Re: *soon to be* ORD Bot owners, assemble!
Posted: Mon Jul 16, 2012 11:13 pm
I wanted to use the T slots in the aluminum extrusions for wire routing, partly because it'll make a nice tidy installation, and partly because I wanted to use it for electrical isolation, but when I started planning the wiring, it's difficult to separate the motor wiring from the sensor wiring. The wiring tends to group by axis or area, and the sensor wires are almost always bundled with motor wires. For example, the wires running to the extruder are typically stepper motor wiring, heater wiring and thermistor wiring. Maybe a fan. It's difficult to separate the therrmistor wiring from the other power wiring. My suggestions:
We should probably be using 10K thermistors rather than 100K thermistors. The additional power is negligible and the 10K thermistors will be more noise tolerant.
The controller should be intelligent enough to sample temperature data when there isn't any motion on that axis, or do long term averaging to eliminate the noise from the very slow moving temperature data.
Twist the wires in pairs. Twisting the thermistor wires can do wonders for noise rejection. Twisting the motor wires in phase pairs should help a lot too. The twisted pairs take up a lot more space in wireway, so that may not be possible, but if you can do it, it's well worth the effort. I'm running a lot of wires through small cable track. Maybe I should have bought the next larger cable track for the big bundle of wires from the extruder and X axis. Even better, if I have noise problems, I might run two parallel cable tracks with power wiring in one, and sensor wiring in the other. 10-15 mm of separation can help a lot with electrical noise, and having two tracks would give me the space to twist the wire pairs.
I'm still going to use the T slots for wiring and cover the wires with the black T slot covers wherever possible, but mostly for aesthetics and tidy snag-free wiring. I can also hide the ugly offset wire splices with heat shrink tubing under the T slot covers.
We should probably be using 10K thermistors rather than 100K thermistors. The additional power is negligible and the 10K thermistors will be more noise tolerant.
The controller should be intelligent enough to sample temperature data when there isn't any motion on that axis, or do long term averaging to eliminate the noise from the very slow moving temperature data.
Twist the wires in pairs. Twisting the thermistor wires can do wonders for noise rejection. Twisting the motor wires in phase pairs should help a lot too. The twisted pairs take up a lot more space in wireway, so that may not be possible, but if you can do it, it's well worth the effort. I'm running a lot of wires through small cable track. Maybe I should have bought the next larger cable track for the big bundle of wires from the extruder and X axis. Even better, if I have noise problems, I might run two parallel cable tracks with power wiring in one, and sensor wiring in the other. 10-15 mm of separation can help a lot with electrical noise, and having two tracks would give me the space to twist the wire pairs.
I'm still going to use the T slots for wiring and cover the wires with the black T slot covers wherever possible, but mostly for aesthetics and tidy snag-free wiring. I can also hide the ugly offset wire splices with heat shrink tubing under the T slot covers.