DC Motors, Low Torque, H-bridge Problem?

Other Hardware Motors, Mechanics, Power and CNC
1

In this project, I am driving two 6V 100 RPM N20 motors with a 6V DC power supply (4 AA batteries) and an L293D IC, controlled with a Pi Pico. To my frustration, I am not getting a lot of torque. The motors would stall all the time. It barely works with 50 or 60 RPM motors and it's of course much slower.

I have made something similar for another project with the same mechanics and the 6V 100 RPM N20 motors worked fine. The difference is that one used an L9110S breakout board like this.

I have switched mechanical parts of these two projects and it didn't change the results. So that ruled out the mechanical difference such as friction. I have also ruled the motors themselves. I have tried 3 pairs with the same result. Now, I suspect the H-bridge IC L293D I'm using does not provide enough current. Before reaching for the solder, I wonder if there's any merit in my suspicion. Or could there be other factors at play here?

Thanks.

Schematic:

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2
  • Isn’t there a Pi forum ?
3

I don't suppose the MCU is actually relevant, since it simply provides the logic control to the H bridge.

4

  • Always show us a good schematic of your proposed circuit.
    Show us good images of your ‘actual’ wiring.
    Give links to components.

  • The L293D is old technology, inefficient, overall poor choice from what’s available today.

5

Current is possible, but it wouldn't be my first guess. Voltage on the other hand...

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Running on a 6V power supply, the L293D will output at most 6 - 1.4 - 1.2 = 3.4V to your motors. Perhaps as little as 6 - 1.8 - 1.8 = 2.4V.

Something to think about while trying to use 6V motors.

6
  • Show us good images of your ‘actual’ wiring.
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6V into Vcc1? Why?

8

Is that a potential problem? The datasheet indicates that this is the logic power supply but it takes up to 36V.

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9

Just asking a question. If you don't see it as a problem, carry on.

10

Hmm, I didn't even notice the voltage drop. That's a good point. I suppose it uses bipolar transistors?

11

Yes there is.