Grounding power source used for both arduino and circuit branch

Forgive me if this is a stupid question. First time doing a build like this.

I'm building an RC car for a project in class. I can only use one 12V battery as a power source for both the arduino and the motor circuit (same as below only using two motors and an R3 UNO). The battery will power both the arduino, some components through the arduino, and this circuit. Is it still okay to connect the negative to the ground pin as shown?

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Generally speaking, you must always connect the ground of two circuits you have working together. In this case, when you connect the battery to the Arduino through the barrel jack, you’ve already connected the grounds, so that additional connection is redundant.

What transistor.
Two motors and low base current (~4mA) is likely going to fry the transistor.
Unless you use a darlington (TIP120).
Leo…

I appreciate the help with part sourcing :D

It's two 12V motors powered from a 12V battery with a max draw each of 1.06A and a min of 0.09A run using PWM. I figured this was the easiest set up.

And since you've been so helpful with the NPN, do you think a 3A Schottky will work as a flyback diode?

I very much appreciate all the help!

3A schottky sounds ok. Lower the base resistor to 470ohm for 2Amp. The TIP120 could use a small heatsink with that current.

Two PWM pins and two TIP120/1k with two motors and two diodes might be better. Or replace the TIP120 for a logic level mosfet (more motor power, less heat in the transistor). Leo..

Two circuits is doable, I could also use a less powerful diode then, I'm just trying to shave weight wherever possible to cut the car's track time. Every little bit counts and every extra part weighs something.

Never worked with mosfets, just transistors until now. From a cursory reading it seems easy to swap one for the other and I'd be able to ditch the base resistor. Anything I can do to coax more power out of these 150 rpm motors we've been saddled with is a blessing.

You're seriously making this so much easier. If I had a will I'd add you to it :kissing:

Got a recommendation for a specific mosfet to use either with the original setup or your two circuit idea?

Any TO-220 logic level mosfet with low Rsd(on) will do. Wise to us a gate resistor and a bleed resitor, but they can be very small (size). First image here. Leo..

Okay so if I'm reading that right the source and bleed resistor run to GND. With that setup from the first image I can still run the motors in parallel in place of that single motor right?

Yes, most power mosfets are good for several Amps. But you might want to use two on two different PWM pins (5 and 6 or 9 and 10). Then you can control power to each motor individually. Leo..

If I were using them on separate power trains I would, but it's unnecessary to control them separately since they're both powering the same drive axle.

https://www.adafruit.com/product/355 ← I'll use this on the single circuit you suggested, with both motors tied together then

Thanks for all your help!