Could use help with a project.

[lstrike]

Hi.

I am building a remote-control tank for a project for school. Two of the main components I am using to build the tank's circuitry are a Picaxe 14M2 microcontroller and a Tamiya Double Gearbox. The issue I'm having is that the Picaxe 14M2 and most of the circuitry can operate safely at 4.5 volts, but the motors that came with my Tamiya Double Gearbox(FA-130 type) can only operate at 3 volts.

I'd like to know how I can get the Picaxe 14M2 chip to communicate with the 3V motors without killing them.

Thanks!

-lstrike

 

[techElder]

Istrike, you could use a separate battery pack for each. Use (2) "D" size cells for the motor supply and (3) "AA" size cells for the PICAXE. The COMMON (-) of the two batteries must be connected together.

Your PICAXE shouldn't be driving the motors, anyway. You should use a DRIVER between them. Perhaps an NPN transistor.

You should use a transistor between the PICAXE and the motor. The connection with a transistor is not complicated, but it has details. One detail is that the motor is connected to the 3 volt positive on one end with the other end connected to the COLLECTOR of an NPN transistor. The EMITTER of the NPN transistor is connected to the COMMON. The BASE of the transistor is connected to the PICAXE output pin THROUGH a RESISTOR. The RESISTOR value should be somewhere between 470 ohms and 1K ohms. (Experiment here.)

Create a schematic and upload it, so we can see what you have in mind.

 

[Bill.b]

I have built a rover using the same motor / gearbox and ran it a 6v with no problems.

Also I would use a L293D to drive the motors. this would allow you to run the motors in forward or reverse.





Bill

 

[geoff07]

Doesn't the M2 series run on voltages down to 1.8v?

http://www.picaxe.com/docs/picaxem2.pdf

 

[westaust55]

We need to know what other hardware is being used that cannot operate below 4.5 volts.
As already mentioned, the PICAXE chips can operate at lower voltages (but may not at upper clock speeds).

What interface do you already have,if any, between the PICAXE and motors.
What is the current rating of the motors. Do you need to reverse the motor direction?

If using PWM as opposed to continuous "on" state to drive the motors you may consider L293D chips for motors up to 600 mA which need a min 4.5V to the logic and motor supplies.

More information on your hardware will help receive better information.

 

[Goeytex]

I'd like to know how I can get the Picaxe 14M2 chip to communicate with the 3V motors without killing them.

This question suggests the understanding that the Picaxe 14M2 will somehow directly drive the motors. It cannot and should not in a proper design. In a proper design, the Picaxe will send a logic signal to other circuitry that will drive the motors at whatever voltage is required.

Manual 3 shows how to interface a Picaxe with other devices. Section 3 covers motors. See Page 13. Take the time to read/study the manual.

Since the tank will need to operate in both forward and reverse, the circuit on Page 13 using the L293D driver is probably is the way to go. The L293D will operate down to 4.5v (3 volts is too low). So the motors will be over driven by 1.5v. This should not hurt them much but may reduce operational life.

My suggestion is to get replacement motors that can operate at above 3.0V.

http://www.pololu.com/product/1117

 

[hippy]

The L293D will operate down to 4.5v (3 volts is too low). So the motors will be over driven by 1.5v. This should not hurt them much but may reduce operational life.

The L293D datasheet seems to indicate there is some voltage drop from what is supplied on VCC2 to what is delivered to the motors. That seems to be 2.6V as I read it so a 3V motor on a 4.5V supply should be safe to use and with a 6V supply not much over voltage.