I started some testing on some subsections of the BLDC motor controller and ran into some problems and learned several things. I'm working with chatgpt to resolve each issue and have been updating my schematic to reflect alot of the changes I am making. One thing I learned is that for the high side switch, the voltage from gate to source has to be 10-12v higher than the drain voltage because the drain voltage becomes the same as the source voltage once the switch is on. The voltage from gate to source then either has to start out as motor input voltage + 12 while still fitting within the voltage from gate to source max allowed voltage as stated by the datasheet or it has to rise dynamically as the source voltage rises such that the voltage from gate to source is 12 more than the source voltage as the source voltage rises to become the drain voltage. Fortunately, I can have the former for this 2430 motor since I can use 6-8.4v to supply the motor and the voltage from gate to source max value is 20v. This means I can use voltage from gate to source of 20v and this, when mosfet is first switched on, does not fry mosfet but as the source rises to become 8.4v, 20v-8.4v is still 11.6v which is sufficiently high to enable the mosfet to still stay on without anything dynamic set up. If I want to go with a 12v motor supply on some of the bigger motors later on, I will need a bootstrap circuit to supply the highside mosfet with a dynamic voltage from gate to source that rises when source voltage rises. So I added that schematic diagram to this as well as an option. I also can use a mosfet driver for this but was hoping to cut that cost and added volume taken up by just using discrete components rather than a IC for this.



Anyways, to break things down even more in testing, I decided to just test turning on and off a single highside mosfet using a pair of lab power supplies, one to provide 20v and one to provide 8.4v. To turn on I connected the gate and source to my 20v lab power supply and I connected my red alligator clip of my 8.4v lab power supply to the drain and then measured from source to the black lead of the 8.4v power supply and verified 8v on that test which worked - proving the mosfet was in fact on. I then removed the black alligator clip of the 20v lab power supply from source and shorted the source to the gate to drain the internal capacitor inside the mosfet and then tested from source to the black 8.4v clip and sure enough it was near 0v so was off. But it did gradually climb back up to 8.4v after the short from gate to source was removed due to capacitive coupling and leakage according to chatgpt. So I will need to add a 10k ohm resistor between gate and source pins to short it automatically and keep it fully drained and off fully when it's supposed to be off.



So I plan to just gradually add components little by little and test after each thing is added to ensure it is working right still after each little change and this way gradually build out the circuit, proving each thing works as we go. This is because things have all these gotchas and "oh you didn't know this little detail?" that keeps coming up and proves it was more complicated than I thought. So I just have to prove every little thing as I go. To try to find out what is wrong after the whole thing is built would be WAY harder than to figure out what went wrong when a single component is added and it was working before said component was added. So that's how I will be able to overcome this challenge best I feel.



Note: Reminder: I am building a custom BLDC motor controller because an off the shelf one would not have enough miniaturization to fit into the tight space constraints I have to work with. Also, building my own gives my software more precise control of every little advancement of the rotating magnetic field and along with that I'll have the ability to PWM the advancements to make them more smooth, less noisy, and have torque control as well this way which means the fingers can be rough and fast in movement as needed or slow and gentle and dainty or slow but powerful etc. I can also create acceleration profiles that match human finger joint acceleration in order to have the movements look very natural just like a human's movements which is very important to me. Just alot of fine precision is possible when its all my own circuit I feel. While off the shelf ones may have some of this functionality, the price often reflects that and is then prohibitive. But in any case nothing is off the shelf with this level of control AND the ability to so finely tune its form factor and volume envelope to fit my exact needs in space on a per motor basis.