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n2ic wrote: As far as I'm aware, the resistor is in series with the motor. Correct me if I'm wrong.

That is not correct.

Rule 2.d.iv. ..."wired in parallel with the motor/generator"...

Interestingly, you are both actually correct. I've had this debate with many people, and it's both in series and parallel. Think about it this way: there are only 2 wires coming out of the motor, and 2 wires coming out of the resistor. Neither the motor or resistor care about direction of current / voltage. As a result, there is only 1 way to hook them together to make a circuit (connect 1 motor wire to 1 resistor wire and the other wires to each other). As a result, you could make the argument either way regarding whether this is a series or parallel circuit.

n2ic wrote:
My interpretation of the 3 cm in the drawing is that no part of the blade can be within 3 cm of the axis of the CD mount hub.

I certainly hope this is correct - My scavenged CD motor uses a magnet to hold the CD in place - i.e. the student blade assembly sits between the motor and the magnet. The magnet is circular with a radius of 2.5 cm.

What say, chalker ?

Thanks !

Yep.

chalker wrote:

n2ic wrote:
My interpretation of the 3 cm in the drawing is that no part of the blade can be within 3 cm of the axis of the CD mount hub.

I certainly hope this is correct - My scavenged CD motor uses a magnet to hold the CD in place - i.e. the student blade assembly sits between the motor and the magnet. The magnet is circular with a radius of 2.5 cm.

What say, chalker ?

Thanks !

Yep.

Huh? The rules say that there is no limit on how far forward the blade assembly may extend. The 3 cm radial distance only applies to the blade being behind the mounting plane. n2ic's described motor mount would prevent the blade assembly from being within the 3 cm even in front of the mounting plane.

chalker wrote:

n2ic wrote: As far as I'm aware, the resistor is in series with the motor. Correct me if I'm wrong.

That is not correct.

Rule 2.d.iv. ..."wired in parallel with the motor/generator"...

Interestingly, you are both actually correct. I've had this debate with many people, and it's both in series and parallel. Think about it this way: there are only 2 wires coming out of the motor, and 2 wires coming out of the resistor. Neither the motor or resistor care about direction of current / voltage. As a result, there is only 1 way to hook them together to make a circuit (connect 1 motor wire to 1 resistor wire and the other wires to each other). As a result, you could make the argument either way regarding whether this is a series or parallel circuit.

A series connection would be this...One of the motor wires to the resistor. The other side of the resistor to one of the voltmeter leads. The other voltmeter lead to the other motor wire. That would give very different results.

0ddrenaline wrote:

chalker wrote:

n2ic wrote:
My interpretation of the 3 cm in the drawing is that no part of the blade can be within 3 cm of the axis of the CD mount hub.

I certainly hope this is correct - My scavenged CD motor uses a magnet to hold the CD in place - i.e. the student blade assembly sits between the motor and the magnet. The magnet is circular with a radius of 2.5 cm.

What say, chalker ?

Thanks !

Yep.

Huh? The rules say that there is no limit on how far forward the blade assembly may extend. The 3 cm radial distance only applies to the blade being behind the mounting plane. n2ic's described motor mount would prevent the blade assembly from being within the 3 cm even in front of the mounting plane.

It's not a question of how far forward the blade assembly may extend. The question is how close can the blades be to the axis of rotation of the motor.

n2ic wrote: It's not a question of how far forward the blade assembly may extend. The question is how close can the blades be to the axis of rotation of the motor.

Sorry, that was sort of irrelevant now that I think of it. However, a distinction is made between the blade being "behind" the mounting plane and the blade being "forward." The 3 cm radius rule is only stated to apply to the blade being behind the mounting plane.

I am confused also. To expand on what 0ddrenaline is asking - The rules state "no part of the blade assembly may extend BEHIND the mounting plane of the CD for a radial distance of 3 cm." They go on to clarify the reason for this is to "ensure clearance with the motor/generator support stand." There is a clarifying picture right after that rule showing the "front view" with blades going all the way to the center of the CD.

Is the presence of resistors for the sole purpose of not giving erratic readings? Or does it require a change in the design of the blades (as in 2011) , as opposed to a test bench without resistors at all?

The resistors are load. You shouldn't have to change your blade design, this has more to do with the power generated than how it's generated.

So to clarify, the resistors are just there so we can calculate power, then? My testing device doesn't show a decrease in RPM when resistors are attached....so there doesn't seem to be a braking effect with the load.