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Cable management and other noob questions.

Posted by JumpJetJones 
Cable management and other noob questions.
June 22, 2018 02:52AM
Hello everyone,

First I would like to thank everyone here for being so willing to share their knowledge and experience. I have been reading these forums for a couple of months now, and I never knew there was so much I needed to know smiling smiley

I am working on a scratch built Phranken-printer inspired by printers I've seen in my kids' classroom, and videos I've seen on YouTube. I'm currently trying to work out cable routing, and I'm wondering how careful i need to be running power lines next to signal lines. For example, If I bundle the power lines for the hot end cartridge heater in with the leads from the hot end thermistor and the motor cable for the Y axis stepper motor, is there any risk that spurious signals generated by one will affect the others? Likewise, if I bundle the motor lines fore the X axis, Y axis and/or the extruder steppers together, is there any chance that cross talk between them will generate unwanted signals that might cause the motors to behave unpredictably?

Another thing I'm concerned about is the length of the motor wires themselves. The printer I'm building has a printable volume of roughly 25 centimeters width by 30 centimeters length by 45 centimeters height, -- yes I know that sounds weird, but the dimensions are determined by the fact that I'm using 80% or more in salvaged and/or reclaimed parts.-- As a result some of the motor lines are going to be a meter -- more or less -- in length. Will that change some of the configuration parameters for those stepper motors, thermistor, and/or end stop switches?

I'm using the more or less standard Arduino 2560 with the RAMPS 1.4 shield and A4988 drivers. Why? because it's what I had. I understand that the 12 volt connector for the second extruder can be used to run a fan. Is this the fan that cools the hot end mount and prevents the filiment from melting were you don't want it too, or is it the fan that blows on the work space and cools the plastic post extrusion? Can you attach 2 fans to the 1 output and do both? Could the thermistor for the second extruder be used to control those fans?

The PSU I am using is an EVGA 850BQ ATX, I know its overkill, but I had one gathering dust on a shelf. Interesting side note, ALL of the wires coming out of an EVGA PSU are black, and I do mean ALL of them, so telling me to look for the green wire on the ATX plug is a bit like sending a 2nd luey out for "frequency grease" if you take my meaning smiling smiley This PSU is capable of supplying 70 amps on the +12 volt rail, weather the 5 volt rail is loaded or not, and I could certainly run a couple cooling fans off the periphreal connectors, but doing so means the fans are on whenever the PSU is on. Can that be a problem? Is there any way to power the fans from the PSU and still control them from the ramps board? I'm in southern Michigan and so far the only SSR's I can find locally are $45. That's a bit outside my price range at the moment. I could easily enough wire in an on/off switch for the fans, but I don't think that would be much better.

All feeback gratefully accepted,

Re: Cable management and other noob questions.
June 22, 2018 08:09AM
The chances of motor leads talking to each other is near zero. Routing high current leads (motors, heaters, etc.) alongside small signal leads like thermistor wires is potentially a problem.

You can minimize coupled noise between cables that run close to each other by twisting the pairs of wires together. For example, motors typically have 4 leads connected to two coils in the motors. Twisting the pairs of wires for each of the coils helps prevent them from generating noise that might find its way into adjacent cables. Twisting thermistor wires helps prevent them from picking up noise from adjacent cables. And, when possible, physical separation of noise generating cables (motor leads, heaters) and small signals (thermistor leads) is a good idea, but not always practical. The extruder heater leads, motor leads, and thermistor leads usually have to run close to each other because they are all in one bundle of wires that goes to the extruder carriage. That's when twisting the individual wire pairs becomes very important.

If you're making cables to connect to your motors or thermistors and wondering how to accomplish the twisting, it isn't hard to do and is very quick if you have an electric drill.

Video- wire twister

Another way to induce noise into wires is to share ground and power supply wires among multiple devices by daisy chaining the devices together. It is best to run power and ground leads all the way back to the power supply when possible.

Son of MegaMax 3D printer: [www.instructables.com]
Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]
Re: Cable management and other noob questions.
June 22, 2018 12:14PM
In essence you want to distinguish between power-carrying and signal-carrying conductors. Cables that carry power (power wiring, motor wiring, heater wiring, fan wiring...) are generally noise-producing, and are not sensitive to EMI. Cables that carry signals (limit switches, sensors, thermistors...) produce negligable electrical noise, but might be sensitive to interference and should be kept away from power wiring.

Electrical interference is more or less irrelevant for the typical 3d printer. If you run thermistor wires next to the heater and stepper wires for a meter or more you might start to see degraded performance, but thats as bad as it gets.

Proper grounding as previously mentioned is also important, but if you are using a single-board controller its more or less handled.

Its more important to ensure that moving wires won't catch on anything, and won't crack or otherwise suffer damage over time.
Re: Cable management and other noob questions.
June 22, 2018 12:59PM
Noted, and Thank you both for the quick reply.
Re: Cable management and other noob questions.
June 23, 2018 06:16AM
Both my printers have the heater/thermistor/extruder stepper bundled right next to each other in a single cable wrap with no particular precautions taken to prevent noise issues, so far no noticeable noise problems.

As for running two fans off one connector on the ramps, I'd say it depends on the fan. That being said, I see no reason why the heat sink fan can't be connected straight to the power supply. Run your part cooling fan from the ramps connector since that's the one you actually want control over.
Re: Cable management and other noob questions.
June 25, 2018 06:45PM
I was considering that option for the fan connection.
Re: Cable management and other noob questions.
June 28, 2018 11:49PM
Stupid question, short of using an oscilloscope, Is there a way to verify the proper operation of the A4988 driver chip? I have identical 1 amp motors for my X and Y axis. The divers for both axis read 0.57 volts.. The Y axis works perfect, the X axis motor chirps back and forth. Near as I can tell the configuration in marlin for both motors is identical. I thought my X axis belts might be too tight, so I loosened them up a bit and it worked for a couple passes. I swapped motors cables and everything I could think of except the driver chip. The problem stays with the X Axis. Is it possible I could have damaged the X axis driver because the belts were too tight?
Re: Cable management and other noob questions.
June 29, 2018 07:26AM
Swap the X and Y motor connections at the board. If the problem moves to the Y axis, the X driver (now connected to the Y motor) is the problem.

Are the driver boards made by different companies? If so they may have used different value reference resistors so the current may not be the same even though the Vref is the same. You might be able to see a difference if you have a microscope to look at the driver modules.

This sort of crap is one of the things that motivated me to get a 32 bit controller about 4 years ago. Motor current is set in the config file. The other huge motivator was no longer having to deal with the Arduino IDE that suddenly can't compile the controller firmware every time they upgrade the IDE.

Son of MegaMax 3D printer: [www.instructables.com]
Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]
Re: Cable management and other noob questions.
June 30, 2018 06:36PM
I did that, The problem followed the x axis driver chip. replaced the chip problem solved. now to tackle the mechanical issues with th Z axis smiling smiley
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