John,
Does the motor reverse on this machine? Or is it just set up to spin the wheel in one direction only. I dont have any idea why I am asking, other then maybe a posibility in the difference of the surface finish. I am still marveling at the great job you did on this machine too. Your def. way up there in the craftsman range in my book. Beautifull, clean and well detailed, just plain beautifull work......again.
Bob
Thanks for the good words Bob!
In answer to your question, the spindle motor is a standard three phase AC motor. Thus it's reversable by swapping two leads. Or, I can do it in the VFD.
But, I wouldn't for two reasons:
1) Running the wheel backwards no longer allows the wheel adapter and spindle nut to be self tightening. A safety issue.
2) The other two motors (hydraulic pump and dust collector) would also run backwards if I reversed the VFD.
Getting a bit off subject: There is a theory that a VFD cannot drive more than one motor. This is
not always true depending on how the VFD is to be used. In my case, its doing nothing more than phase conversion: 220V 1 phase in, 220V 3 phase out.
In my VFD, I'm not using space vector pwm mode, slip compensation, PID, or any feature that would preclude its use for multiple motors I can drive all three big motors (and the small shaded pole lubricator motor) off of one VFD. Also, in the grinder, I have no big inertias to accelerate. So I have no worries about simultaneous startup of the three units. The 1.5 kW VFD I'm using starts all three motors at once with no issues - even if I throw the switch on the grinder instead of using the VFD acceleration profile to start....
According to the VFD readout. the spindle motor takes 0.1A no load, with up to 1.5A during heavy grinding. The hydraulic pump takes 1.5A continuously, and the dust collector takes 1.2A (drops a bit when a hose is installed). I'm not sure how this is being done since the currents are lower than I expected. But, there is a current transformer on the rectified line voltage used as a HV DC supply voltage inside the VFD used to generate the outputs. There is no output current sensing apparent in the circuit.
I had to reverse engineer the output stage in the VFD out of simple curiousity since I design motor controllers for a living.... By the way, our motors and gearboxes are on the Curiousity rover that just landed on Mars. We provided actuators and microelectronics (IC's and stuff) for virtually all required movements: wheels, steering, robotic arm, etc... I did not design the motor controllers in the rover itself but was on the independant design review team. JPL did the elelctronics design in house.
The Mars Reconaissance Orbiter satellite relaying pictures back to earth
does have motion controller that I worked on.
Getting back to the VFD, what I do know is single phase input current when the VFD reads 4A, is over 8A since it blew the fuses I used on the incoming line! Since the remaining 4A+ required to blow the fuses is going somewhere external (the VFD runs very cool), I suspect the motor current readout on the CFD isn't the whole picture.
John
