Controlling a 4 wire servo

ebeowulf17

Joined Aug 12, 2014
3,307
Thanks for the offer, but I already found the solution, and I feel really stupid.
All you have to do is put grey and white into 5V and GND, depending on which you put where it steers in each direction.
But the important part is to use two different power sources for red/black and grey/white, or nothing happens.
So it does indeed look like I need a H bridge, but I wonder how I should organize 2 power sources, and which voltages they need...
Sweet! Nice job finding the basic control concept.

I know you said the remote to the control board doesn't work, but can you power it up at all? If you power it, do you see power on any of the wires that go to the servo? My guess based on what you've said so far is that you won't find any voltage between the white and grey wires, but if you're lucky, maybe you'll find some voltage on the red and black. If so, you'd be one step closer to picking voltages.
 

dendad

Joined Feb 20, 2016
4,452
It sounds like the NK2903H chip may be an H bridge.
Can you experiment with PWMing one input with the other at 0V or 5V?
 

ebeowulf17

Joined Aug 12, 2014
3,307
It sounds like the NK2903H chip may be an H bridge.
Can you experiment with PWMing one input with the other at 0V or 5V?
If it is an h-bridge, wouldn't there be risk of essentially creating a short circuit if both inputs are active at once, causing all switches on both sides of the bridge to all close at once?
 

Thread Starter

DQQpy

Joined Aug 31, 2017
17
Sweet! Nice job finding the basic control concept.

I know you said the remote to the control board doesn't work, but can you power it up at all? If you power it, do you see power on any of the wires that go to the servo? My guess based on what you've said so far is that you won't find any voltage between the white and grey wires, but if you're lucky, maybe you'll find some voltage on the red and black. If so, you'd be one step closer to picking voltages.
The remote is completely disassembled, and the resistances and capacitors of the PCB are ripped off. I guess I didn't like electronics when I was 5 :D
I'm pretty sure I need 6V on the red/black, because that's what in the car was, and it works fine. For the grey/white ones I slowly increased the voltage with a potentiometer, and at about 4.6V it turned, so I'll put the Arduino 5V on that.
It sounds like the NK2903H chip may be an H bridge.
Can you experiment with PWMing one input with the other at 0V or 5V?
Sure, I'll try it out in a moment. I'd like to stop the motor in the L/R steering position anyway, because it doesn't yet, it keeps pushing.
If it is an h-bridge, wouldn't there be risk of essentially creating a short circuit if both inputs are active at once, causing all switches on both sides of the bridge to all close at once?
I have pretty much tried every possible combination of 5V/GND on grey and white now, that one included
 

dendad

Joined Feb 20, 2016
4,452
If it is a "proper" H bridge, it will have internal gating to prevent all FETs??? on together.
You could put a 100R in series with the power, and remove the motor, adding a Red/Green reverse connected pair of LEDS (parallel, not series) with a 1K series resistor to make it safer to play with.
 

ebeowulf17

Joined Aug 12, 2014
3,307
If it is a "proper" H bridge, it will have internal gating to prevent all FETs??? on together.
You could put a 100R in series with the power, and remove the motor, adding a Red/Green reverse connected pair of LEDS (parallel, not series) with a 1K series resistor to make it safer to play with.
Ah, sorry. I read warnings all the time on this forum about shoot through when people are designing their own h-bridges. I didn't realize that "proper" ones have built in protection. That makes perfect sense.
 

ebeowulf17

Joined Aug 12, 2014
3,307
I guess I didn't like electronics when I was 5 :D
That's awesome! When you referred to "little me" earlier, I thought you were saying that you had a small child in the house who destroyed things - I didn't realize the small child was just you at some point in the past!
 

jayanthd

Joined Jul 4, 2015
945
The remote is completely disassembled, and the resistances and capacitors of the PCB are ripped off. I guess I didn't like electronics when I was 5 :D
I'm pretty sure I need 6V on the red/black, because that's what in the car was, and it works fine. For the grey/white ones I slowly increased the voltage with a potentiometer, and at about 4.6V it turned, so I'll put the Arduino 5V on that.

Sure, I'll try it out in a moment. I'd like to stop the motor in the L/R steering position anyway, because it doesn't yet, it keeps pushing.

I have pretty much tried every possible combination of 5V/GND on grey and white now, that one included
Don't connect Arduino 5V to Motor circuit. Motor needs more current. Arduino power regulator will heat up.
 

Thread Starter

DQQpy

Joined Aug 31, 2017
17
It sounds like the NK2903H chip may be an H bridge.
Can you experiment with PWMing one input with the other at 0V or 5V?
I tried to PWM fade one input on the whole spectrum from 0 to 255, with the other wire on 5V or GND. The motor turned on the higher values and went back on the lower, but with a humming noise the whole time. Both wires in 5V and GND of the Arduino just turned the motor without noise, as usual.
If it is a "proper" H bridge, it will have internal gating to prevent all FETs??? on together.
You could put a 100R in series with the power, and remove the motor, adding a Red/Green reverse connected pair of LEDS (parallel, not series) with a 1K series resistor to make it safer to play with.
I'm not sure if I understand your circuit correctly, but I think since I've figured out the basic control I don't need to play much more with it, right?
Don't connect Arduino 5V to Motor circuit. Motor needs more current. Arduino power regulator will heat up.
Yes, but my multimeter showed an amperage of 14mA while stalling, so it's safe. It seems to draw the major current off the red/black circuit.
 

ebeowulf17

Joined Aug 12, 2014
3,307
Don't connect Arduino 5V to Motor circuit. Motor needs more current. Arduino power regulator will heat up.
Pretty sure he means 5V Arduino signal on the grey and white external control wires, not the motor wires, then separate 6V on red/black to power the whole thing. Sounds right to me.
 

dendad

Joined Feb 20, 2016
4,452
I'm not sure if I understand your circuit correctly, but I think since I've figured out the basic control I don't need to play much more with it, right?
A very handy little bit of test gear is 2 x LEDS. Connect the RED LED anode to the GREEN LED Cathode, and connect the GREEN LED anode to the RED LED Cathode. Now put a 2K2 resistor onto 1 connection, then a wire on the other end of the resistor.
The other side of the LEDs , put another wire.
Heatshrink the connections. Now you have a test lead that will light RED or GREEN depending on the polarity. and YELLOW (sort off) on AC.
You can just use a BiColour LED that has a RED and GREEN LED in the one package, connected as above. It is a 2 wire package, not 3 wire.
http://www.mouser.com/ds/2/244/SSL-LX5093IGW-1137432.pdf

This is a good replacement for the motor as you can see the current direction change.
I use a RED and GREEN wire, connected so +ve on the wire colour lights that colour LED.

I tried to PWM fade one input on the whole spectrum from 0 to 255, with the other wire on 5V or GND. The motor turned on the higher values and went back on the lower, but with a humming noise the whole time. Both wires in 5V and GND of the Arduino just turned the motor without noise, as usual.
The humming noise would be the PWM signal. It looks like you have worked it out :)
And yes, the RED and BLACK will be the power to the motor so it will draw the main current. the 14mA would only be the control current I think. The motor stall current will be a lot higher, and the Arduino reg would probably have a little trouble with that.
 
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