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shock withstand

ZuzzyZuzzy
in Hardware

Greetings!

First post in here, am now the proud owner of an mms. Worked first time out of the box using the app on a mac air m1 :-) thank you Laura.

For me to keep it working I wonder if there is any data/experience on the device's ability to withstand impact shock? I am interested in sports instrumentation applications where there could be significant impact events. I am intending to mount the device in the rubber clip with a couple of rubber bands around the body.

20 years ago I did something similar mounting instrumentation into the shaft of a golf club, which worked, but initial versions broke the board after about 30 shots! . I dont want to do anything so extreme this time, but I would be interested in any experience (quantitive or qualitative) of the devices ability to withstand harsh conditions.

A typical test would be "does the device survive a repeated 2m drop test onto concrete".

Peter

Comments

  • ZuzzyZuzzy

    So tested this by mounting onto a tennis racquet at the top of the grip, x axis aligned with shaft of raquet. Using the small wristband strap. So some shock mounting isolation there. Recording for 2 hours with >300 ball impact "events".

    Shocks >16g peak on an axis recorded on impact, a bit of limiting. But MMS device quite happy. Good multiple channel data received.

    Peter

  • LauraLaura

    Thanks Peter!

  • ZuzzyZuzzy

    I spoke too soon.

    Data capture has now become unreliable after just a few recordings as above. I have just now definitely connected the cause of this to mechanical shock. For a couple of weeks the data recording and download have been intermittent. Thought it was a software problem initially but have now shown that not to be the case. Streaming of data always works on metawear with real time graphing of streamed data.

    My device will only log data and download provided the device is 'gently' handled during logging. Any significant shocks and the data logging fails. In which case we never get to the session name prompt after download in Metabase. So download is lost. Could be an intermittent battery connection. I notice that there is a rattling sound when shaking the device which I think might be the battery of the MMS or the vibration unit that is not solidly fixed to the mainboard. So could be a power glitch leading to a reset or another intermittent connection (memory chip? seems unlikely)

    Am thinking of trying applying epoxy to hold it all together solidly and get rid of the rattling.

    Hoping it's not a fundamental weakness of the design.

    Once again I wonder if anyone has any similar experiences?

    Thanks

    Peter

  • LauraLaura

    Is the battery getting shorted or are the wires looking like they are about to disconnect? It might help if you had photos.

  • ZuzzyZuzzy

    Hi Laura,


    I took the unit apart, the battery and buzzer are on flying leads and are not held solid within the assembly, so thats the rattling I heard.

    I tried putting a strip of blutak to support and shock absorb.

    Performance has deteriorated, the board will now only connect when the board is slightly flexed. Based of my previous design experience this is symptomatic of a trace cracking or a dry joint or a buried via failure.

    So sadly this board appears dead.

    Either its a defect of the board, or the shock withstand of the board is a bit limited. I guess I will need to put this on hold since as a hobby project I cant afford to keep buying and breaking the sensors. Frustrating since its a lovely piece of design.

    regards
    Peter

  • LauraLaura

    Hi Peter,
    It's hard to see if there is a broken lead in the pictures. I would have to inspect the board.
    If you want, you can send me the board for inspection. I PMed you details.

  • ZuzzyZuzzy

    Well it seems my MMS board has given up the ghost. But many thanks to Laura and colleagues who tried to fix it. I am going to get a new board but I shall be wary of putting in a high shock environment. Will probably try potting with epoxy before doing so. You live and learn!

    Would still be interested to hear any other experiences of successful use of these devices in high shock environments?

  • LauraLaura

    Hey @Zuzzy,
    It was pretty bad, some of the components on your board, including a capacitor had been completely destroyed and removed from the board. I think in your case the board took a very hard shock not typically seen.
    Some folks do cover our boards with additional epoxy to help in these circumstances.

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