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Author Topic: Trimming capacitor powered model  (Read 675 times)
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Glidiator
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« on: June 10, 2018, 10:46:08 AM »

Hi,
Could not find a specific section for indoor capacitor powered models hence posted it here
Have made the Cap Basic model
How does one go about trimming a cap model
In rubber one can gradually increase turns/torque or use half motor or use a spacer stick to reduce rubber etc so it gives short flights to assess performance and trim

So in Capacitor power does one start with say 15 sec charge and then increase charging time gradually while adjusting trim so it does not climb and get stuck in the rafters

or is there a tried and tested method

Anant
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ghcrash
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« Reply #1 on: June 10, 2018, 11:12:55 AM »


I've been playing with indoor capacitor free flight plane for a couple of years and the only way I know is what you suggest, start with a partial charge and work up from there.  But counting seconds never worked very well for me.  Capacitors charge rapidly and it is hard to get a consistent charge from one flight to the next.

You might want to invest is a small adjustable voltage regulator and then charge the capacitor to a specific voltage.  The picture is of my voltage regulator taped on top of a 2s Lipo which is the power source.  The regulator was about $5 on eBay.
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Glidiator
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« Reply #2 on: June 10, 2018, 11:30:25 AM »

Hi,
Thanks for your inputs

That voltage regulator seems a good reliable method
Something like a rubber torque meter so you know what exactly is happening in terms of power available

But I feel what is important in cap power is to charge it sufficiently to get max rpm on motor as rpm drops as charge reduces so you know what the model does at max rpm
Then with more charge the duration of max rpm increases
So one can aim for a long max rpm period and trim so it does not keep climbing and hit the rafters and instead goes to appropriate height and keeps cruising at that height as long as max rpm persists

Anant
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Glidiator
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« Reply #3 on: June 10, 2018, 11:48:10 AM »

Hi,

Can you give me the Ebay link for the voltage regulator

Thanks
Anant
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ghcrash
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« Reply #4 on: June 10, 2018, 12:51:12 PM »


Max rpm is dependent on capacitor charge.   So max power, or rpm will be less at half charge than at full charge.  And that max power will be at the very beginning of the flight with power and rpm decreasing almost linearly from there.  All this is old news to everyone.   Trimming the plane for a slow, or no climb, at max power may (probably) give you a plane that dives at some low-power point in the flight.  (Try lots of down thrust to prevent that)

There are two basic approaches to capacitor free flights.  The most common is to use a motor and prop combination the gives a rapid high climb with the plane transitioning to a glider as the capacitor drains.  The other approach is to use a prop-motor combination that gives a very slow climb at full charge and a slow decent as the capacitor nears empty.  I use the second method as the indoor site I use has a 23 foot ceiling.  My primary capacitor plane uses a 8 farad capacitor, 6mm can motor with a 25:1 reduction gear swinging and a 11" diameter prop.  Flight profiles are similar to an EasyB rubber duration.

This is like  the step-down DC-DC regulator I presently have.  https://www.ebay.com/itm/Adjustable-DC-DC-LM-2596-Converter-Buck-Step-Down-Regulator-Power-Module-/273040330884?_trksid=p2349526.m4383.l4275.c10#viTabs_0
But I may get this one.   https://www.ebay.com/itm/DC-DC-Step-Down-Power-Supply-Adjustable-5-23V-To-0-16-5V-Buck-Converter-LCD/202235328772?hash=item2f162a3904:g:h3AAAOSwtDdajMyr

Any adjustable DC to DC step down converter (regulator) will work.  Pick one with a reasonable input voltage range, a low(<5v) out put range with a good accurate readout.
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raggedflyer
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« Reply #5 on: June 10, 2018, 01:13:53 PM »

You might try the very old trick of fitting the propeller on backwards to run less efficiently if that is possible, which would allow a higher voltage charge and higher rpm to be used but with less thrust.
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Glidiator
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« Reply #6 on: June 10, 2018, 08:57:41 PM »

Hi,
Have ordered the voltage regulator. Just $2.79 on Ebay and free shipping too.
Need to know how to hook it up between battery and capacitor.
Anant
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Glidiator
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« Reply #7 on: June 10, 2018, 10:53:05 PM »

I have fitted a 10F capacitor.
Prop is 120mm and there is a reduction gearing.
Very short test flight in drawing room with minimum 10 sec charge showed a slow climbing flight before it hit the wall.
Don't want to risk damage so will do further testing in larger indoor space where Ugly rubber Power.
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Glidiator
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« Reply #8 on: June 10, 2018, 10:55:23 PM »

Sorry for auto correct
Ugly = I fly
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ghcrash
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« Reply #9 on: June 10, 2018, 11:18:05 PM »


Very short test flight in drawing room with minimum 10 sec charge showed a slow climbing flight before it hit the wall.

Ten seconds is a long time to charge a  capacitor unless there is a resistor on, or resistance in, the capacitor's charging circuit.  Two to five seconds is all it should take to charge the capacitor to 90% of its rated voltage with a low resistance charging setup. 

B y the way, what voltage are you charging with, what are you using to supply the charge current? 
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Glidiator
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« Reply #10 on: June 11, 2018, 01:09:48 AM »

I am using a charging box that holds 2 batteries of 1.5 V each. The resistor terminals just insert into the female socket of this box conviently.
This came with a cheap Chinese capacitor model.
This readymade model needed a 1 min charge to reach max rpm and sustain for about a minute. Have noticed that even my 10F capacitor gives max sustained rpm after about 30 sec charge So I guess my charging voltage and amperage are pretty low so it takes longer to give adequate charge.
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frash
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« Reply #11 on: June 11, 2018, 05:16:39 PM »

ghcrash,

Thanks for the charger recommendations.  Today I ordered the second "buck charger" that you recommended.

Recently I flew  a Chuck Markos' Science Olympiad Capacitor Wright Stuff design in a site with lower ceiling than usual and used only a 4-second charge. This particular plane is overpowered with 7-mm motor, 65-mm TriTurbo prop and no gearing. Your prop and gearing seems considerably better.

Markos' plan in Plans section below:
http://www.hippocketaeronautics.com/hpa_plans/details.php?image_id=9801

Fred Rash
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Glidiator
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« Reply #12 on: June 15, 2018, 12:47:56 PM »

Some pics of my Cap Basic model
The wing and stab film is  8 micron film.
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frash
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« Reply #13 on: June 20, 2018, 05:39:31 PM »

Glidiator,

Your Cap Basic model looks like it will fly well.  The geared motor is something that I should adopt instead of only trying it occasionally.

Ghcrash,

The Buck converter charger arrived and has been bench tested, but not actually flight tested. I had 9-volt batteries and wiring clips to fit into the left side Vin and GND terminals. The right side or output terminal wires required soldering on SIL connectors to mate with the SIL connectors on my capacitors.
The display is large and well lit.

I charged a 10-Farad and a 6-F capacitor up to 4V and quickly disconnected from the capacitor.  (I had read a report from Germany that the 2.7V caps could be charged to 4V.)  The 6-F capacitor got rather warm.  The 10-F cap was discharged to a 7-mm motor with TriTurbo prop and seemed to show somewhat  faster RPM and longer duration of power.

Surprisingly, the charging current was as high as 2.5 amps for a second or two.

DC-DC Step-Down Power Supply Adjustable 5-23V To 0-16.5V Buck Converter + LCD

Fred Rash
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Glidiator
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« Reply #14 on: June 21, 2018, 02:40:57 AM »

Will test fly the model soon.
Have also ordered the voltage regulator for charging. Await its delivery.

 Reduction gearing available on EBay at $3.79 -- free shipping from China

https://www.ebay.com/itm/720-Deceleration-Group-DIY-Fixed-Wing-Aircraft-Module-Reduction-Motor/392011217560?hash=item5b45b07a98:g:ZL8AAOSwpWBawJe1

Anant
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ghcrash
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« Reply #15 on: June 21, 2018, 06:44:55 AM »


I charged a 10-Farad and a 6-F capacitor up to 4V and quickly disconnected from the capacitor.  (I had read a report from Germany that the 2.7V caps could be charged to 4V.)  The 6-F capacitor got rather warm. 

Surprisingly, the charging current was as high as 2.5 amps for a second or two.

Fred Rash


Like you I charge my 2.7v capacitors to 3.5 to 4 volts.  Almost all of the super capacitors will stand some over voltage charging.   The downside is that the more they are overcharged, both voltage wise and frequency, the more likely they are to fail.  And as you saw, the charging current can be pretty high.   

A low ohm resistor could be installed on the capacitor side of the voltage regulator to reduce the initial high current.  It would also help  in minimizing heating of the capacitor during charging.   

   George
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Glidiator
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« Reply #16 on: July 10, 2018, 07:33:38 AM »

Hi,
Just received the charging converter today.
Need to put it into action and learn how to connect it up.
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ghcrash
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« Reply #17 on: July 10, 2018, 02:59:47 PM »

Just received the charging converter today.
Need to put it into action and learn how to connect it up.

It's simple, Anant.    Your voltage regulator looks just like mine except for the color of the circuit board. 

 All the terminals are marked.  I use a 850mah 2s lipo for my voltage source but anything between 5v and 15v will work fine.  A 9v alkaline battery would be perfect but almost anything will work.   I do suggest a switch or connector between the battery and the voltage regulator so the regulator can be completely powered down between flying sessions.  I just use the standard JST battery connection on mine.  There is a small push button switch just to the left of the display that I think is suppose to be an on-off switch but I had my 2s lipo drained one time when I used it and didn't unplug the battery.    The small push button switch to the right of the voltage display allows you to read either the input voltage or the output voltage.  Adjustment of the output voltage is by the tiny brass screw in the blue block above the display.   My fingernail just fits the slot in the screw.   The adjustment on my voltage regulator is not very  precise but I understand that the output adjustment on some of the voltage regulators can be sensitive to the input voltage.

Use whatever you have for output wiring.   I use some 26ga wire that I had laying around but even 32ga would work.  I made the output wiring fairly long, 10-12 inches, so that I could leave the regulator and its battery in my shirt pocket while charging the capacitor.   (I usually make several flights at the same voltage before making any changes and it is a lot easier to not have to hang on to the regulator at the same time you are trying to connect it to the capacitor.)    Voltage adjustment is done prior to charging the capacitor.   I don't use a resistor in the output wiring, nothing wrong with a low resistor, it just slows down the charge rate.  I do wait 3-5 seconds after the voltage reading has stabilized before disconnecting the capacitor from the regulator.
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Glidiator
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« Reply #18 on: July 10, 2018, 04:05:23 PM »

Thanks ghcrash.
That explanation on hooking up the voltage regulator was very clear.
Will hook it up and report results
Anant
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Glidiator
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« Reply #19 on: July 10, 2018, 04:12:25 PM »

Do you also have a switch between capacitor and motor. As the prop will start rotating as soon as enough change comes into the capacitor.
Anant
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