[pianotech] flipping a truck

[Mike Spalding]

Ron Nossaman wrote:
> Israel Stein wrote:
>> Something has been bothering me about this. Wouldn't the center of 
>> gravity on a piano mounted on a flipped truck be quite a bit higher, 
>> making the whole thing less stable - if force is applied at the wrong 
>> place in the wrong direction? Granted, a tripod (which is what we 
>> have here) is inherently the most stable configuration, but suppose 
>> sufficient upward force were for some reason applied at one of the 
>> legs - wouldn't it be possible for the whole thing to tip over along 
>> the line formed by the other two legs - given such a high center of 
>> gravity? Now I know that this is not likely, but we have here a bunch 
>> of ignoramuses doing unpredictable things with a piano...
>
> I'm forever amazed that a profession so filled with - recovering - 
> engineers doesn't swamp this sort of question with highly educated 
> answers, all in absolute agreement to four decimal places. But in the 
> continued conspicuous absence of experts, I'll take a non-pedigreed 
> stab at it.
Sorry, didn't think it was worth the effort.  As a notorious mechanics 
prof once said: "It's intuitively obvious to the casual observer.."   
When folks started panicking over how the legs would slide off the truck 
because the little square cups would be permanently affixed to the 
bottom of the arms, I backed off to wait for the smoke to clear.
>
> In my world, the center of mass of an assembly has to be outboard of 
> it's support for it to tip over. So far, I haven't run into an 
> instance where that presumption hasn't proved to be a practical guide 
> to preventing things from falling over. If a piano on a standard truck 
> has to be tilted at 45° (arbitrarily chosen) to tip over, then a piano 
> on a flipped truck, supported at a higher altitude, would tip over at 
> a lesser degree of inclination, say, 40° or so. Even if it were 30°, 
> which is what doing the math instead of speculating is for, it would 
> take a pretty spectacular idiot or committee to make up the 
> difference. While I have no doubt whatsoever that such spectacular 
> idiots and committees exist out there in vast numbers, I submit that 
> the difference between a 45° tip point and a 40°, or even 30° (math 
> verification pending) is way too far past the idiot threshold to be 
> guarded against by a mere 5°, or even 15° (pending the math) 
> difference in an inclination angle already way past rational (math 
> verification impossible). But then there's the question of the legs 
> breaking before the optimal idiot inclination tip point is achieved, 
> thereby robbing the participant(s) of their due glory and immortality, 
> and screwing up the vector calculation.
Just so.  No math required.  See "intuitively obvious" above.
>
> But Then, I'm not an engineer,
Lucky you.  It would have driven you nuts.

Mike Spalding
Not recovered yet