Need help with design - electronics

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Timothy Huff
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Need help with design - electronics

Postby Timothy Huff » June 24th, 2018, 3:00 pm

I'm building two FN5 turrets at 1:4.5 scale. Each has:

A 12v/10w grain of wheat bulb - always on, operating at 12v

2 x 12v/5w grain of rice bulb - always on, one operating at 12v, the other at 4.5v

1 x 12v/5w grain of rice bulb, always on, operating at 9v.

3 12v/5w grain of rice bulbs, occasionally on, not more than 1/3 at a time, at 12v.

A 6v DC motor (possibly 2) of unknown wattage (https://www.faulhaber.com/fileadmin/Import/Media/EN_0615_S_FMM.pdf) to operate at 4.5v. This will drive a lead-screw/nut to elevate and depress the gun-cradle. Turret traverse will not be wired into this area.

Also entering the box will (presumeably) be 2 cables from the receiver to the motor, which is in effect a home-made servo.


Electronics are not my area of expertise at all. My intention is to run 5 cables from the top of the turret to the port ammunition box, with supplies of 12v, 9v, 4.5v and 3v, and a common earth, with a structure within the box containing little brass bus-bars ( a stock bar size from from K and S metals I would think) into which wiring from these various lamps and motors can draw current, with each protected by a TR5 fuse rated to circa 130% of the normal current draw for each service, perhaps mounted on a small PCB. The fuses I'm looking at are http://www.littelfuse.com/products/fuses/axial-radial-thru-hole-fuses/tr5-fuses.aspx.


If someone could let me know if I'm on the right lines, or if there's a more elegant way of achieving the same ends, I'd be most grateful. The volume into which everything would need to go is a box of 89x97x19 mm. A step-file of the precise volume is available on request. Any help most gratefully received!

Cary Bailey
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Re: Need help with design - electronics

Postby Cary Bailey » June 25th, 2018, 7:15 am

Not wanting to put a damper on things but your mixed voltages are going to be an issue here. Also the use of a "common earth" will also be a problem. First thing you need to do is find bulbs of a common voltage but also the current draw from your stated bulbs is quite high, can you not use LED's? You can get coloured LEDs that emulate the "glow" of a tungsten lamp.
That is what I would do as a starter and once you have that addressed your wiring will be a lot simpler, you would only need 1 battery & it would be a lot safer!
Cary

Steve Perry
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Re: Need help with design - electronics

Postby Steve Perry » June 26th, 2018, 6:03 pm

I vote for LEDs or fiber optic from one master bulb or LED.

If you really want to use traditional bulbs then the voltages that you looking for in your post are easy to deal with as regulators are available in 9 and 5 volt flavor, a 3s lipo will give you the 12 volts and power the other regulators. There is a sneaky trick to get the 3 volts, connect the 3 volt bulb between the 9 volt and the 12 volt :)

Regulator circuit https://www.eeweb.com/extreme-circuits/9-volt-2-ampere-dc-power-supply-circuit-diagram

The circuit for 5 volt is the same but with a 5 volt reg (7805) instead of the 9.

If you need more than 1.5 amps per regulator then it gets a little complicated and things start to get hot !

If we feed a 5 volt regulator on 12 volts then the missing 7 volts does not magically vanish, it generates heat.
pulling 5 amps that missing 7 volts gives ( volts X amps = Watts ) 35 Watts of heat !

Timothy Huff
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Re: Need help with design - electronics

Postby Timothy Huff » June 27th, 2018, 5:07 pm

Thanks for taking the time to reply so fully. The two brighter lamps - the spotlight and overhead lamp, are intended to illuminate the inside of the turret, in order to ease the depth-of-field issues for an FPV camera (when complete) trying to keep both the internal turret and exterior in focus and not "whiting out"/losing internal focus. By the time the FPV is installed - probably ten years from now, the technology may have overtaken the current depth of field issues, but I wanted to put provision for lighting just in case.

Reading up on what's been said here, I think the way to go will be to run all lamps at circa 5V, and to consider swapping out the two main illumination lamps (qv) with LED's at a later date. Once the fuselage airframe starts to go together I can see I'm going to have bring on-board an electronics whizz!

Steve Perry
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Re: Need help with design - electronics

Postby Steve Perry » June 28th, 2018, 7:46 pm

Have a look at fiber optics, something like https://www.ebay.co.uk/sch/i.html?_from=R40&_trksid=m570.l1313&_nkw=231917439525&_sacat=0 The 3mm end glow is 14 fibre optic strands each Ø 0.25mm with one brass ferrule (Ø3 x 15mm).


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