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I am creating a six-wheeled robot which I am controlling using a PS2 remote and an Arduino. I am using a L298N Motor/Stepper Driver as the method for controlling the six motors.

The motors are designed to run off a voltage of 7.2 V each. I am using 6 × 1.5 V AA batteries in series in a battery pack for powering the motors. I am using 6 × 1.2 V AA batteries in series in a battery pack for powering the Arduino.

The structure for how the wires connect up to the motors that came with the robot chassis, the motor driver and the Arduino is as follows:

schematic

simulate this circuit – Schematic created using CircuitLab

(This is my first ever schematic and took me 2 hours to do so I tried by best with it).

The two blue X points show where the robot chassis came with one wire splitting into three separate wires.

  • When I place the voltmeter across the 12 V+ point and the GND points on the motor driver I get 0 V but when I place the voltmeter across the 12 V+ point and another GND pin on the Arduino I get the full 9 V.
  • When I place my voltmeter across either of the 2 X points I get a voltage of around 3 V which is not enough to power each of the three motors on each side of the motor driver. The motors still move at quite a fast rate but when placed onto any type of floor, the wheels don't seem to move at all and the power given off by the motors is not enough to make the robot move.

I tried fixing this by increasing the power supply given to the motor driver by increasing it from 9 V to 15 V.

  • When I place the voltmeter across the 12 V+ point and the GND points on the motor driver I get 0 V but when I place the voltmeter across the 12 V+ point and another GND pin on the Arduino I get the full 15 V.
  • When I placed the voltmeter across the 2 X points I got around 10 V which was more than the three motors on each of the two sides needed. The motors went extremely fast when this happened. But when I placed it back onto the floor afterwards with 10 V the robot still did not move.

I have double checked my code and it does do the correct thing.

Here are links to items that I used:

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    \$\begingroup\$ That's the exact chassis you are using, correct? So it already has gearing for the motors? If so, then the problem is your batteries and your driver. Six AA batteries can barely power a flash light, let alone a 6lbs robot. \$\endgroup\$
    – DKNguyen
    Dec 27, 2021 at 17:20
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    \$\begingroup\$ Read the datasheets before buying. The chassis one says "We recommend a 20A motor controller" (actually, one for each side). The motor controller says "Max 2A". (and if it COULD supply 20A, the batteries can't.) \$\endgroup\$
    – user16324
    Dec 27, 2021 at 17:24
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    \$\begingroup\$ You need much more current than the AAs can deliver, NiMH, Lithium or lead cells would be more suitable. \$\endgroup\$
    – Neil_UK
    Dec 27, 2021 at 18:07
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    \$\begingroup\$ @Neil_UK By lithium cells do you mean the thin circle ones? \$\endgroup\$
    – DigitalRookie4
    Dec 27, 2021 at 18:28
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    \$\begingroup\$ @DigitalRookie4 Sorry, I forgot you put Rookie in your name. I meant lithium cells that can supply adequate current, like 18650s or RC packs. Lithium coin cells (thin circle ones) have an even lower current output than AAs. \$\endgroup\$
    – Neil_UK
    Dec 27, 2021 at 19:27

1 Answer 1

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The comments have basically answered your question, but allow me to summarize.

  1. The L298N is an inadequate motor driver for this robot. It has a high voltage drop, and it's rated for only a few amps. Each motor on the robot can draw up to 6.6A at 7.2V, so ideally you should use a 20A motor driver for each side of the robot. Here's an example: RB-Dim-47

  2. Your batteries have way too little current capacity for these motors. They need 12-40A. Your AA battery back can supply maybe 1. Get yourself a 2S lipo pack with a capacity of 6000mAh and a discharge rating of at least 10C. These are cheap, high performance, and readily available. Stick to respected brands if you can since you can trust that the ratings are accurate.

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  • \$\begingroup\$ Two questions, 1. Could I get away with using a 10A motor driver for example, this one: robotshop.com/en/… 2. Is 6A at 7.2V just touching it deadly because I have seen on some post that current above 2A can be dangerous. \$\endgroup\$
    – DigitalRookie4
    Dec 29, 2021 at 12:07
  • \$\begingroup\$ One more I forgot to mention but I could not edit into the first comment, 3. I am searching for potential batteries and most of them are 7.4V rather than 7.2V and I can only find 80C and not 10C, will this burn out the motors? \$\endgroup\$
    – DigitalRookie4
    Dec 29, 2021 at 12:25
  • \$\begingroup\$ The way electric shocks work is like this: your body is a resistor, and depending on the voltage you touch, a certain amount of current will flow through you according to ohms law. You have a relatively high resistance, so as a rule of thumb, voltages lower than 50V aren't dangerous. The current rating on a battery is the limit, but it will only flow what ohms law allows. If your skin is wet your resistance becomes lower, but even if you're sopping wet 7.2v isn't going to hurt you. it doesn't matter if the battery is rated for 10 thousand amps. \$\endgroup\$
    – Drew
    Dec 30, 2021 at 1:31
  • \$\begingroup\$ The C rating is essentially the current capacity of the batteries. A 6Ah battery with a C rating of 10 can supply 60A (capacity x C rating). Just like with your electric shock question, the batteries will only flow what the motor impedance allows, so a higher C rating will not hurt anything. \$\endgroup\$
    – Drew
    Dec 30, 2021 at 1:33
  • \$\begingroup\$ You should not use a motor driver with a lower rating than the current the motors may draw. It can be done if the driver is good quality and has overload protection. If you use a lower rating driver without sufficient protection, it may simply overheat and burn out once you exceed it's ratings. \$\endgroup\$
    – Drew
    Dec 30, 2021 at 1:37

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