Simplist up down z for mobile gauntry

[transfrank]

Hello,
I am in the process of researching how to make my own mobile gauntry cnc plotter. I am trying to figure out what is the simplest up/down Z axis solution. I found a lot of complex designs where the Z positioning has a large travel through a a lead screw, but I need something really simple. Could someone point me to something like a plotter?
Thanks,
Frank

[PaulRowntree]

Hi Frank
If the plotter is always writing on a single XY plane, then any mechanism to remove the pen tip from the plane should work, no? What about a simple $10 PWM servo (the type that RC modelers and robotics hobby folks use) that would swing the pen away from the writing plane? A solenoid may work, bu the travel is usually very short, and they would heat up when energized for long periods of time.
Cheers!
Paul Rowntree

[CarveOne]

Originally Posted by PaulRowntree Hi Frank If the plotter is always writing on a single XY plane, then any mechanism to remove the pen tip from the plane should work, no? What about a simple $10 PWM servo (the type that RC modelers and robotics hobby folks use) that would swing the pen away from the writing plane? A solenoid may work, bu the travel is usually very short, and they would heat up when energized for long periods of time. Cheers! Paul Rowntree

The solenoid should be energized only when the drawing pen is down. A light tension spring should be used to retract the pen when not drawing. The spring should also apply a small amount preload to the pen while drawing so that during small irregularities in the drawing surface the pen does not skip.

CarveOne

[transfrank]

Thanks for your responses.

Can a solenoid system be made out of a big mechanical relay dissasembled and used for the motion? Is there a simpler way to make a solenoid mechanism?

I will look into the servos too.

[CarveOne]

Originally Posted by transfrank Thanks for your responses. Can a solenoid system be made out of a big mechanical relay dissasembled and used for the motion? Is there a simpler way to make a solenoid mechanism? I will look into the servos too.

Most mechanical relays have a fixed metal core inside the coil and a metal plate is attracted to the core when voltage is applied to the coil. The contacts move with the metal plate. They would not be useful as a solenoid.

Tubular solenoids come in push or pull types. An R/C servo will work but you need a way to operate it. The simplest way I know of is to use an R/C servo tester that can be purchased. No transmitter or receiver is necessary that way.

The pen holder can have a ball point pen spring inside to provide the preload function. I made a spring loaded BIC pen holder in one of the threads in this forum sometime during 2009. It was just a K&S brass tube that was sized to fit a BIC ballpoint pen.

CarveOne

[PaulRowntree]

Parallax Inc. (www.parallax.com) sells several microcontrolers that can provide PWM outputs to drive small servos. I have used the Propeller Protoboard to drive them... software is free via the Object Exchange. Cost would be ~$55 for controller, power supply, servo.
Cheers!
pr