Pressured air cooling controlled with servo and ball valve
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ok understandable, I am doing something similar but I am coming off a compressed air line from outside and using a pressure transducer to regulate pressure to the hotend, and print cooling. I am just waiting on the transducers to come in.
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@chainbreaker2012
Exactly, I would like to control the servo position based on fan speed.Since this already kind of works without any additional electronics on the Duet, it is rather a software issue. My problem is, that the fan S parameter (0-255) does not correspond to the servo angle. The servo can be controlled with an S parameter between 44 and 141 which correspond roughly to 20-80% fan speed.
Therefore, I need to adjust the given S parameter of the fan output, so that at 0% fan speed the given S parameter is for example at S 44 (0° Servo angle) and at 100% fan speed it is at S 144 (180° Servo angle).
Cheers Max
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@MaxGyver can you not use the L and X commands of M106 to do that?
Lnnn Set the minimum fan speed (0 to 255 or 0.0 to 1.0) when a non-zero fan speed is requested. Xnnn Set the maximum fan speed (0 to 255 or 0.0 to 1.0) when a non-zero fan speed is requested. (supported in RRF >= 2.02)Owns various duet boards and is the main wiki maintainer for the Teamgloomy LPC/STM32 port of RRF. Assume I'm running whatever the latest beta/stable build is
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@ dc42 maybe an option could be added to the M106 command, similar to the R value in M453
Rbbbor Raaa:bbb RPM values that are achieved at zero PWM and at maximum RPM. Used to convert the S parameter in M3 and M4 commands to a PWM value. -
@jay_s_uk said in Pressured air cooling controlled with servo and ball valve:
@ dc42 maybe an option could be added to the M106 command, similar to the R value in M453
Rbbbor Raaa:bbb RPM values that are achieved at zero PWM and at maximum RPM. Used to convert the S parameter in M3 and M4 commands to a PWM value.Yes, this would solve my problem.
Cheers
Max -
As an alternative to my Ball Valve+RC Servo design, I have ordered a PWM capable proportional control valve. The advantage of the Proportional valve is that it is basically plug & play and has less moving parts. But just like the servo, it has a specific PWM range from 300-400 Hz for 0-100% flow. So my Problem remains the same...
@dc42 would it be possible to add an R value to the M106/M950 command to control the PWM frequencies that are achieved at zero PWM and at maximum RPM similar to the R value in M453?
Cheers
Max -
The data sheet at https://www.burkert.com/en/Media/plm/DTS/DS/DS2863-Standard-EU-EN.pdf doesn't seem to match your decription.
That just refers to PWM and the figure on page 8 shows a pretty linear repsonse from about 0.1 to about 0.9 input - probably more linear than any fan, so I don't believe you do have the problem you think you do - surely you just use this as a 24V fan, with a 400Hz PWM? You could put 0.1 low limit on it so it opens immediately you have any non-zero demand.
I do note that I don't understand the X axis scale on that graph, because it's a 24V 420mA coil. Also I'm assuming that response to PWM will be similar to the response to whatever that scale is indicating.
Where are you seeing something that suggets you need to vary PWM frequency? M950 already lets you specify teh frequnecy and then the standard fan control will vary duty.
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Thank you for your feedback. I think you are partly correct.
I have tried setting different PWM frequencies in the M915 command. The valve behavior does not change much. Although on higher frequencies (Q>4000) the valve stopped whining, so I am going to stick to those.
This is my recent Fan/Valve config:
M950 F1 C"1.out1" Q-1 M106 P1 S0 H-1I have good control over the airflow with a fan speed from 78% (valve closed) to roughly 90% (valve fully open).
Cheers
Max -
@MaxGyver said in Pressured air cooling controlled with servo and ball valve:
78% (valve closed) to roughly 90% (valve fully open).
Look at the M106 L and X parameters to set the min and max range to match your usable range. That should scale the S parameter to make S0 to S255 within your usable range.
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I have already tried this. The L and X factor of M106 will not scale the range but rather set the minimum and maximum fan speed.
With this configuration the valve will stay in the same slightly open position at a fans peed of 5-80%. So I still only have real control over the flow from 80-90% fan speed.
M106 P1 S0 H-1 L200 X255Cheers
Max -
@MaxGyver My mistake.
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@MaxGyver said in Pressured air cooling controlled with servo and ball valve:
Although on higher frequencies (Q>4000) the valve stopped whining, so I am going to stick to those.
This will for sure change the valve response characteristics. Perhaps this is why the valv response is not as stated in spec.
400Hz is the way to go.
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@BoA The valve response characteristics do not change with the PWM-Setting. I have the same response with 300, 400 or higher Hz. Only with high Hz the valve is noiseless.
Cheers
Max -
@MaxGyver how is this valve working out for you? I'm looking at a similar setup but using a compressed air source instead of an aquarium pump.
Have you put a flowmeter after your solenoid to determine how much air you are delivering and able to control the airflow?
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Hey @lael,
yes the setup is working well,
I am using this pump by the way.
It has more than enough airflow, good pressure and is not too noisy.
I am switching the 230V power for the pump with a relay.The valve is also working good so far. Although I have not figured out how to map it correctly to get a range of 0-100% airflow like mentioned in my previous posts.
Right now I am printing with PLA where I have it fully open all the time anyway.I have tested the airflow with a flow meter. At the hotend I have an airflow of around 20-25l/min. This reduction is mostly due to the 4 mm internal diameter of my tubing. But so far the airflow is sufficient.
-Max
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@MaxGyver Good to hear! That is quite a lot more airflow than Berd Air will supply. What is the max and min airflows you can control it to?
So for the wiring configuration you have a relay in line on the PWM fan output that triggers the Relay for 240V to the pump? That way when the fan would be on the pump turns on?
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In terms of part cooling at the hotend - this guy: https://twitter.com/brendonbuilds/status/1313914876922912768/photo/1 has an interesting setup. Looks like a resin printed part, but a 6mm aluminium tube should be able to be bent into the same design.
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@lael I can control the flow from 0% to 100%. The problem is that this range corresponds to the area of 80-100% fan speed on the duet. My workaround is to set the minimum fanspeed in my slicer to just over 80%.
Since I am also cooling my hotend with the air pump, I have set up the relay to trigger when the hotend reaches a certain temperature.
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I can see how that would create some frustrations with slicing. Do you have any photos of your hotend cooling setup - that sounds neat!
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@MaxGyver I wonder if the control restriction you are seeing is related to the lack of air pressure running through the valve. If you take a look at a similar, but different valve here: https://docs.rs-online.com/02fd/A700000006738966.pdf (SMC, amperage controlled, not PWM), you can see that the operating pressure has a direct correlation to the operating range of the valve, and that with too low an air pressure, the total flow (lpm) will be reduced.
It also seems that a larger bore is more effective with a lower pressure. (What bore size is the model you got?) I would guess, without doing the math in the burkett data sheet, that their valves would have similar / identical properties.
So for the SMC model at a bore size of 4mm and pressure of 0.04Mpa / ~5psi you would expect to see the total range of flow starting at 230mA and wide open at 320mA/330mA, and with a flow of 0-30Lpm. I wonder if that behaviour is why you are seeing the PWM control in such a narrow band?
