Motor control (restriction : 2 x 1.5 volt battery)

[mickey]

Hi,

I have a project and I need to build a small vehicule with a source of only two AA bateries of 1,5 volt each. I want to control two diferents motors so I can go front back and turn (not more than that). Precision is not important so much, simplicity it is. I know that there is microcontroller but this is not my field of expertise. I just want to program my robot so it can goes front for 30 seconds than turn right, etc... Can I find servo motor running at 1.5 volt ?If you have any other suggestion at low price, I will very appreciate.

Thank you

[Razor Concepts]

You don't need to use a servo motor, just a plain old motor will do fine. Also, if you have two AA batteries at 1.5 volts each, why not put them in series to get 3 volts?

A very simple motor driver exists that can connect to a programmable microcontroller easily, the L293D or the new texax instruments one (7440 or something like that). Just look up l293d and youll find lots of circuits on it.

[mickey]

thank you, I will check

[colorclocks]

If simplicity is important, you can probably do without a motor controller altogether, and just use relays or transistors to switch the motor current.  You won't have speed control, so you'll have to choose motors that run at reasonable speeds on the voltages you have.

[mickey]

Is it complicated to make something like the Owi Binary Player Robot Kit (http://www.robotshop.ca/ProductSearch.aspx?qs=owi). In this case you can pre-determine the path of your robot. Any ideas in the same way...

thank you

[ghost]

If simplicity is important, you can probably do without a motor controller altogether, and just use relays or transistors to switch the motor current.  You won't have speed control, so you'll have to choose motors that run at reasonable speeds on the voltages you have.

Could I get more info on this please? 

I don't really understand how motors are controlled in r/c cars or robotics. 

[colorclocks]

If simplicity is important, you can probably do without a motor controller altogether, and just use relays or transistors to switch the motor current.  You won't have speed control, so you'll have to choose motors that run at reasonable speeds on the voltages you have.

Could I get more info on this please? 

I don't really understand how motors are controlled in r/c cars or robotics. 

If you just hook a motor up to a battery, without any motor controller in between, the motor will rotate at a speed that depends on the load its turning, and it will draw a current that depends on its speed.  If you're ok with this, then you might be able to get away without a motor controller.  You'll be able to make the motor go or not go, by disconnecting it.  You can make the motor go backwards by wiring it backwards.  (Not all motors are reversible, but all the DC motors I've come across are.)

So, if you're ok with just stop, forward, and reverse (i.e., you don't need to vary the speed), then you might be able to get away without a motor controller.  All you do is choose a motor and battery voltage so the motor naturally runs at a speed you can live with.  When the motor runs into tough going, its speed will decrease, and this speed decrease will cause the current it draws to increase, and the power that the motor delivers will increase as a result (up to a point).

This brings up one more important complication.  As I said, the current a motor draws depends on its speed.  Most motors will draw enough current to burn out their windings (melt insulation, cause a short circuit, and ruin the motor) if you increase their load sufficiently.  If you hold a motor's shaft still, while it's trying to turn, for example, and the battery is capable of supplying enough voltage and current to burn out the motor windings, then you will get a ruined motor.  This is because most motors have very low-resistance windings, and rely on motor speed to limit the current in their windings to a safe level.  (Motors act as generators, while they are turning, and the voltage they generate opposes the applied voltage, so the windings only see the average difference between the applied voltage and the generated voltage.)

You can avoid burning out a motor by ensuring that the motor never runs so slowly that it gets too hot, or you can use a weak enough battery that the motor won't burn out even if it stalls, or you can put a fuse or a circuit breaker in series with the motor, or you can get a motor with an internal temperature-based cut-off element.

Now, if you find you can, in fact, do without a motor controller, then you can put relays, or transistors, between the battery and the motor, and control the motor by controlling the relays or transistors.

[Admin]

1.5V you say? A lead-acid battery? You'll have trouble powering anything but weak DC motors with that.

Most motor drivers will require 3V or higher, but with a regulator you'd be lucky to get 2.8V on a microcontroller . . . assuming you can find a voltage regulator under 3.3V and above 1.8V . . .

That being said, you can probably build my $50 Robot without a voltage regulator and using a L298 motor driver, but . . . without a regulator funny stuff with happen so can't promise it will work . . .