motor cutoff

[mdgretz]

I'm flying a scratch-built Speed 400 powered control line model.
Speed 400 (7.2v)
direct drive
6x3 Cox gray prop
(8) 500mah nicads (onboard airplane)
.008 x 30' control lines

I am presently using a small micro switch to shut off the motor. It is triggered by a quick application of full down elevator. It works fine, except that I cannot fly outside loops without it going off and stopping the flight prematurely. What I'd really like to have is a simple low voltage cutoff. When the battery drops to a certain voltage, it simply cuts off power to the motor.
Any ideas?

[realglow]

Originally posted by mdgretz:
I'm flying a scratch-built Speed 400 powered control line model.
......
What I'd really like to have is a simple low voltage cutoff. When the battery drops to a certain voltage, it simply cuts off power to the motor.
Any ideas?

You need a BEC (battery eliminator circuit). It is used by electric RC flyers to provide drive power to the receiver from the motor drive pack; it usually supplies 5v. When the drive pack drops to a predetermined voltage, the BEC cuts off the motor thereby leaving enough power to the receiver and servos to land the RC plane. BECs are usually built into the motor control unit for electric RC models, but I have seen BECs as stand-alone units (no drive output for the motor). I have one built by HITEC, but not sure if it is available now.

[DICKEYBIRD]

mdgretz:

Sounds like exactly the e-power u/c I would love to build! What are the wing area, airfoil and finished weight specs? Ya' wouldn't just happen to have a .dxf file of it would'ja?

As far as a motor shut off device, I liked a previous poster's suggestion that mentioned a user adjustable electronic timer shutoff device. I would like to have one with a startup timer as well so you could push a button to arm it, set the plane down, walk out, pick up the handle and the motor switches on for an ROG! Hmmm, a 2 function FF auto rudder/DT timer might be a good start.

Surely one of you techno-gurus out there can whip up a simple circuit that anybody could build, weighs 10 gms. or less and can be built out of R/Shack stuff, CHEAP!

I can always dream!

Milton Dickey

[jrb]

Check out the MARCEE site (its moved and I have the address at work -- though it might be in another recent posting).

In the articles section it has a ciruit used to shut-off battery packs during discharge.

Uses a relay that is set with a momentary switch, then drops off @ low voltage like ASO w/BEC!

Works neat.

[realglow]

It should be a simple matter to design an infrared transmitter into the u-control handle and an infrared receiver in the plane. Then you could set up your plane, walk to the handle and start the engine. You could also kill the engine anytime during the flight. A little more advanced design would let you control the motor speed during takeoff and flight.

[Bob Chiang]

EMPS sells an electronic "shut off" timer meant for free flight (so the time range is from 15 seconds to 2 1/2 minutes), up to 15 amps, but has a 6 cell limit.
http://www.empsinc.com/catalog.html#Timer

[jrb]

Here's the link: http://ijcooper.20m.com/Hobby/autodischarger.htm

All the components can be easily resized, reapackaged, and hard wired for any motor/cell combo.

[dr.E]

This has been done and it seems to be the way to go.

[Pierre Audette]

There's probably a way to adapt Stefan's circuit to use only the BEC portion. http://www.capable.on.ca/escbec.htm

[mdgretz]

Just returned home from the weekend. Glad to see so many responses.

realglow: I don't understand how a typical BEC can help me since I don't have a receiver to plug it into and make it work. I realize that BECs have low voltage cutoff built-in, but how do I utilize just that part without a receiver? About infrared, do you have more info. It sounds a lot heavier than the .35 oz. microswitch that I have now. Weight is of the utmost importance in order to keep it aerobatic.

DICKEYBIRD: Here are some more specs on the airplane.
Wingspan 27"
Wing Area 241 sq.in.
Wing Loading w/8 cell,500mah battery pack is 6.7 oz/sq.ft. (a SIG SKYRAY .049 powered C/L model has a 7.2oz/sq.ft. wing loading - so I've beat that!)
Airfoil: NACA0015
Delta configuration. Battery pack fits inside root of right wing.
I can send you a .dxf file - give me your email address.

jrb: Being a total dunce about electronics, this is all greek to me. What part of this device do I need? I'm confused.

Bob Chiang: An electric timer cutoff might be a good answer, but how do I get more time and more cells?

Don't get me wrong fellows. I really do appreciate the input. But I still feel that a simple low voltage cutoff (or timer) would be the best way to shut off the motor for the least amount of weight.

[jrb]

Should only need: the relay, 2 resistors (depend on cell count), & a momentary switch.

Understanding Ohms Law and how a voltage divider works is should be all the electrical know-how that should be needed.

[mdgretz]

Here's a link to a couple pics of my airplane. http://showcase.netins.net/web/mdgretz/

[DICKEYBIRD]

Mike,

Now that is one fine machine! But I'm jealous....it must be nice to have a CNC laser to cut out your toys. I cobbled up a home built CNC router from various pieces but can only dream about a laser!

Being a delta, does it bleed off a lot speed in looping manuevers? I designed/built a couple of R/C deltas but found that they slowed down a bunch when turning tight.

Milton

PS: My email for the .dxf file is mdickey@bcjag.com

[This message has been edited by DICKEYBIRD (edited 04-17-2001).]

[realglow]

Originally posted by mdgretz:
Just returned home from the weekend. Glad to see so many responses.

realglow: I don't understand how a typical BEC can help me since I don't have a receiver to plug it into and make it work. I realize that BECs have low voltage cutoff built-in, but how do I utilize just that part without a receiver? About infrared, do you have more info. It sounds a lot heavier than the .35 oz. microswitch that I have now. Weight is of the utmost importance in order to keep it aerobatic.


Remember, the BEC supplies power to the RX,
not vice versa. But the RX does turn on/control the power to the motor, therefore we would need to be able to activate the motor control line. I will think about that and maybe do a couple of tests when time permits.

There have been some good papers/threads on using infrared controls. The weight might be prohibitive for you. What is the total weight of your C/L plane, RTF? Nice plane. The wing concept is a good approach to reducing the weight.

I also have built a Speed 400 C/L. See my thread in this forum. Mine comes in a little heavy at 26 or so ounces RTF, but part of that is the RC throttle. I will reduce the weight on the next pass design. Will probably use some CF. The current design flies well but is not aerobatic with 6 cells.
Have not tested the 7 cells, but expect more speed and about the same maneuverability.

http://www.ezonemag.com/disc/smile.gif James

[Tapio]

How about using a RC speed control as motor cut-off? One needs to add some sort of pulse generator to switch the control on, any tiny microcontroller would to, maybe even some 555-based pulse generator. With microcontroller you could do all kinds of neat things, like a timer that enables you to arm the model and walk to the end of lines before power-up and start...

[steve lewin]

Originally posted by Tapio:
How about using a RC speed control as motor cut-off? One needs to add some sort of pulse generator to switch the control on, any tiny microcontroller would to, maybe even some 555-based pulse generator. With microcontroller you could do all kinds of neat things, like a timer that enables you to arm the model and walk to the end of lines before power-up and start...



You don't need a microcontroller to do that. I have a design I'm just testing which uses a CMOS 556 (twin 555s) to provide the intial "get to the handle" time as you describe plus a timed motor run. Mine drives the FETs directly so you don't need the ESC.

It would be very easy to convert it to drive an ESC which would then give you BEC-style motor cut-off and you could use the BEC to drive the timer. If anyone's interested in either version let me know and I'll publish the circuits.

The circuit you need to drive an ESC is just one of the many published designs for servo testers. Just take the pot out and fix it at either 1 or 2 ms pulses, whichever your ESC needs for full power.

Steve


[This message has been edited by slewin (edited 04-23-2001).]

[jrb]

Originally posted by slewin:
[b]
The circuit you need to drive an ESC is just one of the many published designs for servo testers. Just take the pot out ---

Steve



Has anyone taken the "pot out" to the contol handle?

[This message has been edited by jrb (edited 04-25-2001).]

[steve lewin]

Originally posted by jrb:
Has anyone taken the "pot out" to the contol handle?


That rang a loud bell. How's your memory jrb ? We were talking about that on one of the first threads in this forum. http://www.ezonemag.com/disc/Forum14/HTML/000003.html

You were there too.

Since then I've talked to Navy Carrier fliers who are using the same method to control the throttle servo on IC powered models.

Personally I'm still looking for a way to do it without needing bulky, draggy, insulated lines though. Thick insulated lines and small models don't seem to work too well.

Steve

[jrb]

Steve, memory is fine; just haven't read that anyone has done it yet.

"Carrier" is exactly what I'd like to try!

Also stil needs a 3rd wire (pot); but Larry @ SR suggested it could be done with 2? Could it be possible, thinking?

3 wires are just like normal IC throttle handle; servo must give more accurate/better throttle response since 3rd line doesn't need spring adjustment.

Have you looked at the plastic coated fishing line/cable? I guess it would be needed for larger models.

Can an S400 model use 22 to 18 gage insulated wire? ( http://www.geocities.com/CapeCanaveral/Cockpit/3188/flyinglines.html )

Looks like the old link as been updated -- a 7 chanel handle! ( http://www.geocities.com/CapeCanaveral/Cockpit/3188/electronics_main.html )

[jrb]

I looked at the 7 channel link; wow these guys are over the top! RC on strings.

All we really want to do is fly a little S400 ship and have full throttle control.

Servo tester with pot in handle would work' though I'm sure it needs to be 3 "draggy" wires.

Does a 1# model really need 30# test lines?

[steve lewin]

Originally posted by jrb:
Servo tester with pot in handle would work' though I'm sure it needs to be 3 "draggy" wires.


It only needs 2 wires. It's not really a potentiometer it's just a variable resistor i.e. one end is tied to the wiper. I'm not sure what lines you could get away with. All I've tried is 15lb test fishing leader. Unfortunately that's about .024" thick which is a lot for a poor little S400 to drag around.

I have to confess I was trying it with an IC motor and throttle servo. Those lines are less of a problem when you have a .19 diesel for power http://www.ezonemag.com/disc/smile.gif

[jrb]

Steve,

Guess it get down to the servo tester’s circuit.

Maybe you have a better one, but of the 5 listed here (I’m not sure if they all do the same thing or even what we want it to do), only number 2 uses the pot as a wiper resistor – 2 wires only.
http://www.uoguelph.ca/~antoon/gadgets/gadgets.htm
http://www.uoguelph.ca/~antoon/gadgets/servo2.htm

Please post a link if you have a better circuit; better yet I’d like to see this discussion in a separate posting so this good info can be easily found.

Also, does anybody know what type of pull test/line strength we would need for a 1# S400 model? Went to the AMA site and didn’t like seeing 20+Gs; but wouldn’t that be 10 Gs per line?

[broddarn]

Kyosho got one auto cut-off unit. It is an option for the parkflyer Ferias. Stock number 90511. It is not a controller, just a box that supplies the reciver from the motor battery. It have a safety devise, the motor won´t start before you push a button.

Gunnar.