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Thread: Servo requires "tapping"

  1. #21
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    Quote Originally Posted by RalphTrimble View Post
    I remember that thread and I could not see the value of longer Cat5 runs, lol.

    I have been using Kuman MG90s servos and have had good results with them, They are all metal geared
    Heatermeter Builder. Adapter Board v6.3, Heatermeter customizer.

  2. #22
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    I too had the shakes when my damper was controlling around the 0-10% open position. I turned on the 60hz filter and problem now gone. I have very smooth damper and control action now.

  3. #23
    TVWBB Honor Circle Bryan Mayland's Avatar
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    I spent a few hours testing various configurations of booster circuits and wire lengths and have come to the conclusion that no booster makes a difference here.

    Booster Circuits
    • None - direct from Microcontroller
    • Voltage Booster - HeaterMeter v4.2/4.3 circuit with a 1k pullup to 5V on servo signal
    • Voltage Booster + Inline Diode - Same as voltage booster but with a diode after the boost
    • Current Booster - common collector amplifier / emitter follower / Ralph's linked circuit


    Servo Connections
    • Directly to HeaterMeter (<100mm)
    • End of ethernet cable (~2m)
    • Long run simulation. This uses the 2m ethernet cable but also adds a 10 ohm resistor to the servo signal after the booster to simulate a longer run (~75m).


    Of all the connections, the long run was by far the most problematic, with the servo going nuts all the time so most of my testing was done with this setup. The Current Boost and None setup did equally well. Both Voltage and Voltage + Diode did poorly, but only mildly better than the other circuits but I'd say none of them were acceptable in terms of performance. The Current Boost puts out a 2.7V signal with a 0.24mA current draw during the pulse followed by a -0.20mA dip as the pulse is discharged. The None was similar with a 3.3V signal, 0.24mA current, and a discharge that maxed out my current meter (-1.30mA). Voltage Boost put out a 5V signal but used almost twice the current 0.4mA and the same maxed discharge. All three had a high inrush current which maxed my meter >1.30mA.

    I then spliced in a splitter to the servo end of the output and installed a socket for placing a capacitor on the power lines at the servo end. First capacitor, 10V 470uF, all circuits had zero problems. 10V 220uF - zero problems, 10V 100uF - zero problems, 25V 47uF - zero problems, 25V 22uF - zero problems. You can see a trend here. Then I tried 50V 0.1uF which had zero problems with the Current and None boosts, but showed rare glitches with the voltage boost circuit. Placing any of these capacitors on the HeaterMeter side of the 5V line had no beneficial effect. Without the capacitor, the 5V line measured at the servo varied from 4.14V to 6.18V.

    Conclusion: No boost circuit works perfectly, but the Voltage Boost which is integrated on the HeaterMeter 4.2/4.3 boards is the clear loser in all testing. The best solution is to place a capacitor on the servo's 5V/GND pins as close to the servo as possible. Based on these observations, future hardware designs will certainly not use the Voltage Boost circuit. The Current Boost circuit as it did not show any beneficial effect above the None and given that the peak current draw and pulse current draw are the same with both of these, the Current Boost will probably not be used either.
    I'm that HeaterMeter guy what ruins everybody's free time.

  4. #24
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    I didn't go about it in a scientific manner like you did, but my cable is about 50ft, my servo spazzed like crazy. I added the current booster and the servo works perfectly. I put the current booster in and out of circuit many times and this was completely reproducible. With the voltage booster my servo works fine as well, though some Tower Pro models do jitter a bit while other servo's work fine. I leave my HM and RD3 connected and powered 24/7, been over a year maybe two, so I know the servo is not overheating, I also know without some sort of servo booster my servo would be DOA on this 50ft cable.
    I created the Roto Damper, RD3, HMv4.2 sliding back case, "air-burner" and the "ping-pong" valve in my quest for delicious "set and forget" BBQ.

  5. #25
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    So Bryan, the results using a capacitor across the supply leads on the servo is very interesting and I will probably add a 25v 100uf cap from my parts bag to the blower/damper I am using. Did you try turning the filter on and see if you could get the same results as you would by adding the cap. Curious to see if anyone else had the same results that I did.
    Glad your safe and that Irma left you with hopefully minimal damage. Hope the others in your state get back to enjoying their lives as they were prior to the storm real soon. Were thinking about you out west.

  6. #26
    TVWBB Honor Circle Bryan Mayland's Avatar
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    Yeah Ralph am not at all doubting the effectiveness if your circuit for your build-- it clearly works for you. I am just unable to reproduce the results quite as well. It seems odd considering the current needed is so low (1/4 milliamp) that a current boost can help. It must have something to do with the impedance of the circuit responding to the turn on, or the sharpness of the pulse edges. I couldn't see any skew of the signal in any configuration, although I was measuring closer to the HeaterMeter and not at the servo end for the pulses. Before I disassemble the test rig I am going to do that now that I think about it because the pulses might look wonky on the far end of the cable.

    Gary, I did not try the 60Hz filter. The filter just changes how the analog inputs are read, trying to match them with the period of the AC frequency so it seems like a strange coincidence that it made a difference in your case.
    I'm that HeaterMeter guy what ruins everybody's free time.

  7. #27
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    I think you using a pure resistive load to simulate 50ft of wire is where the difference lies.
    I also forgot to mention that the degree of malfunction of the servo went up with the size of the blower being used, and the effectiveness of the current booster did equally well to correct servo malfunction when using larger blowers.
    I created the Roto Damper, RD3, HMv4.2 sliding back case, "air-burner" and the "ping-pong" valve in my quest for delicious "set and forget" BBQ.

  8. #28
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    Decided to try this out with a wonky servo I had. I put a 47uF cap across the servo power supply (fit nicely in the LAN connector under the cap) and it took every bit of "wonkiness" out, and it runs very smooth.

    I'll be building all my dampers with this mod, now.

  9. #29
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    Will,
    If you can, will you post a picture of how you attached the capacitor to the lan connector.

  10. #30
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    Quote Originally Posted by Gary V View Post
    Will,
    If you can, will you post a picture of how you attached the capacitor to the lan connector.
    Pretty straight forward ...


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