Sunday, February 24, 2013

Experiment 10.8

In this experiment which is a virtual repeat of 10.4, we are analyzing the state of the system at 7 milli-second intervals, looking for the instantaneous current, voltage, torque, power and energy values.

Below are the thin slices of the experiment video and their corresponding current and therefore torque graphs.

Segment 1 / Expt 10.8

Segment 2 /Expt 10.8

Segment 3/Expt 10.8
1. The current graph of the wheel subassembly with the black tape is represented by the orange graph and the corresponding position of its assymetric weight (i.e. the black motor powering the wheel itself) is represented by the blue square. For convenience, I have only plotted the position of the black motor when its only in 3 orientations - up, horizontal or down. 

So take the graph for segment 1 of the video for instance. You will observe that at time index 0.4, there is a blue square up at the top. That means at time index 0.4, the black motor that drives the wheel with the black tape was pointing upward. You will also note that time index 0.4, the orange curve reads ~0.25 Amperes. That means at the time the subassembly motor was pulling 025 Amperes from the power supply.

You will also note that at the same time index, the other wheel subassembly (the one with the redtape) is also  in roughly the same position. You can tell this from the segment 1 graph, because at time index 0.4, the green triangle representing the position of the redtaped wheel subassembly is at the top, and the yellow line representing its current consumption is around 0.4 Amperes.

When the blue square and/or the green triangle are in the bottom position (on the X-axis), it means the corresponding assymetric weight of that subassembly is pointing downward.  When the are in the middle, they are pointing horizontally.

2. Further, in the graph of segment three, you see brown dots at the top of the graph, that indicates that at those time periods, the entire frame was experiencing pivoting or lifting about one of its edges.

In this fashion we are able to understand the inner dynamics of the behavior exhibited by the machine.

Noteworthy Trends:

A) Of the many very interesting things shown by the graphs, perhaps the most interesting is that during segment 3, it seems the wheel subassemblies experience gravitation opposite to what the previous segments experience.

We can deduce this because we can see from the segment 1 and segment 2 graphs that the subassembly motors draw the most current when they are lifting the assymetric weight of the black motors driving the wheels (we'll call them wheel-motors from now on) against gravity, and ponting them up. Correspondingly, it seems that the subassembly motors draw little or no current, when that assymetric weight of the wheel-motors falls in gravity from the top to the bottom, aiding the rotation of the subassembly.

You will note, however, that in the graph for Segment 3, the situation is reversed! The subassemblies draw little or no current when the wheel-motors are being lifted to the top. Further, when the subassembly is falling, the subassembly motors seems to need a lot of current to make the wheel-motors 'fall'.

Could it be that in the active phase, 'up' is 'down' and 'down' is 'up' from the perspective of the spinning wheels?

B) You will note that in the beginning of Segment 2, when the power is switched on, the wheels fight against each other (both drawing high current) till they find a way to orient their spins away from each other. Thereon, they are happy to maintain a constant rotation and draw low currents, keeping their spins opposed to each other, minimizing the net spin exhibited by the machine as a whole. (Following the path of least action it seems - it would rather the wheel- subassemblies spin internal to the machine than the entire machine roll around.)  This seems to be a property of the spin, as physically there is no reason they couldn't rotate in phase. Segment 1 in fact shows very ably that we can physically rotate them in phase when there is no significant spin momentum.

C) During Segment 3, the rules are changed again! The wheels are no longer content to be pointing in opposite directions. Now they want to be at 90 degrees to each other!

And you will notice that the most 'lift' is obtained when they are holding that 90 degree configuration for longer - and the corresponding current graphs keep at high values (indicating high torque and high power consumption).

D) Finally, you will also note that in Segment 1, the currents average no more than 0.4 Amperes while  in Segment 2, the current drawn has gone up to about 1-2 Amperes, only because we have added a single additional parameter - spin of the wheels.

Further, by the time we get to Segment 3, the currents drawn by the wheel subassemblies have spiked to 5 Amperes simply because we chose to rotate the cage as well.

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