Arduino Uno + Tamiya 70168 Twin Motor Gearbox

So i am curious to see if I would be able to run two Tamiya 70168 Double Gearbox off a Arduino L293D Motor shield. I've been able to run one Tamiya Double gear box, but im not sure if the Arduino Uno would be able to handle two of them. The motor shield is capable of running 600mA of constant current and a peak of 1.2 A per motor channel. The motors in the gear box are FA-130RA type. They run on 1.5-3.0 volts and have a stall current of 2.2 A. The arduino uno runs on 5V.
Do you think I would be able to accomplish this? running two twin motor gearboxes with each motor hooked up to each motor shield channel? If not, why not?
Want to use this for my engineering project, where we have to build a sumo robot under 2.0kg.
Would really appropriate it if you could give me some advice! Thanks!
Motor Specs: https://www.pololu.com/file/download/fa_130ra.pdf?file_id=0J11
Motor Shield Specs: Overview | Adafruit Motor Shield | Adafruit Learning System
Arduino Specs: http://www.arduino.cc/en/Main/arduinoBoardUno

Do not power motors from the arduino. Motors need a separate power supply.

Yes zoomkat, I do not plan to power the motors with the Arduino. The motors would be powered by the L293D Motor shield. It directly plugs in ontop of the Arduino. The Arduino has a power source of 6 x AA's.

So would it be possible to run 4 x FA-130RA type motors off the L293D Motor Shield, if each motor is connected to each motor channel?

According to adafruit:

4 H-Bridges: L293D chipset provides 0.6A per bridge (1.2A peak) with thermal shutdown protection, 4.5V to 25V

So you have four bridge - one for each motor - so far so good. But each bridge can only handle 0.6A - while each of your motors need a minimum of 2.2 amps (because when a motor is at a dead stop - that is the same as a stall condition!).

I doubt that the bridges would be very happy being asked to supply 4 times the current needed that they can supply, when tell the robot to start moving...

Furthermore, you are very unlikely to get that amount of current out of the L293D - because to do so, you need external heatsinks, and maybe even some active cooling. Back when the L293D was young, you could easily get DIP IC heatsinks for it that would clip on, and hug the middle ground pins that also act as heatsinks for a PCB pad (which I think the shield has - but it isn't sufficient for the IC, honestly). The heatsink had a couple of fins, and would conduct both the heat from the IC and the pins to the ambient air.

Lastly, you say your motors can handle a max of 3.0 volts, while the L293D (and by extension the shield) supplies a minimum of 4.5 volts to motors. You would be running the motors at a minimum of 50% over their limits. Your battery voltage should be sufficient if using alkalines (aka - 9 volts), but if using rechargeables (7.2 volts) it may be iffy. Note that the bridge will drop about 1.4 volts or so on the output, due to it being a bipolar design (0.7 volts per transistor).

Hello --

Sounds like you are running with an Adafruit Motorshield V1 or one of numerous clones, with 2-L293's and a shift register. Try googling something like "stacking L293's arduino" &c. There have been folks posting on forums in re this strategy of upping the current available to motors.

Also, I know of only one source, Pololu, for compatible motors you might be interested in:
6V, 800mA stall

L293 chips are available from numerous vendors. If you go this route, be sure to line chips up notch over notch.

Best of fortune in your project.

Mark

Thanks cr0sh and bambuino for your input! Would using another type of motor shield be a better option? I’ve looked into stacking the L293D’s and have seem mixed reviews of doing this. Mostly because by stacking the L293D’s on top of each other doesn’t allow for the heat to be dissipated away. So I think by best option would be to look for a more suitable motor shield.

Any recommendations on a better motor shield that would be able to handle 4 x FA-130RA type motors?
Or should I look for better motor chips than the L293D?
Or use different motors with the gearbox? I found ones that are 6V and 800 mA stall.
Here is the motor link: Pololu - Brushed DC Motor: 130-Size, 6V, 11.5kRPM, 800mA Stall

I think Pololu has some high current motor drivers fitting an Uno R3 form factor, dual channel though.

I re-read your original post. 2.2kg is quite a beast. And four drive motors, where my familiarity with sumo design is for 2-wheel drive. Have you considered a 2-wheel design with tires that can offer better contact patches than stock Tamiya tires? Is the second gear box added for weight increase to fulfill the 2.2kg's (kinda an insignificant gain)?

For stacking the L293's, seems the top chip's pins can be formed and soldered on with some airspace. I don't have the chips in front of me, a bit of a guess there. Small wire leads to extend the height?

Adafruit is producing an R3 shield with better current handling abilites. Try look it up.

Trust that I probably know less about this than yourself, just curious what I might be able to learn from your travails.

Patboza:
Thanks cr0sh and bambuino for your input! Would using another type of motor shield be a better option? I've looked into stacking the L293D's and have seem mixed reviews of doing this. Mostly because by stacking the L293D's on top of each other doesn't allow for the heat to be dissipated away. So I think by best option would be to look for a more suitable motor shield.

That - and nothing like that is noted on the datasheet - in other words, results may vary for you. As a device with bipolar outputs, you really shouldn't parallel the bridges because the transistors won't share a heatsink (unlike the parallel mode in the L298, where you can double the output because the transistors are on the same die) - and thermal runaway can be an issue (basically letting the magic smoke out). If stacking the L293 was a valid thing to do, it would be mentioned by the manufacturer.

Patboza:
Any recommendations on a better motor shield that would be able to handle 4 x FA-130RA type motors?
Or should I look for better motor chips than the L293D?

If you are serious about this, I would look into MOSFET-based controllers; another option (but with the same voltage drop limits of the L293) would be an L298 based bridge (one per motor, with each bridge placed in parallel mode and a good heatsink attached - see the datasheets for details).

Patboza:
Or use different motors with the gearbox? I found ones that are 6V and 800 mA stall.
Here is the motor link: https://www.pololu.com/product/1117

800 mA is still too large for the L293 - but for the L298 (which can drive two DC motors - each at about 1.8 A or so, with a good heatsink) it would work. Just mind the voltage drop and min voltage issues.

Hi Patboza,

I tried and failed to run a single Tamiya 70168 on a L293D, but that was a raw L293D, not a shield or module. I may be wrong, but I seemed to run afoul of the L293D's thermal shutdown. In any case, it was a dead end and I wouldn't recommend that L293D for even a single Tamiya 70168 with stock motors. Two 70168s? Best of luck.

I ended up buying a L298-based module off of EBay for cheap (due to free shipping). That worked well. I have since used the same L298 module to power a 4WD skid-steer chassis, with each wheel driven by its own motor. The module powers all four motors just fine. Having said that, if I find a decent MOSFET-based controller for a reasonable price to my door, I'll jump at it.

Heed all of cr0sh's recommendations. All are sound.