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Electronics tech Anything to do with the electronics in a model. Lights, Radio, ESC, Servo, Basic electrical.


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Old 11-11-2017, 01:12 AM
frizzen frizzen is offline
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Exclamation Remote LED control - for the back of the class

We could start with how servos work, pulse width modulation, how diodes work, electron flow theory... but your eyes are going to glaze over, or you'll go back to reading the Rc Car Action that's hidden behind your textbook. Yeah, I saw that.

Pre-requisites:
I have some leds I want to be able to turn on / off from my radio.
I have an extra channel to do it on.
I'm not afraid of a soldering iron.

1 servo
some 2.2k ohm resistors (2,200 ohms)
some resistors between 150 ohms and 600 ohms

We need a servo to die for this project. Any servo with a good board works even if you stripped the gears, or the potentiometer is bad. nothing to lose trying with a junk servo. My donor this time is a TowerPro SG90, because it's got a tiny board and I got 10 for $18.

*** don't order that servo yet, i'm having an overheat problem ***

Start off by ripping the servo open, pull the case screws, seperate everything and pull the board out. The pot can cause disassembly problems if they're screwed in place, or soldered captive. Some like my sg90 had the pot soldered in as an assembly step, so you have to grab some pliers and mangle the case until it lets go.



Leave the radio pigtail alone.
The pot can be replaced with a y bridge of 2.2k ohm resistors if you feel like it, or you can stay with the Pot for now if it still works.
to make the Y-Bridge remove the Pot, take a 2.2k resistor and solder it to where an outer leg of the pot was, solder the other leg to where center leg was, take another 2.2k resistor and solder where the center leg was, the other leg goes to *the other outer leg* of the pot was. It forms an M that connects where the pot went.
Solder a 150 to 400 ohm resistor to a motor pad or one of the wires that went to the motor,
solder the long leg of the LED to the resistor,
solder the short leg to the opposite motor pad.
Done.

Hook up your new creation to a channel in your rx that gives both throws to a servo, lights should come on in one of the not-center positions. tweak the pot to have lights off in center if you didn't make it a y-bridge. Cool, it works. Move it to a single throw channel, see if it still works, if not flip the led circuit at the motor pads.


Maybe i want to have one set of lights on, turn them off, and have another set turn on. (switch down - circuit 1, switch center - off, switch up - circuit 2) Wire circuit 1 one direction then circuit 2 opposite at the motor pads as the first circuit.


If you are working at normal RC reciever voltage(7.2v stick pack going into an ESC with a BEC for 4-6v output), a 150 ohm or greater RESITOR will safely get your LED working. Maybe you won't get peak output, but it gets your unknown lights scavanged off something going without freeing the smoke. Also no math.

If you are running red and white leds together like head & tail lights. Make a red circuit and a white circuit. the red need a bit higher resistance or the whites won't work. So my 150 ohm goes on the whites, red gets something 200-400 ohm to start with. play around with values before you finalize anything.
yellows need more power than red, less than white.
blue needs as much power as white (white is usually filtered blue)

If you over power an led, it will light up bright once for under a second, then never again.

try not to string too many leds into a parallel circuit, run a new resistor and wiring for them off the servo. I try to keep it around 10 or less, if you put too many in parallel they can start dimming out toward the end if the wire is high resistance. if you want to run series, it involves some math based on the forward voltage of the led adding together, and the voltage of your input. series lets you go without a resistor sometimes, but series without a resistor can also try really hard to kill batteries if it shorts.

Parallel is what I have mounted in the bumper. anode to anode to anode, cathode to cathode to cathode



Series is the row of 3 looking kinda like a WW. Boo this math!

I like micro servos since they break easy everybody has some scrap, are cheap, and someone you know has some broken ones. If you're going crazy with lights, use a bigger servo board since they work with more power. If you're going absolutely insane with lights, maybe that battle switch or a cheap esc is the way to go.


If you have LEDs or other components that have a long leg and short leg, the long one is + Positive. It's easy to remember that if you trimmed the legs even, it gives you a small piece that can lay over that leg so it looks like a + and the short leg doesn't have one so its still a -

the other way to tell polarity of a Light Emitting Diode is hold it up to a light, one leg goes to a big triangle, the other has a weird shape. big triangle is - negative.
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Last edited by frizzen; Today at 05:17 AM. Reason: Woo Post 600 was useful!!!
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