Free Flight Electric ?

[JCastle]

I was thinking of adapting a Lite Stick motor with a Ray-o-Vac battery to a small vintage free flight plane. My question is what is a good way to set the motor up with a timer that will turn the motor off after a 10 or 15 second run. The plane was designed for a Cox .010. I found the plans in an old Molder Builder magazine and it looked like fun. Does anyone use electrics in free flight models? It seems that without the weight of servos and receivers it might work pretty well.


John

[andrewh]

John

Simplest F/F electric timer is an FET with a graduated leak. I have curcuit diagrams but essentially just a 5amp FET running the motor with a high value resistor connecting the gate to ground.

Before flight you charge gate using an external PP3 9V battery with adjustable voltage divider (so that you can set the voltage) this turns FET on. Voltage leaks away via resistor and when it gets down to the cut-off voltage the FET turns off.

If you are interested, I can probable dig out the article I have describing it. I havn't seen it on the Net, but it probably exists.

Alternative would be Tomy timer with micrioswitch.

andrew

[Terry Lyttle]

I have been experimenting with this for some years, and now have about a half-dozen models. Model Aviation ran a series of articles some time ago, demonstrating how versatile E-power is, including an inflight shot of a Dornier Do-X, freeflight!

My timing system has to do with battery capacity, ie, the smaller the battery, the less time it runs: you can run 6 50ma batteries for 30 sec, or 6 110mas for a minute and a bit.

At the moment I am working with the E-Charger toy system, but winter won't let go long enough for testing...

More fun than radio, simply because of the challenge.

[Bill Mixon]

Andrew,

I'd like some info on the system you mentioned above as well.

I'm looking for a cutoff timer that would work with 1 lithium polymer 3.7-4.2V cell powering a small brushed motor.

I'm surprised that some company isn't making something like this to sell.
The technology is there, I guess demand is too low.:rolleyes:

Thanks,
Bill

[T. Lyttle]

Yeah, that's part of it, but even freeflight timers are getting very difficult to find, again due to lack of demand.

The Tomy toy timers work fine, provided you get the right toy. I got one, and it zips off in about 3/4 of a second; wrong toy.

I have an old clockwork timer for fuel cutoff, great for short flights, maybe what is required.

I am converting a 50" Halibag to freeflight, but I am a long way from experimenting, and I am banging an experimental F9F together for a Hiline fan. Too many projects!

[Bill Mixon]

T.Lyttle

What toys have the tomy timer you mentioned?

I started another thread in modeling science, and it seems that there may be some units already being made for this purpose.

http://www.rcgroups.com/forums/showthread.php?threadid=185559&goto=newpost

I know what you mean by having too many projects
Thanks for the reply
Bill

[T. Lyttle]

I'm sure that there are circuits available for this job, seems I saw some a couple of years ago. Anyone with the ability to solder chips without blowing them should have no problem; Radio Scrap used to sell electronics handbooks, one of them was for the 555 chip, and I'm sure I saw timing circuits in there.

I am an electronic idiot, so I limit myself to wiring motors (only 2 ways, right and wrong, immediately noticeable), but most of you guys are way ahead of me!

[aeronutz]

Electonic timers for F/F
Its funny you shoudl ask ..... I have just made one of Andrew's timers. See pic. of it on the end of my finger
http://www.aeronutz.flyer.co.uk/MarkRCtimer.JPG
I am just writing an Aeronutz web page about this timer and a voltage switch that will stop the lithium cell going below 3v, liek when the plane is stuck in a tree!
The timer in the picture is for a small plane so it can be flown on a small field, one 145mA cell and a direct drive motor for silent flight. I think the plane woudl fly for about twenty minutes in one go so if you had 60 second motor runs then that would be ehh?? twenty flights before charging the cell up!
Its all really cheap too so take three planes ........
More soon

Mark
ps the timer in the picture runs from 0 to 90 seconds as you wish.

[Bill Mixon]

Nice,

How do you adjust the run time on that unit?

Bill

[aeronutz]

Adjusting the run time is really good ...... you charge the capacitor with a different voltage. This means the part inside the plane is simple and you adjust the part outside the plane. In thsi case we use a PP3 9V battery and a variable resistor and a voltage divider. Very cheap, very simple. So when the resisotor is half way along you get half the 9v and the timer runs for half of 1.5 minutes. I have done some test and stuff, I will do a web page on that shortly .......
The latest version of the timer is now much smaller and ligth er than the one in the picture !!
The Capacitor and resistor now fit between the pins on the transistor ! In the picture the transitor is the black blob at the top


Mark

[billystiltner]

Mark/Andrew
that is a clever little timer.
It opens up many possibilities for free flight electric.
Reducing battery weight meens we can fly smaller planes free flight electric. I guess it also meens we might loose some to thermals more easily. Thanks for sharing the timer.

I allready built a variable voltage supply from your(Mark) schematics.
I substituted 5k pot and 220ohm resistor. I also added a .1uF cap like on the LM317 package since I have mine located further than 6" from the filter caps. So far I have tested a few motors and I made a mini lathe of sorts. It's not really a lathe just a motor that I put balsa on the shaft then use sandpaper to turn it down.
Also I glued a dremel cutoff wheel to a gear and put on another motor. Now I can cut my music wire without aggravating the old lady. The motor is much quieter than the dremel tool. I guess I could have bought a dimmer switch for the dremel but I'm looking for some collets now.


Attached is one of the first things I made using the variable voltage power supply. A tiny bobbin intended for a tiny remote actuator.

Billy

[7homuz]

There is a section on electric freeflight on the Small flying arts forum.
www.smallflyingarts.com

Cheers, 7homuz

[Bill Mixon]

Good info.
thanks for the link, 7homuz

JMP in France (JMP Blackfoot) on these boards makes a custom timer unit. He is sending me one to try out. I'll post when I get it.

I know it would weigh more, but it would be nice to have a small pot on the timer itself for adjustment and a push button activation.
So that you would not need any other items while flying. Just set the timer push the button to start, and then after the flight push again to restart.

Bill

[Bill Mixon]

I've got my JMP timer and have been using it. It is very nice.

The timer can be set to run at times from 0 to six minutes. It has push button activation which also is used to program the time.:)
No need to have anything else to set it.
Also the power increases gradually during startup which serves two purposes well in my opinion...
1) it will be perfect for using on delicate geared motors (starts slowly vs. sudden full power)
2) you can release the button to set the amount of power for the flight vs. full power.
After a flight all you have to do is push the button again to restart.

The one I have is rated for 2.7-5.5 volts (single lipo) 2+ amp output.
On my scales it weighs .87 of a gram which is plenty light enough IMO.

Originally posted by billystiltner
Reducing battery weight meens we can fly smaller planes free flight electric. I guess it also meens we might loose some to thermals more easily.

JMP has a solution for this as well.
He can make a unit with two program modes. The first is to set the time and the next is for the DT actuator timer.

Bill

[Robbie d]

Billy,
I would be interested in hearing more about how you put together your lathe? Your bobbin looks pretty good by the way!
Happy building
rheannon