Servo requires "tapping"


 
Bryan Mayland said:
The size should be fine, generally more is better when it comes to power smoothing, although too much can create resonance instability with the power supply technically. Are you putting the capacitor across the 5V/GND lines or the SERVO/GND lines? It should be 5V/GND. I think I've tried a capacitor that large before and it worked but it has been a long time since I tested it and I believe it was with an SG90.

Edit: Also make sure the capacitor polarity is correct, although if it were backward I think it would just reboot over and over again.
Click to expand...

I wired it just like in this picture:
https://tvwbb.com/showthread.php?71...t-tapping-quot&p=791838&viewfull=1#post791838
 
Hello

I recently built a HM board (4.3) and the RDTC board too. The servo and blower work fine with a 6ft cable but when I go to 25 or longer when the fan gets going the servo losses its mind. But if I disconnect the fan the servo works fine at longer lengths. Would I need this booster circuit or is it just my PSU isn’t good enough (says 12v/2A but is of no discernible quality). Any advice would be great.
 
I would try another power supply, when the servo flakes out as the fan ramps up that can indicate a brown-out situation. you could also try another CAT5 cable. If it is a home made cable you might re-crimp the ends...
My cable is about 50ft long, goes from my deck through the basement into my kitchen, has been working great for years now...
You could also try putting a capacitor across the servo leads as detailed in other threads in the forum, however, I do have caps built into the RDTC board for this purpose and I have never needed one on my servo.
 
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MartinB said:
Most temp probe wires are 3-4'. Even 6 is a lot.
Why do you think you will need 25' cable?
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Sorry I should have made it clear it was the Ethernet cable to the rdtc board and not the thermocouple or thermistor cables. I want to leave the HM indoors and run and Ethernet cable outside to the RTDC.
 
RalphTrimble said:
I would try another power supply, when the servo flakes out as the fan ramps up that can indicate a brown-out situation. you could also try another CAT5 cable. If it is a home made cable you might re-crimp the ends...
My cable is about 50ft long, goes from my deck through the basement into my kitchen, has been working great for years now...
You could also try putting a capacitor across the servo leads as detailed in other threads in the forum, however, I do have caps built into the RDTC board for this purpose and I have never needed one on my servo.
Click to expand...

It’s a premade cable. But I’ll be using my outdoor rated CAT6 and crimp the final cable. So I should try to hunt down a 12V/3A or higher psu? The one I’ve got is 2A. I guess I should measure the amps as the fan spins up to confirm.

I tried a capacitor last night (16V 100uf) but it didn’t appear to help. Thanks for the advice.
 
So I upgraded to a 5A PSU and it helped by I still can't run the fan at full and the servo not jitter on a 50ft run. I can only run it at about 45% max speed before the servo jitters. I don't suppose there's a way to power the raspi separately? Like use the USB power on it directly (offload some of the work) and leave the external adapter for the rest of it? I'm using a pi zero with wifi.

Running the fan at half speed isn't the end of the world, would just take longer to reach temp.
 
I can't recall if you tried a different servo? That may be worth a shot... With such a long cable the quality of the ends and crimp are very important, I've had some cables perform well and others not. I have hand crimped my cable, its about 50ft long and has been working without jitters for years now. (It is older CAT5e solid 24 gauge cable, this week I wired a network with a new spool of CAT6e cable and the wires seemed very thin compared to what I have at home) If you hand crimp make sure you follow the standard CAT5 wiring scheme, when putting this together I found if you choose wires at randum there will be crosstalk interference. I spent a lot of time working out the wiring scheme that works best, you need keep certain wires in twisted pairs to cancel crosstalk.

That said, on my last two cooks I have had a slight bit of jitter, which is unusual. I checked the cable and CAT5 jack at the RD3 and it looked good so I chalked it up and assumed the servo which has been out in the weather and powered on for close to two years is just failing. I haven't gotten around to swapping out the servo yet, I will report back when I do if my jitters go away.

It is also possible that a firmware change of how active the servo is may be involved here (how small of increments the servo moves in, rest period etc), not sure if Bryan made any changes in the servo movement lately? I am running the snapshot release loaded a couple weeks ago. Previously I have had a very long run with no servo jitter on this same cable. It is also possible that I need to recrimp the outside end, that needs to be done every couple years of being exposed to weather. So I have a little jitter troubleshooting to do right now myself, will report back if I come up with any unusual findings.

When I first started experimenting with long cables I had trouble with the servo flaking out badly so I put together a servo booster circuit which eliminated the issue. I posted a thread about it at the time which can be found here, there is a video there showing an original roto damper with and without the booster. You will hear some jitter (buzzing) in that video, this is due to drag on the servo from wires, a problem enherent with the original RD design, the RD3 eliminates moving the blower and wires to eliminate this drag on the servo and related jitter. I shared my findings with Bryan and asked that he add it to the HM build, he did end up adding a different version of a servo booster on the HM board which is still present today. However, in my experiments with a long cable my circuit was more effective. If you feel like experimenting you can build it up pretty cheap. (you can use it inline with the CAT5 cable and booster that on the HM board without issue)
ServoBooster.jpg
 
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Yeah CAT6 is more tightly wound so it's technically longer internally than the same length of cat5. Using a cat5 cable helped me a bit too. I think my best chance is finding a thicker gauge wire ( CAT5e spec says up to 22AWG is acceptable but finding it is easier said than done). I may give that booster circuit a shot. Or just break out the power lines entirely and run them separately through some thicker wire.

Thanks for all the feedback. Very much appreciated.
 
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