Hello everyone, how are you? 
I have a school project that consists in a quadcopter that I am building with those small syma 5xc motors. I don't intent for now to make it able to navigate like a drone. I just need it to be able to take off and to level autonomously to a determined height value that I will send remotely.
For this project I am using an arduino nano connected to a WIXEL wireless module, DAC0808, ULN2003A as the motor drives and ultrasonic sensors to measure the height. I am not using ESCs or any other dedicated module or shield.
I want to make every part as simple as possible because I am working alone in this project and I still have to develop the code for a PID control. It is not planned for it to fly outdoors or stand against the wind. I want it to stay fixed in pitch,yaw and roll. Just lift over 20cm from a flat surface will be fine.
My question is about the best and simplest strategy to build this quadcopter leveler given my incomes.
First I thought about ultrasonic sensors fixed near each motor and control them individually in terms of height. But still I would have to fix the yaw movement somehow.
Then I went simpler: Placing only one ultrasonic in the middle and using only one arduino output channel to send a same signal to the 4 motors. Is that possible to lift the quadcopter stably the way I need it?
Thank you very much!