Best posts made by Iamturbo1978

@MegaAndy, Thank you for bringing this up, I have been trying for months to remove an issue with blobbing(or zitz). I've tried everything I could think of, and I tried everything others suggested. But I could not get rid of my problem. Then I changed my microstepping from 16 to 128, and the problem went almost away. I still have to do some tuning, but so far I am liking the results.

Hello everyone,

I came up with an idea that would automatically keep my stepper motors cool, and I want to see if it would work before I put any effort into it.

I currently have heatsinks and fans on my stepper motors. They work great, but the fans are on when there is no need to have them on. So I came up with the idea of having the DuetWifi control the fans when the motors got above a set temperature. Just like the hotend fan. I would have thermistors on each motor, and a fan that is linked to each thermistor. That way if a motor started to get warm, the cooling fan would kick in. Plus it would allow me to see if a motor is getting to hot since the temperature would be displayed on the web control.

I would not be buying a Duex2 or Duex5 for this since I don't have the need for the additional stepper drivers and/or the heater MOSFETS. I would using the Duex5 schematic as a reference for designing my own board. I would use all the exact same parts as the Duex5, just without the extras I don't need.

So I am asking all the Duet gurus... Could I use the Duet to monitor some thermistors and control some fans to keep my stepper motors cool without having the fans on all the time?

thermistors

Thanks
TC

P.S. One option I did start on, is making a circuit using a comparator that would turn on a fan when the temperature went above a set level. I would do this idea if the Duet idea would not work.

@chrishamm thank you so much for the reply. It makes total sense why not to load the config automatically. I now understand what I need to do. Thank you.

@doctrucker good point. Hopefully, by putting the encoders as close to the print head as I can, a good majority of the "slop" in the system could be filtered out. In theory, the closed loop should notice the wobble of the head, and make corrections.

@wilriker Please understand, I am in no way an electronics pro, but from the questions I have asked in my life, and the experiences I have had, I think I can answer you correctly.

Peak-to-peak ripple really matters for sensitive systems. Like video/display, audio, high frequency microprocessors. But stuff like LED's, motors, fans, hotends, etc... dont care about the ripple. Ripple only really applies for power supplies. Within a power supply (non-linear kind), there is a coil called an inductor. The power supply will charge and discharge that inductor to either boost or buck the input voltage (depending on the setup). The charging and discharging of the inductor will create little spikes. Those spikes are ripple. Understanding ripple can be complicated. The duet's PWM output doen't have an inductor to charge. So the ripple should be very low, to almost no ripple at all.

Hope that helped

Thank you everyone for your insight. Because of your input, I think I am going to go forward with doing a closed loop system for a couple reasons... One, to add one more example of using a closed loop system on a FFF printer. Two, move out of my personal comfort zone doing the designing and planning.

@dc42 Thanks for bringing that up. I wanted to say there are 2 pulse fans. My Delta (company) fans are all 4 pulse per revolution.

@wilriker I'll try to make this as simple as I can, hopefully this will help.

A PWM signal only has 2 states, "HIGH" and "LOW". for this example the voltage does not matter. It could be 12V, 5V, 3.3V etc... We don't care about the voltage right now, only the PWM signal.

The PWM frequency is the number of PWM cycles in one second. If the frequency is 100Hz, then there are 100 PWM cycles in one second. Meaning, that each PWM cycle is only 0.01 seconds (10ms) long.

The duty cycle is the ratio of how long the signal is high to how long it is low.

If we have a duty cycle of 50%, the signal would be high for 0.005 seconds (5ms), then low for the remaining 0.005 seconds (5ms). If we set the duty for 30%, that would be 3ms high and 7ms low. and if we set it to 90%, that would be high for 9ms, and low for 1ms.

The common way for a PWM cycle is to start high, wait the amount of time set by the duty cycle, then go low for the remaining amount of time. Not everything follows this way, but for this example, we are not going to worry about the other ways.

Now, lets say our filter is tuned to only look at a single 10ms (100Hz) PWM cycle. It would only see the signal being high for sometime, then go low for sometime.

But now lets change the filter to look at a 9ms (106Hz) PWM cycle. It would see the high like the last filter, but the low would be shorter than the other filter.

Lets set the duet duty cycle to 50%, and the frequency to 100Hz (10ms cycle). The duet would make the signal high for 5ms, then low for 5ms. Now we add the 106Hz filter. The filter is only going to see 9ms of the PWM cycle. So that would be 5ms high, then 4ms low. That would mean the signal is high 80% of the time ((4ms/5ms)*100). That means, even though you set the duet to 50%, your fan would see 80%.

Capacitors are like water towers. They store a charge, and depending on there size, they can store a little or a lot of charge. That stored charge takes time to discharge. Larger caps take more time to discharge, just like water towers. Everytime the PWM signal goes high, the cap gets charged. And every time the signal goes low, the cap gets discharged. How much discharged depends on the load, your fan for example. If the cap cant discharge most of the energy before the next PWM cycle, the cap gets recharged before it can discharge. If you keep putting in a 80% PWM duty cycle into a cap, but only using 40% of the energy, the cap would be fully charged in only 2 PWM cycles or 20ms. That is why your fan stays on no matter what duty cycle you set. And that is why the lower frequency helped, there was more time for the cap to discharge.

The advice I gave you before was me trying to get what you had on hand to at least help you. Without some kind of feedback from the fan, and a circuit to monitor and adjust the PWM on the fly automatically, you are not going to be able to get a direct correlation between the speed you set, and the actual speed of the fan.

What I did is with my old ramps board is is found a R-C combination that removed the PWM noise from the my fan using the smallest cap I could use. I used a 100uF cap, and a 10Ω resister on a fan that has a 0.25A rating. If my fan used less power, I would have used a smaller cap.

Hope that helped.