You are right. Also, the more information we could get, the better we could help Raul. A complete picture of what he has to work with, or exactly what he is trying to do, would be helpful. Brian
Didn't he say that the motor is a 6V motor?
Anyway, if the motor is made for 3-6 Volt it is probably not so wise to use 2*9V batteries. The voltage is too high and the current too low. Battery lifetime will be very short.
The best solution is to use 2*9V batteries for the op-amp, or use an op-amp which works well at 6V. (The 741 will work with just 6V but it will not work well. Limited range of output voltage)
And use the 2*3V for the motor. Those batteries last longer and are more suited for motors.
-- Roger J.
Ok, First let me say I really appreciate the help, a lot. The background information is that I am making a ROV. This motor controls the verticle movement of the ROV.
I live in Taiwan. I could go down to an electronics shop at 8pm on a Sunday, hand over the schematic, wait 10 minutes and pick up the finished circut. It would cost me about 2 dollars. But I don't really learn much from that.
When the whole thing is finished I will give to some engineers who will take my model and turn it into a well designed machine. For Chinese engineers, if I give them something, they can make it better. If I describe what I want, forget it. They're great at copying and improving. They're not good at inventing.
I'm also not set on anything. I have a bunch of motors, I don't care which one I use. The motor in the picture came from a 12v remote control car.
Someone mentioned the transistors were not that strong. I can change them, I just had those laying around.
I just need to control the the speed of a motor and have it reversible from one servo. The servo I can't change without going to a differen't RC system.
If I change that it means I have to go back and change a lot of stuff that already works.
That's the whole story... Let me say again, everyone has been great!
Raul
Your right, I could just but a new RC unit and do it that way, by skipping the servo, but in the unit I have, I have one free control and one free servo. In the unit I can't change out the servo for an electronic motor control without changing the reciever control board. So I want to control the pot with the remaining servo.
Raul
This is where I am now, The motor turns in one direction. I changed back from the 9v because the pot was always getting hot. The pot is
100ohm. Could that be the problem? RaulRaul, your 2N3904 transistor is plugged in backwards. The left pin of the
2N3904 (as pictured), is the emitter and the right pin is the collector. Just turn it around 180 degrees (if it hasn't been damaged), and it should work. The motor you are using right now, how much current does it draw? The 100 ohm pot. you are using, is much too small. 100 ohms at 18 volts will produce 3.24 watts of heat. The 10K pot. would only produce 0.0324 watts of heat. BrianIf you look at the hookup of the two transistors (to the right of the schematics), yes. If you look at the blown up pictures (of his wiring), when he turns around the 2N3904, then it will have the emitters together, to pin
2 and the motor. Brian
The pot has to provide very little current to the opamp so it can be a quite high resistance. A 100 k ohm pot would work fine and use very little battery current.
-- John Popelish
The transistor diagram still shows an emitter connected to a collector, instead of having the emitters connected together and to the motor and to pin 2. Each collector should connect to one of the supply rails.
-- John Popelish
I assume you intend to move the pot with a servo controlled by a radio control receiver unit.
This is a practical solution used by many, but it is an un-necessary transformation, to convert the received signal to be able to control a servo, then use the mechanical movement of a pot to convert the control signal back to an electrical signal.
It would be better to go directly from received radio signal to electrical control of the motor.
I don't have enough knowledge of the radio control scene but I am pretty sure there are receiver modules which convert to motor control directly, without using a servo to control the motor current.
If you do not want to use a readymade motor control unit you could build your own. Convert the servo control pulses into motor current directly.
If there is a need to keep size and weight down it is a bad solution to use a mechanical servo which is not necessary.
On the other hand, if size and weight are no problems and you want a quick solution the mechanical servo is maybe the answer.
(If you intend to use wire control instead of radio control this is still valid, I think.)
-- Roger J.
Okay, I just mentioned it in case you didn't know about direct motor control units.
-- Roger J.
I think the pot is 100 ohm. Not 100k. You can see it in the photo.
Raul
YES! I turned the 2N3904 around and it works! I also changed the 100ohm pot to a 100k pot and it works better. Next I'll try to find some stronger transistors to make it a little heartier. I've got some PN222's and some PN2907's. I think those are stronger. Thank you, Thank you, Thank you!!! Raul
I am recommending you change it to a 100k pot.
-- John Popelish
Well, here's the final product. Thanks again, it works great. Raul
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