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Old Nov 03, 2011, 11:08 AM
PLD
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PLD-SLOGGER: Servo statistics logger

I've been busy, after some discussions with a couple of people, I've gone ahead and started a prototype servo data/statistics logger.

It may pass or fail on the market, but it'll be curious to play with none the less (and may have other purposes).

The SLOGGER sits between the RX and the servo, it logs at ~20Hz the volts, amps and pulse-width. Depending on the size of the memory chip I install, it can store anything from 30 minutes to 3 hours of data.

Data transfer off the unit requires plugging in a data link lead to the SLOGGER which will then power it up and transfer the data to your PC via USB.

The SLOGGER is 1.1 x 0.7" in size.
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Old Nov 03, 2011, 08:09 PM
KJ4WFG
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This is another dream project for me. It's always a mystery what's going on with a servo. Is it running normal after getting banged around? Is it big enough for the use? Is it bigger than it has to be? Is it getting bound up somewhere in its action? What's the total load they're putting on the BEC? I could go on.

We've had data loggers for everything else for a long time, and pilots who want to know what's happening with their equipment are using them. Now we'll be able to take a peek at the servos. Considering how critical they are to the performance of the airplane (and the cost of high end servos), it's amazing to me that it's taken this long to see this kind of product. Thanks, Paul.

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Old Nov 03, 2011, 08:20 PM
PLD
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I'm surprised as well there's not been a single-channel logger out there.

I won't get too exotic with the development of this unit, beyond volts, amps and pulse-width there's not a lot else to actively chase. I suppose no doubt someone is going to ask for remote telemetry or wifi live-data, though for now I'll stick with the direct data connect option for post-flight analysis.

It's going to be painful waiting for the next few weeks to pass, waiting for all these boards to arrive back from the PCB factory. Might have to design some more things while I wait
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Old Nov 06, 2011, 05:40 AM
PLD
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PCBs have been dispatched from factory... so now about 2 weeks more to wait.
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Old Nov 13, 2011, 07:38 AM
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Will this unit be for a single servo? Would it be cost effective to build a unit that would do three or four servos?

Looking forward to seeing the development on this item.

I have always wondered why the servo manufacturers do not publish current requirements for their servos.

Glen
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Old Nov 13, 2011, 08:03 AM
PLD
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Glen,

It'll be a single-servo unit. It is possible to do multiple units on a single board but I must admit that the cost goes up quickly and the overall complexity and size of the board can become a bother.

The main focus of the SLOGGER is to be more of a diagnostics tool as opposed to a permanent installation.

I think a lot of us would be happier if we knew we could trust things like the stall current specifications on servos; those being the most crucial for a worst-case management/preparation development.
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Old Nov 17, 2011, 09:15 PM
PLD
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Circuit boards arrived today. Might have the first prototype going by Monday... though I just realised I haven't pre-ordered the memory chips for it.
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Old Nov 19, 2011, 06:42 PM
KJ4WFG
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Put my initials on SLOGGER S/N 00001. I ordered eight SFUSE1's this morning(all the site would let me order), and I need SLOGGER to verify what resistance fuse to put on SFUSE1. Instead of relying on the mfg published stall current for the servos, I want to measure the actual current draw under load in the air. I'll put the control surface through the most stressful maneuvers that I can handle well and see what the servo draws. Then go to the fuse operating curves and select a fuse that'll take it out quickly in an unusually high current but give it room to work under normal high work loads. This is gonna be cool. Rev it up, Paul
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Old Nov 19, 2011, 08:28 PM
PLD
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Hoping that the memory chips arrive tomorrow, then I can get straight to doing the SLOGGER and firmware. Did you want me to hold the shipment of SFUSE's until the SLOGGER is done? I'll be able to combine the postage which would save you about $10.
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Old Nov 19, 2011, 08:30 PM
KJ4WFG
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Please. More Christmas funds. Hhmmm.......
Thanks
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Old Nov 19, 2011, 08:31 PM
KJ4WFG
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Wanna throw some .25 amp fuses in there too?
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Old Nov 19, 2011, 08:43 PM
PLD
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Quote:
Originally Posted by modbuilder View Post
Wanna throw some .25 amp fuses in there too?
Won't be a problem at all.
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Old Nov 20, 2011, 09:17 PM
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thanks.............R
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Old Nov 20, 2011, 09:32 PM
PLD
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Memory chips arrived today... these are 256Kbit units, hopefully enough for a couple of hours of logging. It's going to take a few days/week for me to do the firmware and probably longer to make a nice application for the PC (though a spreadsheet or data logger such as gnuplot would work).
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Old Nov 21, 2011, 01:37 AM
PLD
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First build...

Here's the first build of the SLOGGER.

A couple of points;
  • I'm only powering it via a 2S lipo while I do the initial programming
  • The bulky "normal" resistor is only being used until my stock of proper 0.1R flat surface mount units arrive

The unit is quite small, certainly no larger than a 15A ESC these days and quite a bit lighter.

The development stages will be;
  1. battery voltage detection
  2. current measuring (via shunt)
  3. servo pulse detection and storage
  4. clock synchronising (I might have to pick a different crystal value so that I can get proper timing and high speed serial
  5. external EEPROM storage of all the data
  6. serial comms
  7. dumping of the data from the EEPROM to the serial
  8. write PC side software

The first few items will occur quickly... the PC software will take a bit longer.
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