# Running bldc motor without hall effect sensor or back emf [closed]

I'm new to working with motors. Recently I was working on 3 phase BLDC motor. I needed to build a gate driver + 6 MOSFET circuitry but instead, I have BDC motor drivers from Hindustan Dynamics called Hercules Driver. Now, I need three BDC drivers to drive one 3Phase BLDC motor. I did all the connections and using Arduino mega 2560 I got everything working but without using feedback from either hall sensor or back EMF. I'm applying following sequence to the motor phases

 A      B      C
1     -1      0
1      0     -1
0      1     -1
-1      1      0
-1      0      1
0     -1      1


where 1 is VCC and -1 is GND and 0 is OFF(open circuit). Surprisingly motor starts spinning without any problem. Then I moved rotor manually to a random position and again tested with code even then motor starts spinning in right direction and at the right speed. I tried moving motor rotor to a random position different from where it stopped and each time motor rotates perfectly. As I understand from the literature that it takes some kind of feedback to drive BLDC motor but I don't observe that here. My motor has the following configuration:

Number of poles: 16
Number of winding slots: 18
Motor voltage: 24V
Current cap: 3 Amp


What is the role of feedback and how to use it? Thanks in advance.

## closed as unclear what you're asking by ThreePhaseEel, Marcus Müller, Voltage Spike, Daniel Grillo, jonkNov 30 '16 at 23:43

Please clarify your specific problem or add additional details to highlight exactly what you need. As it's currently written, it’s hard to tell exactly what you're asking. See the How to Ask page for help clarifying this question. If this question can be reworded to fit the rules in the help center, please edit the question.

• What is your actual question? – PlasmaHH Nov 30 '16 at 12:46
• Assuming the actual question is: "what does feedback give you?" - 3 things : (1) your current scheme will probably fail at higher speeds, and stall with any kind of load on the motor (2) it won't track instantaneous speed changes at all and you may have to ramp speeds up and down gradually (3) it'll be hopelessly inefficient, like a simple stepper motor drive, because you can't tune the drive voltage (PWM duty cycle) to match the motor's actual requirements. – Brian Drummond Nov 30 '16 at 14:21
• @PlasmaHH I have updated my post, I want to know what is the role of feedback if a motor can rotate on its own and how to use it(feedback measurements)? – Vinay Joshi Nov 30 '16 at 14:42
• @BrianDrummond Thanks for your answer. So using feedback one can maintain synchronization between electrical and mechanical rotations and helps in avoiding problems listed in your comment, right? – Vinay Joshi Nov 30 '16 at 14:51
• BLDC motor control is a topic on which books can be written, the questions needs to be more specific. That being said you can drive bldc motors open loop, but they won't be able to react to torque loads like a motor in feedback will. There are many ways to get feedback from the motor. Back EMF is one of them. – Voltage Spike Nov 30 '16 at 17:02