Paddle speed???

[Derek Warner]

on Monday, July 01, 2002 11:31 PM, Stuart Badger posted

1) If two engines are to be used then I would suggest that you ONLY use them
independently from rest. ie when turning the model about its axis at very slow
speed. At all other times use the rudder! (you may have to increase the area from
scale) and certainly if you are modelling a 'skinny' (ie a cross channel steamer with
a high beam to length ratio) on NO ACCOUNT have the paddles operating independently -
install that paddle shaft as one unit!. I would even go so far as to suggest
that unless you REALLY want to be able to 'turn on a sixpence' then fix the
shaft even on a model with a low beam to length ratio (such as a tug)

2) We have discussed paddle speed on this forum extensively. I'm now going to
put the cat amongst the pigeons and go back to my original estimate of about
60 rpm being correct (for Old Traffford) . I know this may seem terribly slow -
but don't forget that 60rpm represents 480 'pushes' a minute with a paddle wheel
having eight floats. Old Trafford's speed seems unaffected once you get over
this rotational speed (maybe due to cavitation) - but her stability is
devastated at anything over about 80rpm! and all that happens at higher
paddle speeds is that an enormous fountain of water is hurled out behind the
model whilst the paddle box vents spew water in all directions!
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>

Well - I went back to Stuart off line and asked a few other specific questions re steam
and gearing etc, but did not broach the issue of stability via differential paddle speed
or 80 RPM speed limit

If Old Trafford was built from scale plans, should not these limitations apply to all
similar sized, similar styled & similar scaled paddlers?

I borrowed a digital tachometer and confirmed my initial observation (about 1 RPM/sec)
that the 12 Vdc windscreen wiper motor at no load provides 60 RPM (or 30 RPM @ 6 Vdc)
- so I had planned to belt drive up by 3:1 (3x60) = 180 RPM which I assumed I needed,
however based upon Stuart's experience I could use a 4:1 belt drive @ 6 Vdc and end up
with 120 RPM which would allow me to use my 20 year old Futaba FP-MC5 digital speed
controller (which has a 7.2 Vdc limit)

Do any other PD's have any thoughts or comments re Stuart's posed limitations etc

regards Derek