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2 channel & low voltage cutoff

Old 08-13-2007, 04:36 PM
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joe_rosevear
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Default 2 channel & low voltage cutoff

Dear electric flyers,

I'm new to electric, but not new to RC flying. I have a ten-year-old 2 channel radio (Hitec Focus) that I would like to use to try out electric flying. It has BEC circuitry, but I think I need a low voltage cutoff too.

So how can I manage that? I figure I could get 2 or 3 LiPoly cells, a motor and an ESC. And I understand that the ESC will likely have a cutoff function, but...

I wondered if anyone had tried this with a two-channel radio? What will the throttle control of the ESC do with no throttle channel being transmitted to the receiver?

So maybe I can use a regular (brushed) motor, no ESC, and a stand-alone cutoff module. Does that exist?

Thanks in advance. Hope you can help.

-Joe
Old 08-13-2007, 09:08 PM
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jdetray
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Default RE: 2 channel & low voltage cutoff

Hi Joe -

With a 2-channel system, how will you control the throttle? Without a throttle channel, an ESC can't control a motor.

With a brushed motor, you could wire the motor through a switch directly to the battery, switch it on before flight, then fly at full throttle until the battery is depleted. It would not be a very pleasant way to fly, going full speed all the time. Lipos would be fatally damaged if you did this, but NiMH batteries can tolerate being fully discharged.

There is probably some clever way of arranging the servo linkages to flip a switch that would turn the motor on and off. E.g. -- a momentary application of full left and full up would turn the motor on, and full right and full down would turn the motor off. I seem to recall hearing of such things in the dim past.

My apologies if I have mis-interpreted your query.

- Jeff
Old 08-14-2007, 12:40 AM
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mrasmm
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Default RE: 2 channel & low voltage cutoff

there ie EQ out there that will do something like a soft off, but it would do it through an ESC, so I dunno how you would manage that, but one is available at www.commonsenserc.com

Also you can pick up a decent 3 or 4 channel radio off of ebay for 30 to 50 bucks, so you could look at that route.

welcome to RCU =)
Old 08-14-2007, 03:50 AM
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joe_rosevear
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Default RE: 2 channel & low voltage cutoff


ORIGINAL: jdetray

Hi Joe -

With a 2-channel system, how will you control the throttle? Without a throttle channel, an ESC can't control a motor.

With a brushed motor, you could wire the motor through a switch directly to the battery, switch it on before flight, then fly at full throttle until the battery is depleted. It would not be a very pleasant way to fly, going full speed all the time. Lipos would be fatally damaged if you did this, but NiMH batteries can tolerate being fully discharged.

There is probably some clever way of arranging the servo linkages to flip a switch that would turn the motor on and off. E.g. -- a momentary application of full left and full up would turn the motor on, and full right and full down would turn the motor off. I seem to recall hearing of such things in the dim past.

My apologies if I have mis-interpreted your query.

- Jeff
Jeff,

Sorry I wasn't clear. I don't want a throttle. That's why I'm flying with a two channel radio. It is a time honored way to fly and actually a whole lot of fun. The power takes you up. Maybe you find a thermal or two while you're up there. Then you come down. Or if you don't want to climb, then just have fun buzzing around. I learned to fly R/C on a 1/2 A powered Q-tee (2 channel: rudder and elevator). So this is quite natural for me. Later I put a 1/2 A power pod on a Wanderer (glider) and that was great.

Are you familiar with the LVC (low voltage cutoff) feature of ESCs? Yes, I understand you would ruin LiPolys by running until they go flat. And if you were using a Battery Eliminator Circuit (BEC), then that would likely boggle also. That's why ESCs have an LVC. I learned this (hope it's true) doing some web research.

I'm just wondering if anyone had tried using an ESC without connecting it to the receiver. Does it behave as a full throttle LVC?

Or maybe someone knows of a stand-alone LVC so I wouldn't have to use an ESC. (I suppose I could make one.)

Your suggestion of using Ni-MH is a good one. I might do that. But... I would really like the benefit of an LVC.

I don't think I want a rudder actuated switch. Thanks, anyway.

-Joe
Old 08-14-2007, 07:04 AM
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Leo L
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Default RE: 2 channel & low voltage cutoff

Hi Joe,

Seems like a whole lot of trouble to go through just to use an old radio. As Mrasmm said, you can go on e-bay and buy a good 4-channel for only a few bucks, or you can buy a replacement radio for an RTF. I bought the ParkZone Typhoon transmitter last year for $30. The receivers are $26 each, so I have outfitted a half dozen planes with them. The radio is not fancy, but it does a great job of basic flight control. Set up your plane with a conventional set-up, get it up high and turn off your trottle. You can do all of the gliding and thermals that you want, yet you will still have control of the motor to go back up for another round, or to land with power and control.
Old 08-14-2007, 09:58 AM
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jdetray
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Default RE: 2 channel & low voltage cutoff

Hi Joe -

I was closer to understanding than I thought. And I have a possible solution for you.

You can operate an ESC without connecting to a receiver. Instead, you connect the ESC to a servo tester. This is in fact what I do with my electric motor test stand. I didn't want to dedicate a receiver to it or require a transmitter to test a motor.

You can see the unit I use here:
http://www.hobby-lobby.com/servos.htm

It's about 2/3 of the way down the page, the Esky Manual Servo Adjuster ($12.90). It is tiny and weighs only 8g.

To use it, plug the control cable from the ESC into either servo connector on the servo tester (NOT into the BATT connector). Connect the motor and battery to the ESC as normal. Now you can control motor speed with the knob on the servo tester.

So you can set the motor speed to your liking and fly the plane. When the battery voltage gets low enough, the LVC in the ESC will cut power to the motor to protect the battery, so you can use lipos.

If you can find a double-ended female servo cable, you could run it from any connector on the servo tester to the receiver, allowing the ESC's BEC to provide power for the receiver and servos. Otherwise, you could use a separate battery or a standalone BEC to power the receiver and servos. Here's one example of a standalone BEC:
http://www.dimensionengineering.com/ParkBEC.htm

I hope this helps!

- Jeff
Old 08-14-2007, 05:22 PM
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ozrcboy
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Default RE: 2 channel & low voltage cutoff

Hi Joe,

Jeff's servo tester sounds like a great idea. I was going to suggest that you program your LVC on your ESC for the highest possible cutout. Obviously you are planning to glide for as long as possible (that's the idea right) after the power cuts. My only concern would be you might overdraw the battery through the BEC, unless you want to use a separate flight pack for the RX/Servos (which seems like a lot of extra weight which it would be good to avoid).

When I think about it you are going to have to make up a special two headed wire harness for the ESC - one goes to your receiver so the BEC can power it, while the other goes to the Servo Tester or whatever you use to deliver power.

Cheers,
Oz.

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