This is progress. It sounds like the transistors are working fine. It is something with your receiver itself, or with the wiring to your receiver.
Double-check your connections with a multimeter. See if there is a short between your receiver outputs while it is disconnected from the transistors. If you find no short, re-connect it and check for a short between the receiver outputs again.
Also try disconnecting your receiver and testing the outputs while you send commands from your transmitter. Verify that receiver output 2 is inactive when you are only commanding output 1 to turn on, and vice-versa.
Here are the readings I am getting from my meter with the 4 wires disconnected from the receiver to the circuit.
From the receiver there is a battery connection, and additionally two red wires, a yellow wire and a blue wire.
I connected the battery, thenI attached my meter from 1 red wire to the yellow wire, when I turned the left control stick on the transmitter (that would run both motors), the voltage would be around 5.16V. Then turning the right control stick on the transmitter (that would run one motor), in one direction, the voltage reading was 5.06V, then turning the right control stick on the transmitter the opposite direction, the voltage was 0.
Then I attached the same red wire to the blue wire, and followed exactly the same procedure. The left control stick (for both motors) was the same around 5.16V. However when turning the right control stick on the transmitter (that would run one motor), I got just the opposite results as I did before, as anticipated.
Then, using the other red wire, I followed the same procedure and got the same results.
Sorry, maybe I’m a bit slow this morning. I’m having trouble understanding your description.
Maybe a picture of your actual receiver and transmitter would help. Or model numbers so we can look them up.
My limited experience with RC receivers is that each channel has a three pin connection (power, ground, signal), typically used for running a servo. There’s sometimes a separate three pin connector that lets you connect power and ground input for the receiver, but I’ve also seen some where you use one of the servo connectors to provide power and ground for the receiver itself too.
Your drawing is very different from the above. It would help to understand what your equipment is.
I almost think the red wires are constant +, could you check this?
If so…it explains all: The motors then are controlled by switching the negative wire. This explains why they both run when connecting to 1 battery. In that case you should need PNP transistors instead of the NPN you’re using now with a slightly different circuit.
What I have is called a yellow bee RC airplane, they are sold though Harbor Freight.
They are a cheapie.
It uses an airplane transmitter with a control stick on the left that moves up and down. The movement up does nothing but when you move the stick toward you (down) then both small motors run.
On the right of the transmitter a control stick moves to the right and left. Moving the stick to the right, will operate the right motor. Moving the stick to the left, will operate the left motor.
When I dismantled the receiver and motors, from the airplane, the receiver has two wires going to each motor. A red wire, and a blue wire to one motor, and a red wire and a yellow wire to the other motor. It has a 6V battery pack (using 4 recharageable AA batteries in a shrink wrap, I would guess) to power the receiver and the 2 small motors.
It was using a servo motor amp board. Since this airplane receiver did not have a servo motor amp board, I just tried to modify it to work for my larger motors and using 12V.
Finally, I discovered that by using the schematic that I posted originally, I could get it to operate either motor independently, or both at the same time if I used 2 power sources. Thus coming up with the schematic. This circuit does work, but I am simply trying to eliminate one battery if possible.
OK, so it sounds like Dannyv is correct, and the red wires are just 5V power and are on all the time. So the yellow and blue wires are your signal that you need your circuit to respond to.
Measuring from the receiver ground for all measurements, can you tell us the voltage on:
yellow wire when the receiver is off
yellow wire with the receiver on and the control in neutral position
yellow wire with the receiver on and the control in the “on” position
blue wire when the receiver is off
blue wire with the receiver on and the control in neutral position
blue wire with the receiver on and the control in the “on” position
Assuming the yellow and blue are your signal outputs for channel 1 and channel two, if they are active high, you should see them at about 5V when you command them “on”, If they are active low, you should seem them at about 0V when you command them on.
Assuming they are active high, your circuit will work when you make the following connection changes:
Disconnect both red wires. You don’t need them
Disconnect the yellow wire from the emitter and 12v battery ground; connect it to the input of the base resistor.
Disconnect the blue wire from the emitter and 12v battery ground; connect it to the input of the base resistor.
If your signal wires are actually active low, you will need to replace your transistors with PNP style components.
Now with my red lead of my meter on the + battery terminal, here are the results:
When the receiver is off and the black lead of my meter attached to either the blue, yellow, or 2 reds, I get 0V
When the receiver is on and the black lead of my meter attached to either the blue, yellow, or 2 reds, I also get 0V.
With the transmitter turned on and in neutral, and the receiver is on, I get 0V on each of the wires as well.
With the transmitter turned on and the stick that controls both motors is on, I get 0V on both reds, and I get 4.98V on both the blue and yellow wires.
With the transmitter turned on the the stick that controls each motor independently is on, I get 0V on both reds, whether I turn the stick to the right or left. When I move the stick to the right I get 4.98V on the yellow wire and when I move the stick to the left I get 0V on the yellow wire. Conversly, when I move the stick to the left I get 4.98V on the blue wire and when I move the stick to th right I get 0V on the blue wire.
OK. So it sounds to me like your receiver provides an active LOW signal on the blue and yellow wires. You cannot trigger an NPN transistor with an active LOW signal.
You do have some choices.
You can replace the current NPN power transistors with PNP power transistors
You can keep the current NPN power transistors, but get a pair of small general purpose PNP transistors to drive them.
Just about any general purpose PNP transitors should be OK. You are just using them to switch the power NPN transistors.
The 10k pull-down resistors keep the NPN transistors off, unless the general purpose PNP transistors are turned on by the active LOW signals from the yellow or red wires.
A diode parrallel over the motor is recommended… placed with anode to -. When a DC-motor is turned off it could give some current back to the transistor (it’s a coil) wich can kill the transistor. the diode should be fast and strong enough depending on your motor…
Many thanks to ignoblegnome and Dannyv. It uses 1 battery just like the schematic. I used a pair of MPS 4126s. PNP general purpose transistors I had laying around, a diode across the motors and it works great.
Thanks for sticking with me. I hope I can help sometime. You guys are tops.
Since my grandson crashed the cheap harbor freight airplane one too many times, we are going to work together since we salvaged the receiver, and put some wheels on some kind of 3 wheel device and keep the controlling on the ground instead of the air.
I have looked through the LMR website, and it is truely amazing the things that you guys come up with.
THAT would be a cool video for youtube 