https://wiki.robotika.sk/robowiki/index.php?title=Measurements_of_NXT_motors&feed=atom&action=historyMeasurements of NXT motors - Revision history2024-03-29T05:33:22ZRevision history for this page on the wikiMediaWiki 1.30.0https://wiki.robotika.sk/robowiki/index.php?title=Measurements_of_NXT_motors&diff=1687&oldid=prevPalo: preklep2006-12-03T23:43:31Z<p>preklep</p>
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<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>The NXT output signals seem to be able to eliminate overshoot, and other ugly effects seen</div></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>The NXT output signals seem to be able to eliminate overshoot, and other ugly effects seen</div></td></tr>
<tr><td class='diff-marker'>−</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #ffe49c; vertical-align: top; white-space: pre-wrap;"><div>in the RCX motor plots. The RCX oscillates its motor output on 500 <del class="diffchange diffchange-inline">kHz </del>in both firmwares.</div></td><td class='diff-marker'>+</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div>in the RCX motor plots. The RCX oscillates its motor output on 500 <ins class="diffchange diffchange-inline">Hz </ins>in both firmwares.</div></td></tr>
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</table>Palohttps://wiki.robotika.sk/robowiki/index.php?title=Measurements_of_NXT_motors&diff=1674&oldid=prevPalo at 17:56, 1 December 20062006-12-01T17:56:47Z<p></p>
<p><b>New page</b></p><div>We have been curious how do actually the signals that control the NXT motors<br />
look like. The NXT output cable has 6 wires:<br />
<br />
MA0, MA1 - "PWM" output signals to actuators<br />
GND, POWERMA - optional power source for embedded devices<br />
TACHOA0, TACHOA1 - internal rotation sensors<br />
<br />
The MA0, MA1 are compatible with the RCX's motor, so they are not any<br />
kind of control signal to a servo motor, they are simply connected to<br />
two poles of a DC motor so that they can drive it forward or backward<br />
depending on changing polarity.<br />
<br />
When the motor is running full-speed, the MAX signals are simply connected<br />
to ground and battery voltage to drive the motor maximum speed. When the<br />
motor strength is decreased, the power is supplied in impulses with length<br />
proportional to the desired power:<br />
<br />
[[Image:nxt_motor_50_percent.png | NXT motor running half speed]]<br><br />
Plot of the MA signal when NXT motor is running half speed (50%).<br />
<br><br><br />
<br />
[[Image:nxt_motor_75_percent.png | NXT motor running 75% speed]]<br><br />
Plot of the MA signal when NXT motor is running 75% speed.<br><br />
(note that the drive is supplied when the signal is low; <br />
the other MA signal is always high). Similarly, the signal looks<br />
the same, just inverted for 25% power.<br />
<br />
'''So the frequency of oscillations generated by NXT is 8kHz'''.<br />
<br />
And it is possible to drive the old RCX motors using these outputs and<br />
the conversion cable supplied by LEGO.<br />
<br />
It can be interesting to compare these measurements to signals generated<br />
by RCX: we look at both the standard firmware and BrickOS firmware. Those<br />
signals look like this:<br />
<br />
[[Image:rcx_motor_rcx_motor_nqc_57_percent.png | RCX motor running on power 4 out of 7 with standard firmware (and NQC program)]]<br><br />
RCX motor running on power 4 out of 7 with standard firmware (and NQC program).<br><br />
<br><br />
<br />
[[Image:rcx_motor_rcx_motor_brickos_50_percent.png | RCX motor running on half of full power with BrickOS firmware]]<br><br />
RCX motor running on half of full power with BrickOS firmware.<br><br />
<br><br />
<br />
[[Image:rcx_motor_rcx_motor_brickos_75_percent.png | RCX motor running on 3/4th of full power with BrickOS firmware]]<br><br />
RCX motor running on 3/4th of full power with BrickOS firmware.<br><br />
<br><br />
<br />
The NXT output signals seem to be able to eliminate overshoot, and other ugly effects seen<br />
in the RCX motor plots. The RCX oscillates its motor output on 500 kHz in both firmwares.<br />
<br><br><br />
<br />
Finally, once we had an oscilloscope on, we also looked at the signal on the RCX's activated<br />
light sensor, it looks as follows (with BrickOS firmware):<br />
<br />
[[Image:rcx_light_brickos.png | RCX active light sensor sampling]]<br><br />
RCX active light sensor sampling.<br><br><br />
<br />
It appears that the sampling frequency is about 6.5 kHz.</div>Palo