Hello,
I have built this motor circuit for my Arduino and when running it only gets less 1v and the motor spins very slowly and my bigger motor doesn't spin at all. I have attached the diagram that I followed below. The Motor should be getting 5v from the Arduino although something seems to be limiting it.

Parts:
270 Ohm 0.5 Watt Metal Film Resistor
1N4001 Rectifier Diode
2N2222A NPN Transistor

 

The transistor may be too small for the motor load.
And the 5V from the Arduino may not be able to supply the required currrent either.
It is best to run the motor from the power supply, not the Arduino. And use a logic level power FET to do the switching
What current rating does your motor have?

For example...
https://www.instructables.com/id/ArduinoMicrocontroller-MOSFET/

 

The transitor switch is typically used to control a higher voltage to drive the motor. Please post your sketch along with the diagram so we can tell exactly what you are doing in order to knowledgeably comment on it.

 

What does pin-3 in the Arduino look like?
Maybe it is only high 1/5 of the time.

 

Arduino typically cannot power a motor, only provide the control for it.

 

That circuit looks fine. Unless the motor is drawing way more than the 5V supply can give, it should work, assuming the pin driving the base is set to high.

Bob

 

The Voltage is being pulled down because the Arduino cannot supply the current to power the motor.

 

You did not say so I am sorry that I must ask. Is it a 5V motor? What is its no-load running current and its stalled current ratings?

The loaded output of the Arduino is probably 4V and the transistor base is 0.7V so the 270 ohm resistor provides a base current of (4V - 0.7V)/270 ohms= 12.2mA. The transistor can saturate with a collector current of 12.2mA x 10= 122mA.
If the motor resistance is less than 4.8V/122mA= 39.3 ohms then the motor will not start running.

Measure the resistance of the motor while slowly turning it and post the lowest resistance it has when it is not on the circuit.

 

How are you powering your Arduino board? If the board is being powered by a USB 2.0 port on a PC you likely will not get enough current from the 5V out pin of your Arduino board. You really want to get an external DC power source like a simple wall wart with the standard 2.1mm x 5.5mm DC connector having center pin positive. Like this one. The Arduino powers well from between 7 and 12 VDC external power. Also, the Arduino 5V pin is not an infinite source of power, it has limitations. You need to know the load current or in this case the motor current. The circuit looks fine so my money is on the inability of the motor to get its rated current and that assumes this is a general purpose 3 to 6 VDC hobby motor.

Ron