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Feb 05, 2019, 05:27 AM
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slowmatch's Avatar
I've just completed a video tutorial on how to build a Peterborough FET timer for our E20/Ferry 500 class:
https://www.youtube.com/playlist?lis...JEnNiYFZ7FNHRB

This shows the simplest version of the timer with an 8 second run but obviously the times can be altered to suit.
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May 21, 2019, 01:21 AM
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We've just added a new page to the Peterborough MFC for the Ferry 500 version of the timer. This is a basic 8-9 second version for use in the Ferry 500 class E20 featured in the June Aeromodeller: http://www.peterboroughmfc.org/Ferry500-Timer.html

Jon
Last edited by slowmatch; May 21, 2019 at 01:28 AM.
May 21, 2019, 05:54 PM
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Wondering if some other transistor or other component could be substituted to make a band burning or actuator DT? I suppose I could figure something out, but I'm not so great with electronics once I get past V=IR.

Maybe there's a normally closed virtual relay that's very light? Or a real one?

I suppose a battery or cap discharging through an actuator would eventually reach a low enough voltage that the actuator no longer applies any force. But that requires a very light actuator and, presumably, a much bigger capacitor. And it might not be as consistent.
May 22, 2019, 03:13 AM
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slowmatch's Avatar
Funnily enough I have been working on a capacitor based band burner DT
May 22, 2019, 10:15 AM
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Where does the trim pot go... If wanting a Variable timer?
May 22, 2019, 04:07 PM
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Hi Bare,

The trimpot replaces the resistor (R1) in the circuit below. The variable resistance being what changes the time.

The alternative is to build a 'zapper' with variable voltage to charge the capacitor.

We now have this index page which may help.

Jon



EDIT: The component's listed on the attachment below are for the 8-9 second Ferry 500 timer version. The diode D1 provides polarity protection and can be omitted as long as you are careful to only zap the correct positive/negative on the timer terminals.
Last edited by slowmatch; May 28, 2019 at 12:55 PM.
May 28, 2019, 10:48 AM
F8F
F8F
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The Peterborough timer initiates with a momentary charge delivered to the capacitor. There are certainly many ways this can be achieved. Have not researched other methods, but this quick proto works well and is very simple.

The ZAPPER (of which there and many configurations and could deserve a separate forum topic) can terminate in a probe made of a pair of thick, insulated, copper wires (2.5mm or US 12/14 gage). File both ends of the wire to an opposing taper. Trim off excess insulation. These become the “charged” contacts.
The timer can be assembled so the resistor wires, rather than trimmed short, can be formed into two parallel posts. The timer is then mounted inside the model with only the small “posts” projecting outside the fuselage. Be sure to color or mark the posts to identify the + and -.

Hold down the momentary “ON” button on the zapper and push the probe tip between the two posts. This momentary contact starts the timer.

BTW, have built 5 planes using the Peterborough timers, and all work perfectly. Really appreciate the full power for the set number of seconds, followed by the tapered motor shutoff. The planes gracefully transition from full climb to glide mode. Really recommend these devices for electric FF.
May 28, 2019, 10:58 AM
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Thank you... I had assumed as much. just wanting to be sure.
May 28, 2019, 01:35 PM
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Glad you are having fun with them Gregg

Quote:
Originally Posted by F8F
... Really appreciate the full power for the set number of seconds, followed by the tapered motor shutoff. The planes gracefully transition from full climb to glide mode. ...
It's probably worth explaining the 'tapered motor shut off' (also known as 'ramp down' or 'decay') for those who have yet to experiment with the timer. The decay occurs as the capacitor voltage drops through the 'gate threshold voltage' region of the FET. For the STD12NF06L MOSFET this threshold is about 2-2.5 Volts. At voltage drops from 2.5 to 2 Volts, the resistance in the FET increases until it shuts off completely.

The discharge of the capacitor is a curve as shown in the attached graph. If the FET threshold voltage is very low the capacitor voltage is dropping slowly at this point and you get a longer decay. MOSFET Gate Threshold voltage is found in the datasheets as VGS(TH) usually an approximation or a min/max figure is given. The proportion of decay time depends on the FET used, the voltage and the resitor/capacitor.

The most important thing to note practically, is that the decay time is a proportion of the total time so when using a trimpot to increase resistance for adjustment a 10 second run might have a 1 second decay but a 100 second run will likely have a 10 second ramp down.

The decay can be removed entirely by adding a few more components to the circuit if required. This is useful in competitions with a limited motor run time, especially with coreless motors that dwindle on and on at low voltages.


A rough calculation of the run time is possible as shown on the attached diagram. If you are using the STD12NF06L FET :

[Farads x Ohms x 1.5 = Motor run in seconds]

will get you close.


There are literally hundreds of FET's that would do the job, it's just that the STD12NF06L is well documented. A smaller SOT223 package FET and a B-case cap is my preference where weight matters.

Bare - a 33uF cap and a 1M pot will give you about 50 seconds max on a 9V zap.


Jon
May 29, 2019, 10:46 AM
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Quote:
Originally Posted by slowmatch
Glad you are having fun with them Gregg

There are literally hundreds of FET's that would do the job, it's just that the STD12NF06L is well documented. A smaller SOT223 package FET and a B-case cap is my preference where weight matters.

Bare - a 33uF cap and a 1M pot will give you about 50 seconds max on a 9V zap.


Jon
Soooo how long a run would this lil rascal allow ? https://www.sparkfun.com/products/746
May 29, 2019, 03:28 PM
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slowmatch's Avatar
Ha - that baby would power the model. No lipo needed!
May 29, 2019, 05:13 PM
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You might not get a run at all, since it's not rated for 9V. However, if you had 4 in series, that ought to last a month and a half. BIG Lipo and tiny motor required. I can't chase that far. Can you? ;-)
May 30, 2019, 06:20 PM
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Quote:
Originally Posted by slowmatch
Ha - that baby would power the model. No lipo needed!
That's what I was wondering. Fit the cap as the Lipo upgrade/replacement.
A teeny 1 s motor with small a draws might have several hours or more's duration.
It is rated at 3 A... more than most FF models motor's could require.
Plus there are even larger higher capacity versions available
Might even run a basic RC setup (if paired?) but haven't sufficient knowledge to actually know if it could be done.
Will try asking in DLG forum ... those guys are always looking for lighter power sources
Last edited by Bare; May 30, 2019 at 06:32 PM.
May 31, 2019, 02:51 AM
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Using super caps as a power source for small models is well established. They are not an upgrade on lipo though. Due to the non-linear discharge curve the thrust continually drops away from it's initial maximum, much like a rubber motor. In fact the power to weight and duration is similar to rubber flying.

At small sizes a super cap is probably equivalent weight to a tiny lipo but with lower voltage. Higher voltage super caps tend to be quite heavy so as model size increases they become less viable. But a small model can cruise about nicely for a minute or two with a small coreless motor.

Lots of stuff on the Hip Pocket Aeronautic forum about them and you can buy some small kits/toys too. Ebay is quite cheap to buy the standard 2.7V 5F or 10F sizes.
May 31, 2019, 03:36 AM
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Bare: DLG guys would probably like something that lasts an hour or more. You're not going to get that from a capacitor, but a lipo that weighs several grams can do the job.

With FF, you generally only need current for a very short time, which is more suited to the capacitor.


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