DC motors wont run

Hi, I'm fairly new to Arduino and I'm having trouble running 4 dc gearbox motors that run at the same time. The motors say they run at 3V-6V which I am also confused on. I'm running the motors off a L293D motor shield that's powered with 4 AAA batteries that are 1.5V each. I mounted the shield on top of my Arduino UNO that's powered off a 9V battery. I removed the jumper off of the motor shield too. When I try running it with only 1 motor, it works fine. But when I try 2 or more, the motors are too slow to spin the wheel attached to them. Do I need to supply the shield with more voltage? If so, what would be a good source?

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You almost certainly need more voltage and also more powerful batteries than weedy little AAAs. Try 6 x AA NiMH rechargeable batteries which are able to supply much more current. The ancient inefficient L293D loses 2-3V of what you are supplying before it ever gets to the motors.

Steve

MoeMan: Hi, I'm fairly new to Arduino and I'm having trouble running 4 dc gearbox motors that run at the same time. The motors say they run at 3V-6V which I am also confused on. I'm running the motors off a L293D motor shield that's powered with 4 AAA batteries that are 1.5V each. I mounted the shield on top of my Arduino UNO that's powered off a 9V battery. I removed the jumper off of the motor shield too. When I try running it with only 1 motor, it works fine. But when I try 2 or more, the motors are too slow to spin the wheel attached to them. Do I need to supply the shield with more voltage? If so, what would be a good source?

The problem is your batteries cannot supply a high enough current. Motors use loads of current.

3V to 6V rating on the motor simply means they are rated for a maximum of 6V. All DC motors will run at lower voltages (proportionately slower).

Unfortunately the choice of L293D will compound the problems as it loses 2.5V or so from your 6V battery pack, leaving about 3.5V for the motors.

A better, MOSFET based H-bridge will allow full voltage to get to your motors, and a suitably uprated battery pack will provide enough current for all of them. A 2S LiFePO4 pack is one option (6.6V nominally), though you'll need the right charger to go with it.

6V SLA will work and have no problem with large currents.

4 NiMH D-cells of good quality will give 5.3V or so with good current capability.

BTW don't try to run multiple motors on each channel of a L293D, its struggling with one per channel frankly. Good MOSFET H-bridge is the way to go - checkout polulo.com for instance.

Thanks for the responses! I'm on a budget, so I am going to continue with the L293D. When looking at NiMH AA batteries, would I have to look at the current supplied by them or the voltage? The motors I'm using have a 1.2A stall so would that mean I would need 4.8A supplied to be 100% safe?

would that mean I would need 4.8A supplied to be 100% safe?

No, the L293D is a very wimpy driver, and can handle only 0.6A per channel, with a large voltage drop to boot.

It won't work well, or at all with your motors.

I'm on a budget, so I am going to continue with the L293D.

False economy. Skip that next cup of cappuccino and splurge $4.49 for this driver, which WILL work with your motors.

No, the L293D is a very wimpy driver and can handle only 0.6A per channel, with a large voltage drop to boot.

It won't work well, or at all with your motors. False economy. Skip that next cup of cappuccino and splurge $4.49 for this driver, which WILL work with your motors.

What is the best driver you do recommend to buy? I have no problem to spend money on a good-quality product. Just like the Launch x431 scanner https://bestobd2scanners.com/launch/x431-review/. It is a quality diagnostic scanner and works great. But, I bought a cheap scan tool under 100 bucks and it didn't support my car!

If you only need one motor direction (i.e. fwd/rev but not both) use a logic MOSFET for each motor.

Buy a DVM so you can monitor things like power supply droop and current draw.

MoeMan: Thanks for the responses! I'm on a budget, so I am going to continue with the L293D. When looking at NiMH AA batteries, would I have to look at the current supplied by them or the voltage? The motors I'm using have a 1.2A stall so would that mean I would need 4.8A supplied to be 100% safe?

Call it 6A so there's a decent overhead, yes. If the supply cannot supply the stall current in full its voltage will drop immediately, perhaps triggering the driver's under-voltage cutout.

Never skimp on power - if you need 2.5A, 3A is the bare minimum spec for the supply, 4A is much better. Its like car engines - if the red line is 6000rpm, don't drive it at 6000rpm!

What is the best driver you do recommend to buy? I have no problem to spend money on a good-quality product.

The one I linked should work fine and will handle two motors.

Pololu's drivers are of excellent quality, look through their selection.