DIY Electronics
This section was the most difficult part of the construction. My system was designed to use stepper motors. For a person like myself with a very basic knowledge of electronics a stepper based system was good starting point. I must admit I ended up having problems with consistent performance with steppers. I never did find all the answers to these problems during the construction of the stepper system. One detail that came to light was using a stepper that was too small for the application. Case in point was the Z axis of the machine. Gravity affects the Z axis the most of all three axes. Using a 300 oz in motor just could not push the axis reliable up and down. Add to my delusions of running the Z at 100 ipm and the situation became worse.
I did resolve the problem when I switched
to a large servo with a gear reduction. I believe the lack of reliable performance were related to my lack of
knowledge regarding the use of shielded wires, proper grounding techniques and motor sizing. The term that comes up frequently in the DIY CNC user groups are issues
of EMI or
Electromagnetic interference. This interference can cause a stepper to lose
position and aversely affect the correct dimensions of a part. This applies to a
servo also. Another concern is also where you rout the various wires from the
control panel to the motors on your machine. . It is
recommended to keep the encoder wires away from the motor power lines. In my
case I routed the encoder wires on the outside of the cable carrier. This
helped minimize interference from the higher voltage and currents of the
servo power supply lines.
Steppers or Servos
I would never be bold enough to make a recommendation as to which motor
type is the correct choice. I`ll just mention some of the pros and cons of
the two motor types..The cost of a stepper system is less then a servo.
Steppers can be direct drive. Servos require a timing belt and pulley
reduction to achieve their maximum performance. This adds additional costs
to a servo system. Most electronic devices cause EMI problems. As a result,
servo systems can be even more prone to adverse affects of
interference. When I switched to servos. I did end up purchasing
differential servo wiring which were premade by
US Digital to
minimize EMI problems. This added nearly $200.00 to the price of the servo
system just for the encoder wires and small circuit boards that were
retrofitted to the encoder heads.
