L293D motor shield with RC car

Hi all,

I have this old RC car I found (it’s around 20 years old). I ripped out all the inside electronics and left the dc motors in place. I can power the dc motor using my uno (powered by a usb power bank) and 8 AA batteries in parallel reading at about 10 V (4 are rechargable, 4 are not) are powering the L293D motor shield. I connected motor 1 pins to the dc motor and managed to get the wheels moving, but then as soon as I put the car down on the ground it doesn’t get enough torque to push the car. So I then thought I’ll use the motor 1 and motor 2 pins in parallel to power the dc motor, as maybe the current wasn’t high enough. I can now occasionally get it to drive the car, but sometimes it just doesn’t (and when that happens, the L293D IC gets hot to touch).

I then did a quick test. I measured the current draw to the motor when I lift the wheels off the ground, and it’s at about 0.5A. I then put it down and measured the current (note, the wheels aren’t moving now), and it’s around 1.1A. What’s going on? Any tips on what else I can try to get it to move!!

Cheers

EDIT: including picture so you get an idea of the size of the RC car

Here's OP's pic.

YW :wink:

Bilz:
8 AA batteries in parallel reading at about 10 V

That would be series, then.

The problem isn't the motors, especially if they came with the RC car. The L293D chip is only able of outputting 600mA per channel, and you're reaching 1.1A, which is way more than that. Use the L298N motor driver instead, which can draw up to 2A per channel.

androidfanboy: Use the L298N motor driver instead, which can draw up to 2A per channel.

No, don't do that either. If you're going to buy a new driver, you might as well buy a modern one that won't drop 2V at least, almost 5V drop at higher current.

Pololu has loads to choose from to suit various voltage and current requirements, all modern technology, and don't need a heat sink the size of a truck.

What was the original power supply voltage? Might have a worn out gearbox, sounds like a lot of power (5 Watts) just to spin unloaded wheels.

kenwood120s: No, don't do that either. If you're going to buy a new driver, you might as well buy a modern one that won't drop 2V at least, almost 5V drop at higher current.

Pololu has loads to choose from to suit various voltage and current requirements, all modern technology, and don't need a heat sink the size of a truck.

True, you could use the Pololu motor drivers, which are very good. I personally use them a lot and they're extremely compact. One of my favorites is the DRV8835 dual motor driver which can handle up to 1.2A continuously per channel. I see the L298N's around on the internet a lot but haven't tested them myself. Thought they would be an easy-to-get Amazon part. Thanks for informing me that they have an output voltage problem.

androidfanboy: I see the L298N's around on the internet a lot but haven't tested them myself. Thought they would be an easy-to-get Amazon part. Thanks for informing me that they have an output voltage problem.

They are easy to get, but ancient technology, which is why they're so inefficient. That inefficiency goes to heat, hence huge heatsink.

kenwood120s:
Here's OP's pic.

YW :wink:

That would be series, then.

Yep, thanks :slight_smile:

Okay, I guess I'll try one of the pololul drivers.

The 600 mA peak explains the ~1.1A across the motors (using 2 output pins in parallel). I don't actually know the current requirements of my dc motors, but if I connected all 4 output pins in parallel i should be able to get ~ 2A, right? I just want to know what my current requirements are!

Bilz: The 600 mA peak explains the ~1.1A across the motors (using 2 output pins in parallel). I don't actually know the current requirements of my dc motors, but if I connected all 4 output pins in parallel i should be able to get ~ 2A, right? I just want to know what my current requirements are!

Well, it depends. 2 motors in parallel is twice the load as 4 motors in parallel, assuming they are adequately powered. That being said, if the RC car is light or if you're measuring free-spinning current then that's an OK approximation to just double it.