Would like to monitor turning speed of my shaft. I understand there is a
device that mounts on shaft hub and counts number of nuts or bolt heads that
pass or some sort of reflection from the turning shaft. Anyone familiar
with this instrument???
Yes. It is called a tachometer.
Here is you to build your own for $30.
Obtain a bicycle speedometer by negotiation with your kid. Epoxy the magnet
on to the shaft coupling. Fashion a mount for the sensor (sheet aluminum
worked for me.) Run some twisted pair up to the display (about 40' in my
case). Fuss with where/how to best mount the display for six months.
Calibrate the instrument using the instructions but backwards: ie. you are
looking for a certain calculated number to appear, so you fuss with the
multiplier constant at a given engine RPM X your reduction ration to give
the number you are lookin for.
While you are doing this, you realize that the reason you are doing it is to
calculate a DR speed. Flash. So you fuss with the constant to have the
instrument read your DR speed directly.
BTW, now you have an instrument which aggregates total shaft miles/hours,
trip miles/hours,etc. etc.
For $30.
Now, how bad is that for a marine instrument?
Richard
PS Mine is dead accurate to the measured mile speed from about 3kn to 7.65kn
at which point it curves up from actual speed (hull length effect) at a
predictable rate.
Would like to monitor turning speed of my shaft. I understand there is a
device that mounts on shaft hub and counts number of nuts or bolt heads that
pass or some sort of reflection from the turning shaft. Anyone familiar
with this instrument???
Yes. It is called a tachometer.
Here is you to build your own for $30.
Obtain a bicycle speedometer by negotiation with your kid. Epoxy the magnet
on to the shaft coupling. Fashion a mount for the sensor (sheet aluminum
worked for me.) Run some twisted pair up to the display (about 40' in my
case). Fuss with where/how to best mount the display for six months.
Calibrate the instrument using the instructions but backwards: ie. you are
looking for a certain calculated number to appear, so you fuss with the
multiplier constant at a given engine RPM X your reduction ration to give
the number you are lookin for.
While you are doing this, you realize that the reason you are doing it is to
calculate a DR speed. Flash. So you fuss with the constant to have the
instrument read your DR speed directly.
BTW, now you have an instrument which aggregates total shaft miles/hours,
trip miles/hours,etc. etc.
For $30.
Now, how bad is that for a marine instrument?
Richard
PS Mine is dead accurate to the measured mile speed from about 3kn to 7.65kn
at which point it curves up from actual speed (hull length effect) at a
predictable rate.
