Jens; A freewheeling prop presents a "flat-plate" area to the air equivalent to the rotation speed and blade area. The Rolls Roysce Dart engines (And others) with turboprops used flat pitch rather than prop reversing for braking during landing. The blades were brought to flat pitch and accelerated to make the flat plate area maximum. Helicopter performance is calculated on the basis of "solidity", i.e., the blade area X RPM is hthe measure. Same thing.
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