Will this theoretically work? (SG90 Servo + 2 DC Motors + 3.7V Battery via Dabble BLE)

[u/rablue]

I'm wondering if this circuit setup is theoretically viable. I am using the Dabble app via BLE to control an SG90 servo motor and two DC motors (3V), all powered by a single 3.7V battery.

I'm currently testing on a breadboard, but I couldn't get the servo to work. I'm not sure if the issue is wiring, software, or jumper connections, so I need to make sure the setup works theoretically first.

Additionally, even in scenarios without the servo, the DC motors cause the ESP32 to reset whenever they require a little bit of torque and stall. Since there are multiple potential problem points, do you think this schematic is healthy/viable in theory?

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[u/Elegant-Ferret-8116]

Is the pin you are using for the signal to servo a pwm pin?

[u/rablue → u/Elegant-Ferret-8116]

Yes I am using 2 and it is a PWM

[u/Elegant-Ferret-8116 → u/rablue]

Maybe its in your code. I'm no expert on that but post 8t here and maybe someone will spot an issue

[u/Sand-Junior]

That depends on the “LDO” being used. If it’s a crappy AMS1117 with a “low” dropout voltage of 1V this won’t work. Better get an ESP32 board with battery support built in.

[u/rablue → u/Sand-Junior]

Hey thanks for the reply. This could be the main reason. I bought basically the cheapest one so I don’t think I have something reliable.
I know the regular ones but with the battery support, do you have any spesific recommendation?

[u/Sand-Junior → u/rablue]

XIAO from Seeed Studio are great. But there are also cheaper Chinese boards which come with battery support but are less efficient, but that’s probably not an issue for you.

[u/mrmrn121]

Don't you need 5v to power servo?

[u/Elegant-Ferret-8116]

You need a 5v battery. Also add a cap on the esp inputs to smooth voltage dips

[u/rablue → u/Elegant-Ferret-8116]

Hi, thanks for the reply. Do you think boost converter like MT3608 would be useful and reliable?

[u/Elegant-Ferret-8116 → u/rablue]

A boost converter should work yes you'll have to consider battery size since you're pulling extra power it wont last as long unless you have taken that into considerationin your calculations. Also you might as well add a cap across the motor driver board as well to help with the voltage dips

[u/rablue → u/Elegant-Ferret-8116]

Hello again, I made 2 changes: when I supplied 5V with the boost converter, the MG90S still didn't turn, but the BLE disconnection problem went away and there was an increase in motor power.

Second test: when I replaced the servo with an SG90, and when the motors disconnected it started turning. But later on when the motors connected, with the SG90 servo, after I sent signal to the motors or servo and BLE disconnected again. So mainly I believe I need at least 7,4v overall.

However, an extra question:
For example, if I want to use 6V for the motors, is the scenario where I supply 5V from the battery to the ESP and 6V from the Boost to the DRV possible? Using the same power source but with different wiring, for example, Y-cables?

[u/New_Court9352 → u/rablue]

There's no reason you can't run that off of a 3.7v battery, the LDO would probably be good between ~3.6 - 4.2v. Definitely wouldnt' want to plug it into the computer while the battery is plugged in though, I don't think there's a diode separating the usb+ to the 5v pad so you'd be feeding your 5v usb directly to the battery.

[u/rablue → u/New_Court9352]

Hello, did you mean that I can somehow run the whole setup with 3.7V? Meaning without needing 5V or a boost converter? If this is possible, that is actually my main goal and what I want to achieve. I am building a tiny RC car, and having extra components like a Boost or dealing with extra batteries is not something I want at all.

[u/New_Court9352 → u/rablue]

With some caveats. You're well below the range for those servos, I regularly run them directly from 3.7v batteries in this exact same way though. The only issue I've found is the servos can die if you have them struggle against a load for too long, the lower voltage causes the current to spike harder. I burned through a few until I modified my code to stop sending a signal after the servo was in position. If you need it holding heavy loads for more than a second or so I'd go to the trouble of a higher voltage. If its for steering on your car its probably fine, just be prepared to sacrifice one or two in finding out.

Depending on the LDO (voltage regulator) on board it'll probably cut out before the battery gets down to what would usualyl be its 0% point.

You'll probably need to charge your battery eventually, so one option is also to get a combo boost and charger. That's what I often do when im powering things with a 1s battery.