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<DIV style="FONT: 10pt arial">----- Original Message -----
<DIV style="BACKGROUND: #e4e4e4; font-color: black"><B>From:</B> <A
title=admin@datta.vic.edu.au href="mailto:admin@datta.vic.edu.au">Judy Moore</A>
</DIV>
<DIV><B>To:</B> <A title=eo@datta.vic.edu.au
href="mailto:eo@datta.vic.edu.au">Adriana Agosta</A> </DIV>
<DIV><B>Sent:</B> Friday, September 14, 2007 9:50 AM</DIV>
<DIV><B>Subject:</B> Fw: Gear ratio formula</DIV></DIV>
<DIV><BR></DIV>
<DIV> </DIV>
<DIV style="FONT: 10pt arial">----- Original Message -----
<DIV style="BACKGROUND: #e4e4e4; font-color: black"><B>From:</B> <A
title=barton.paul.s@edumail.vic.gov.au
href="mailto:barton.paul.s@edumail.vic.gov.au">Barton, Paul S</A> </DIV>
<DIV><B>To:</B> <A title=admin@datta.vic.edu.au
href="mailto:admin@datta.vic.edu.au">admin@datta.vic.edu.au</A> </DIV>
<DIV><B>Sent:</B> Wednesday, September 12, 2007 8:29 PM</DIV>
<DIV><B>Subject:</B> Gear ratio formula</DIV></DIV>
<DIV><BR></DIV>
<DIV><FONT color=#000000 size=1>I have been working with Lorraine Tran and
Kristin Allen from the VCAA in trying to resolve the issues with the gear ratio
formula that was used in the 2006 exam in question 4h and 4i. In the 2006
assessment report the formula used was driver over driven for both questions.
This resulted in the wrong gear ratio for 4h answer given 5:1, should be 1:5.
For every one turn of the driver (60 tooth) : 5 turns of the driven (12
tooth), or large gear drives a small gear faster. The correct formula is
<STRONG>driven over driver</STRONG>. This is obvious in the answer given in 4i.
The incorrect answer was that a 4,800 toothed gear be fitted to a 1200RPM
electric motor as the driver and then meshed with a 12 toothed driven gear to
produce a 3 RPM output speed. Ignoring the practicalities of trying to create
this scenario in reality, this is embarrassing that due to this incorrect
formula being used the larger gear is calculated to be placed onto the shaft of
the electric motor. To stay with the scenario the small gear has to be fitted to
the electric motor and the larger gear to the output shaft.</FONT></DIV>
<DIV><FONT size=1>Kristin Allen has pointed out to me that she must follow the
2007 Study Design in which on page 37 it states:</FONT></DIV>
<DIV>
<P class=MsoNormal
style="MARGIN: 0cm 0cm 0pt; mso-layout-grid-align: none"><SPAN lang=EN-US
style="FONT-SIZE: 8.5pt; COLOR: #20231e; FONT-FAMILY: HelveticaNeue-Roman; mso-ansi-language: EN-US">Gear
ratio<SPAN
style="mso-spacerun: yes">
</SPAN>A mathematical representation of the ratio of gear teeth in gear trains
(e.g. 60<o:p></o:p></SPAN></P>
<P class=MsoNormal
style="MARGIN: 0cm 0cm 0pt; mso-layout-grid-align: none"><SPAN lang=EN-US
style="FONT-SIZE: 8.5pt; COLOR: #20231e; FONT-FAMILY: HelveticaNeue-Roman; mso-ansi-language: EN-US">teeth
gear drives 30 teeth gear, 60:30 or 2:1). </SPAN><U><SPAN lang=EN-US
style="FONT-SIZE: 8.5pt; COLOR: #3366ff; FONT-FAMILY: HelveticaNeue-Roman; mso-ansi-language: EN-US">(driver
over driven). </SPAN></U></P>
<P class=MsoNormal
style="MARGIN: 0cm 0cm 0pt; mso-layout-grid-align: none"><SPAN lang=EN-US
style="FONT-SIZE: 8.5pt; COLOR: #3366ff; FONT-FAMILY: HelveticaNeue-Roman; mso-ansi-language: EN-US"><FONT
color=#000000 size=1>This is incorrect, 2 turns of the 60 gear does not result
in 1 of the driven and if the output speed= input speed/ VR, the wrong speed
would be calculated. The correct formula is DRIVEN / DRIVER. Lorraine Tran asked
why no one has raised this before but I've heard lots of people raise this at
the TEAV systems study design units 1&3.</FONT></SPAN></P>
<P class=MsoNormal
style="MARGIN: 0cm 0cm 0pt; mso-layout-grid-align: none"><SPAN lang=EN-US
style="FONT-SIZE: 8.5pt; COLOR: #3366ff; FONT-FAMILY: HelveticaNeue-Roman; mso-ansi-language: EN-US"><FONT
color=#000000 size=1>Please return your opinions quickly as our students will be
sitting this exam very soon.</FONT></SPAN></P>
<P class=MsoNormal
style="MARGIN: 0cm 0cm 0pt; mso-layout-grid-align: none"><SPAN lang=EN-US
style="FONT-SIZE: 8.5pt; COLOR: #3366ff; FONT-FAMILY: HelveticaNeue-Roman; mso-ansi-language: EN-US"><FONT
color=#000000 size=1>Thank you,</FONT></SPAN></P>
<P class=MsoNormal
style="MARGIN: 0cm 0cm 0pt; mso-layout-grid-align: none"><SPAN lang=EN-US
style="FONT-SIZE: 8.5pt; COLOR: #3366ff; FONT-FAMILY: HelveticaNeue-Roman; mso-ansi-language: EN-US"><FONT
color=#000000 size=1>Paul Barton, Systems Engineering teacher, Dromana Secondary
College.</FONT></SPAN></P></DIV>
<P></P>
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