First off I guess let me introduce myself. My name is Stacy and I'm building 3d printers which has brought me to this sight. I am successfully using stepper motors right now and following a few builds of others using closed looped brushed DC motors and in the process of implementing it into my design. Next step passed that is to move to closed loop motor control with a BLDC. Using FOC or instaspin. I've probably watched all of the videos on youtube a couple of times and (think, but not sure) that FOC is just Field oriented control and instaspin is the software but its still kind of unclear to me.
Ive been looking at the DRV8305 that has three half bridges to control a BLDC(brushless) motor and each half bridge has a current sensor that senses the back EMF(electro magnetic field) and uses this data as an encoder for closed loop motor control. There are actually quite of few DRV chips that control DC motors and I (think) that this might be the one I need. What I would like is and maybe someone me be able to point me in the right direction is one that is for closed loop motor control without an encoder, using the three shunts for back emf. This chip controlling a N channel FETs that can supply Quite a bit of amperage preferably as high as can be had. Most RC BLDC motors can operate at very high rpm and from what I'm reading these bldc chips can only operate at or below around 8,000 rpm. Have I read this wrong? So I'll ball park what I need
6 BLDC driver chips on one board
6 Encoder counters(just in case)
36 N channel Fets, would like to hang Fets off the side of the board to be screw to a cooling plate
4 more FETS for heaters (not sure what to choose here)
Processor Some sort of ARM processors
USB
Eithernet network connectivity
Blue Tooth
SD card
12 limit switch inputs
3 thermistor/ thermal coupler probe inputs
reset button
Estop input on an interrupt pin
5 relay output pins
Ive added other axis for CNC machines for the future. What am I missing. Thanks in advance for the help.
Goals
- Is to get closed loop motor control working with the 3d printer with a DC motor. The DC motors are big bulky and they wear out.
- Get the closed loop system working on the 3d Printer.
- A single axis closed loop motor controller working in the printer with a BLDC(brushless) motor.
- All three axis plus extruder.
Advantages
- Of the BLDC is power to weight ration, instead of a stepper motor the size of an egg it can be the size of a thimble.
- Wiring- 3 wires as opposed to four of a steppe, and these three wires will allow closed loop motor control. Open loop with a stepper is minimum 4 wires and closed loop adds a minium of 4 wires plus the pain of mount and cost of an encoder.
- A lighter smaller BLDC motor would decrease the weight of the axis substantially. Seeing as the stepper is the majority of the weight. In a CNC machine Axis weight is not as crucial as a 3d printer because 3d printers are shifting directions during infill operations at extremely high rates. Cutting down weight on these axis so that they can be going one direction and instantly be going the opposite direction while not shaking or vibrating the entire machine is crucial for a (fast) stable print environment. With heavier axis loads belts tend to act like a guitar string and vibrate and these vibrations show up in the print.