Bye Bye Belts!
RepRap Lorenz does not use timing belts. Instead it is driven by wire wound helically on a pulley on each stepper motor.
The error caused by the change in wire angle as the helix winds 300mm of wire is about 40 microns.
The nice thing is the pulley is so easy to make. It’s just a 10mm diameter bar drilled through with a 5mm hole and with a grub screw drilled and tapped into one end. Half way along there’s a 1mm hole. A loop of the wire goes through that, runs between the flat on the motor shaft and the inside of the pulley, and is trapped under the grub screw which also clamps the pulley to the shaft. The wire can’t slip, and neither can the pulley. Even in small quantities the pulley should be as cheap as timing-belt toothed pulleys, and – of course – the wire is a lot cheaper than timing belt.
Here is the video of the first test movement of Lorenz. Using a Duet 0.6 with David Crocker‘s firmware Lorenz was asked to home all the axis, move in 10mm steps in X, Y and Z axes and then complete a dry run of printing a file. All of these it did successfully. We were on standby to hit the reset button in case the motors were plugged in backwards…
Here is the wire tensioner at the other end of the axis to the motor. The wire runs over a V ball bearing, which is lifted slightly by a grub screw in the hexagonal printed part. Again, V bearings are very low cost because the textile industry uses millions of them.
Note the use of tubes rather than solid rods for the slider to slide on. The wiring and the Bowden tube for the filament will run up those, which will – we hope – be very neat.
You can also see from the video that there are no wires running from the bottom to the top of the machine (the mess of wires at the bottom is purely experimental…). This absence of wires is because the rods form the connection to the stop-switch at the top of each column. Details of how the wires run will be in the next blog post.
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