Hi,
I'm making a small drone with 8*16mm coreless 3.7v motors. It controls by a node mcu (A development bored with wifi). When controling the speed of motors nodemcu's output signal ranges from 0v to 3.3v then the supply to a motor should be range from 0v to 3.7v at 2A (may be less but I want to be secure) current (for a one motor).
I used one d313 transistor (only transistor) with my 3.7v battery then at highest speed it gives output of 2.5v or less.
Can anyone help?

 

With only the information provided, no, I can not help with this. There must be some other requirements for such an application. And does it really have 8 motors? You would need to use pulse width control to avoid having very poor efficiency. And a 2SD313 is a slower speed transistor so it would not be a good choice for a switch-mode power controller. Really you will need to use FET transistors for the control system. And how many motors will be controlled by each output?

 

With only the information provided, no, I can not help with this. There must be some other requirements for such an application. And does it really have 8 motors? You would need to use pulse width control to avoid having very poor efficiency. And a 2SD313 is a slower speed transistor so it would not be a good choice for a switch-mode power controller. Really you will need to use FET transistors for the control system. And how many motors will be controlled by each output?

Thanks for your reply
It has 4 motors. One motor controled by one output. There are 4 outputs from node mcu. Yes I use PWM for control the speed of motors. I currently using Samsung 18650 3.7v battery but I will buy a li-po 3.7v because 18650 is more in weight. Motors are also 3.7v. Because of that at the highest rate of PWM (3.3v from nodemcu output) I need all 3.7v voltage for motor without voltage drop. Can you suggest me a circuit or something like that. I haven't a lot knowledge in electronics

 

Instead of bipolar transistors, you need to use FET transistors because they don't require very much gate drive, so they are simpler to interface. But to switch them on properly you will need a bit more voltage. But without adequate knowledge of electronics why are you starting a project like this???

 

What is PWM freq you are going to use ?

Motors rotating in only one direction ?

Regards, Dana.

 

You talk about Pulse Width Modulation but then present a maximum voltage, which sounds like an analog signal. So is the control signal an analog voltage, varying between some lower level and +3.3 volts? Or is it an off-on signal varying between zero and 100% on time? If the output is an analog signal then you will need a voltage to pulse width circuit, which is not a trivial thing to create. So please let us know which it is.

 

Small drones that you can buy use little 3.7V motors with brushes that soon wear out because the motors were designed for occasionally opening and closing a CD drawer, not to run continuously for six minutes per drone flight. Cheap little beginners RC model airplanes use these motors. I replaced the motors in mine up to 6 times in each airplane.
My larger RC airplanes today use 7.4V brushless motors that last forever. Good drones also use a higher battery voltage and brushless motors.

 

Instead of bipolar transistors, you need to use FET transistors because they don't require very much gate drive, so they are simpler to interface. But to switch them on properly you will need a bit more voltage. But without adequate knowledge of electronics why are you starting a project like this???

This is a project with microcontroller. The only thing I want to know is how to control the main voltage according to the pwm of microcontroller without a voltage drop thats why I asked for help

 

You talk about Pulse Width Modulation but then present a maximum voltage, which sounds like an analog signal. So is the control signal an analog voltage, varying between some lower level and +3.3 volts? Or is it an off-on signal varying between zero and 100% on time? If the output is an analog signal then you will need a voltage to pulse width circuit, which is not a trivial thing to create. So please let us know which it is.

It is a pwm signal. Not a analog signal

 

Small drones that you can buy use little 3.7V motors with brushes that soon wear out because the motors were designed for occasionally opening and closing a CD drawer, not to run continuously for six minutes per drone flight. Cheap little beginners RC model airplanes use these motors. I replaced the motors in mine up to 6 times in each airplane.
My larger RC airplanes today use 7.4V brushless motors that last forever. Good drones also use a higher battery voltage and brushless motors.

Thanks for advice

 

It is a pwm signal. Not a analog signal

The challenge that I see is that to fully switch on an FET, you need a higher voltage. But the first step would be to try the circuit using an FET device that can handle the motor current. You will also need to add a diode across the FET to allow the motor current to keep flowing when the FET switches off. That will protect the FET from the inductive spike as it switches off, plus improve the efficiency a small amount. Sorry I can't suggest a specific device, but there are other folks reading this who certainly can help with that.

 

There are many electronic toys and items that use tiny surface mount Mosfets that conduct a few Amps when the gate-source voltage is only a couple of volts. I also do not know their part numbers but a search on Digikey will find them.

 

Hello,

As for the mosfet, have a look at the sq2310.
It has a V(gs)th of 1 volt max.

Bertus

 

The threshold voltage is when a Mosfet is almost turned off. Most people want to know the Vgs when it is turned on.
The SQ2310ES Mosfet turns on with a max D-S resistance of 0.042 ohms when its Vgs is 1.5V.
I tried to make a photo of one but it is too small to see.

 

OK, if the FET transistors can be fully switched on with that output voltage then it should work. From the description it is not clear if this is a new project or the repairs to an existing project. AND, note that the transistors will need to be in the negative motor lead, , since the source will be the common for the gate signal of all 4 motors.