I was going to suggest this at the start of the thread, but I thought it would be considered too Heath Robinson..
On Thu, 18 Jun 2020 at 20:40, Chris Albertson <[email protected]> wrote: > I'm making good progress on my 3D printed CNC conversion. I found a way to > 3D print a spindle controller that should work for most small milling > machines and small lathes. The cost is "almost nothing". These > machines' spindles are controlled by turning a potentiometer so my new > system simply uses a cheap model airplane servo to turn the shaft of a > potentiometer. The computer is 100% isolated from any high voltage or > noise. > > These small mills will never be able to do things like rigid tapping so all > they need is a simple and approximate way to control the RPM. This speed > control can be run "open loop" if plus/minus 20% is good enough or used > with a spindle encoder in a closed PID loop as long as the PID is > tunned not to aggressively. > > > For anyone who does not know about these hobby servos: > > - They are not full rotation motors. They turn only through about 250 > degrees, This is a good match to the pot as pots also rotate about this > range. > - The angle of the servo shaft is controlled by a PWM signal. > - They are "dirt cheap" starting at about $5 amazon.com/4-Pack-MG996R > < > https://www.amazon.com/4-Pack-MG996R-Torque-Digital-Helicopter/dp/B07MFK266B/ref=sr_1_2?dchild=1&keywords=mg+servo&qid=1592502600&sr=8-2 > > > - They accept a 5-volt control signal, so they have a built-in computer > interface. > - They are fast (enough) and can move from full-low to full-high on 0.6 > seconds > - They really are actual "servos" and have an encoder, motor driver, and > gears all inside. > > > So when LinuxCNC outputs a low-value PWM spindle control, the servo moves > the pot to the low position. As the PWM signal value gets larger the pot > is moved closer to the high-speed position. > > In the picture below is a cartoonish render. The green frame is one-piece > 3D printed, The red pannel and tan coupler are also 3D printed. The motor > sells on Amazon, four units for $20 and the pot is about a buck each. Four > M4 button head screws everything together. > > Here is a link to the current version CAD files and a viewer. I'll be > updating the files after the first prototype is printed. > https://a360.co/2N95AiL > I may make a top cover to protect the pot and keep fingers off the high > voltage. > > > > [image: Red Neck Spindle Control v6.jpg] > > > > -- > > Chris Albertson > Redondo Beach, California > _______________________________________________ > Emc-users mailing list > [email protected] > https://lists.sourceforge.net/lists/listinfo/emc-users > _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
