Is it possible to use a capacitor in place of a battery to power a BS2 and 1 mi

Capt. Quirk

I have heared of people doing it with rockets and free flights, but I can't seem to find any information on the web to help me?

My intrest is for an F1J free flight with VIT and Bunt, controlled by a light weight servo and a BS1 or 2. Instead of using a mechanical timer.

Thanks

Bill

Bean

Bill,
How long does the BS1 or 2 and the servo need to be powered ?
Also I have no idea what "F1J", "VIT" and "Bunt" are. So I have no idea what you're talking about ???

Bean

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CCraig

I bought some super caps from AllElectronics. They are cool and will light a LED for a long, long time, and power a RTC for days..BUT...

Unless you just need a couple of pulses, I think you would be better off with a small battery.

HTH, Chris

Mike Green

Servos, even micro servos, tend to eat up power. An LED will put out light with only a few milliamps. A RTC takes microamps at most. A servo takes at least hundreds of milliamps. You should be able to run a Stamp off a super cap for more than long enough. You'll have to look carefully at the average and peak current draw of the servo as well as the expected movement profile to figure out whether a super cap would have enough capacity.

Capt. Quirk

Most of the functions happen within less than 10 seconds and then it will need to wait 3 to 6 min. for the·dethermalizer to kick in·and bring the plane down (the Free Flight dethermalizer, Rutan copied it for Space Ship 1).

The servo only needs to move about 1/4 of an inch or less and then wait, without any power (go to sleep)·until the next movement. It only needs to move about 4 times. Each time it moves to it's next position, it releases an wire arm and string that allows the conrol functions to occur. The engine kill, rudder and stab·move into a predeterined position. after the wire arm has been released, the arm and the string just hangs along the side of the fueslage until the flight is over.

In a contest, the plane climbs nearly straight up with a predetermined engine run time (aprox. 3 to 7 seconds) then the engine shuts down. shortly after that either the the rudder is adjusted or the BUNT (sudden down elevator) the plane goes into a circle pattern and the the elevator is adjust one more time for best glide ratio, until the dethermalizer kicks in.

I'll try to post some pictures later this afternoon.


Thanks

Bill
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Franklin

Seems to me a simple electronic timer would be more appropriate.

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- Stephen

Tom Walker

Also, keep in mind that for a servo to "hold" a position requires power. If you turn off the power to a servo, it just goes into a "free" mode without exerting any force on its moment arm, so there is nothing preventing whatever you have hooked to it from moving (except the system's internal friction, of course).· This could be accounted for by a mechanical system, but it should be noted...

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Truly Understand the Fundamentals and the Path will be so much easier...

Capt. Quirk

What voltage do·you think a super capacitor would need to charged to? 5v, 12v, 300v??

Paul Baker

Thats another issue to contend with, double layer electrolytics (super caps) typically are 2.5-2.7V max potential, so you would need to stack them in series to obtain a higher voltage (or find a super cap which does this internal), and capacitors are not like batteries, in that thier voltage is a function of thier capacity, so the more your deplete it, the more you drop in voltage (ie 2 2.7V supercaps will be >5V for only a very brief period of time). And you dont want to use a standard voltage regulator such as the one on the Basic stamp since it is highly inefficient. You would be best served by getting a very large value 2.7V supercap (10F or up), coupling that with a step up switching regulator, and feed the 5V output of the step up directly into the Vdd of your Stamp and also use it to supply your servo. Honestly, just using a couple coin cell·lithium batteries would be a much easier route.

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Paul Baker
Propeller Applications Engineer

Parallax, Inc.

Post Edited (Paul Baker (Parallax)) : 5/3/2007 9:57:41 PM GMT

Capt. Quirk

Thanks·everybody

Post Edited (Capt. Quirk) : 5/3/2007 11:19:44 PM GMT

Capt. Quirk

Here is what I trying to replace with an electronic timer and servo. The KSB is a
dethermalizer only for many size planes (but it's heavy and antique) The Selig multi-function timer is antique too, but it's a good example of what I am trying to do with the servo.

bobledoux

Put it together in a mockup. Your description suggests you could leave the servo powered down until a command is required, with each command moving the servo a bit further in rotation. There is no rotational force on the servo so there is no reason for it to move on its own, while powered down. There is a question of servo movement when it is first powered up.

I'm at a loss to suggest ways to create a low current release mechanism. A high current draw method is easy. Imagine, for example, the wire arm or string is attached by hot glue to a contact point. That contact point could be a model rocket motor ignitor. When it is fired the glue is melted and the wire arm or string is released. The problem is to create a release that doesn't use heat, which requires lots of current.

Dave Hein

Bill,

Does the plane have a battery to drive the propeller motor? Why not use that battery to run the controller and actuator? You may need to "condition" the power to the controller so it doesn't glitch, but I don't see why you can't use it. Of course, if the plane isn't electric powered you would need a battery to drive the electronics. I would use the lightest and most efficient battery you can find that has just enough energy to handle the flight duration.

If you use a capacitor to store energy you will probably need to devise a switching power supply to keep the output voltage at a constant level as the capacitor discharges.

Dave

Capt. Quirk

Bobledoux,
Your right about the servo, there will be no load on it when power is off. I was planing on using a vibra-tab as the switch. I'll put pressure on it and bend it until the model is released, the program can loop until there is a change in the Vibra-tabs value and then move on to the main routine.

Dave,
They are 1 cc nitro-methane engines, basicly a high powered Cox .049

Of the 4 pictures, 2 are the engine, 1 is the layout of a similar plane and the last gives you a good idea of how little space there is.

Bill

Post Edited (Capt. Quirk) : 5/4/2007 9:17:24 PM GMT

Dave Hein

I like the carbon fiber structures.· Even the folding prop appears to be carbon fiber!· As I mentioned, the optimal design would use the smallest battery or capacitor that can hold just enough energy for the flight.· This would require operating as the battery/capacitor voltage drops.· With a minimal amount of components, the processor could handle the switching power supply functions.· I would suggest using an SX instead of a BS1 or BS2.· This use less space, and probably less power.

I think the only way to know how much power is needed is to run a number of tests.· You may have to power the actuater during the ascent phase because of the acceleration forces during that time.· As you mentioned, you may be able to de-activate the power during the coast phase, except when the four changes are made.

The only way to know for sure is to test it.

Dave

Capt. Quirk

Dave,

I agree, the SX would work great for that application.

Now it's time to stop bench racing and get to work.