Subject:
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Re: Surveying MTBF of Edu NXTs
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Newsgroups:
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lugnet.robotics.nxt
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Date:
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Fri, 23 Feb 2007 21:26:42 GMT
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Viewed:
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13848 times
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In lugnet.robotics.nxt, Edwin Pilobello wrote:
> I have 11 commercial (C) and 25 educational (E) NXT sets. The 11Cs are doing
> fine after about 4 battery changes. They have been in use since July 2006 for
> about 60 class hours.
>
> I'm sure there's a more empirical way to calculate how much run-time 4 sets of
> batteries can produce. My off-the-cuff estimate is that the 11C NXTs have at
> least 2 hours of run-time on them.
>
> By comparison, 1 of the 25E NXTs is now dead after less than 10 minutes of
> run-time. Another is showing signs of senility out of the box. I suspect that
> NXT will die soon.
>
> Does anyone have a better idea of what the mean time to failure is for NXTs?
> I'll have to tell our administrators what to expect out of their $8,750
> investment.
You should be able to estimate time-to-failure in the presence of your censored
data; people do this all the time in engineering and cancer and many other
fields.
Steve H seems surprised at the fact that any NXT died and I must say that I am
surprised as well. Perhaps TLG would replace that NXT for you if you were to
ask...
(I still have handheld electronic games from the late 1970s and they work just
fine, in particular, Coleco Electronic Basketball. My kids think it is fun, in
a quaint and quirky and disparaging sort of way.)
If you assume an exponential lifetime model to the NXTs, then you have one or
maybe two observed data points and 34 censored observations. The statistician
in me (who sometimes competes for space with the developing Alien baby) thinks
that you don't have much useable data. My current statement to management is
that their investment should be expected to last many years, barring the
short-life failure in approximately 5% of the devices (which hopefully will be
replaced!). You could also do some (nonparametric) Kaplan-Meier estimates of
time-to-failure but with only 1 or 2 failures, estimating anything other than
probably the 5th percentile will likely prove futile.
Rafe
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Message has 1 Reply:
 | | Re: Surveying MTBF of Edu NXTs
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| First, let me repeat the request for specifics. I *have* had some reports of indivdual sensors failing (and being replaced by LEGO), as well as the rare motor that seems a little bit to high in internal friction (and, again, at least addressed by (...) (18 years ago, 23-Feb-07, to lugnet.robotics.nxt)
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Message is in Reply To:
| | Surveying MTBF of Edu NXTs
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| I have 11 commercial (C) and 25 educational (E) NXT sets. The 11Cs are doing fine after about 4 battery changes. They have been in use since July 2006 for about 60 class hours. I'm sure there's a more empirical way to calculate how much run-time 4 (...) (18 years ago, 23-Feb-07, to lugnet.robotics.nxt)
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