First experiments with HB2 PMOD - Revision history

Palo: explanation

2006-12-06T05:26:19Z

explanation

Palo at 22:26, 4 December 2006

2006-12-04T22:26:20Z

Palo: ample capacitance

2006-12-04T22:23:25Z

ample capacitance

Palo: same experiment with lower frequency

2006-12-04T22:17:12Z

same experiment with lower frequency

Palo: Measurements of HB2 first experiment

2006-12-04T13:03:33Z

Measurements of HB2 first experiment

New page

We have connected the OC1B output (SERVO1 on Cerebot)
to DIR1 on [http://www.digilentinc.com/Data/Products/PMOD-HB2/HB2.pdf HB2 PMOD]
(see also [http://www.digilentinc.com/Data/Products/PMOD-HB2/HB2-brochure.pdf Brochure]
and [http://www.digilentinc.com/Data/Products/PMOD-HB2/PMOD-HB2-rm.pdf Reference manual],
and ICP1 (SERVO2 on Cerebot) to EN1 on HB2 PMOD. Then we made a program that generates
an 8 kHz signal with 50% duty cycle on ICP1, while keepng OC1B on, with the hope this
is going to steer the motor with 50% power. The NXT LEGO brick steers the motor
[[Measurements of NXT motors|in this way]]. The signal we generated looked like this:

[[Image:hb2_pmod_signal.gif]]

However, the output from the HB2 PMOD when connected to the NXT motor looked like this:

[[Image:hb2_pmod_nxt.gif]]

And when connected to the 9V LEGO Motor coming with RCX, it looked like this:

[[Image:hb2_pmod_rcx.gif]]

As a result, the NXT motor was beeping at perhaps 8 kHz, but moving very weakly,
and the 'RCX motor' was moving on kind of half speed, but with a little bit unusual sound.

The HB2 PMOD is configured to use the VCC voltage for powering motors,
which is the 9V from a DC adapter that is able to supply 2A on 9V.

All feedback will be appreciated.

Palo (ppetrovic[[Image:zavinac.gif]]acm.org).

← Older revision		Revision as of 05:26, 6 December 2006
Line 51:		Line 51:

	Citing the HB2 PMOD document: "The HB2 has ample capacitance to minimize voltage drop when motor phases are switched on." Does that have anything to do with this?		Citing the HB2 PMOD document: "The HB2 has ample capacitance to minimize voltage drop when motor phases are switched on." Does that have anything to do with this?
		+
		+	----
		+
		+	So we concluded that everything is actually fine. The difference is that NXT brick can generate a more pretty
		+	signal on the motor because it uses a different driver that connects the pin to the ground when the signal
		+	is on low, whereas HB2 probably just disconnects it. Never mind, the important point is that HB2 provides
		+	power only during the duty cycle as requested by its input. However, due to this motor feedback, lower frequencies
		+	tend to work better. We are therefore using the frequency of about 500 Hz.

	Palo (ppetrovic[[Image:zavinac.gif]]acm.org).		Palo (ppetrovic[[Image:zavinac.gif]]acm.org).

@@ Line 49: / Line 49: @@
 I have tried changing the HB2 PMOD part for a different, but they behave exactly the same.
 Could that be that the HB2 PMOD is supposed to be used in a different way?
 Palo (ppetrovic[[Image:zavinac.gif]]acm.org).

← Older revision		Revision as of 22:17, 4 December 2006
Line 25:		Line 25:

	All feedback will be appreciated.		All feedback will be appreciated.
		+
		+	----
		+
		+	Richard suggests to decrease the frequency of the signal,
		+	perhaps the frequency being too high for this setup so that the motors have time to react (?).
		+
		+	So I tested this with different frequences - 4 kHz, 2 kHz, etc. down to ca. 244 Hz. The observation is that the lower the frequency, the stronger the motor power. And the output signal from
		+	HB2 PMOD when applied to NXT motor looks as follows:
		+
		+	[[Image:hb2_nxt_motor_243Hz.gif]]
		+
		+	The observation shows that the driver manages to keep the signal low only for a relative short
		+	time, after that the signal is overridden by the currents generated by the motor... (?)
		+	See the detail of the same plot:
		+
		+	[[Image:hb2_nxt_motor_243Hz_detail.gif]]
		+
		+	Thus the actual duty cycle unintentionally increases with decreasing the frequency of the signal.
		+	The same signal applied to the old 9V LEGO motor (from RCX's set) looks as follows:
		+
		+	[[Image:hb2_rcx_motor_243Hz.gif]]
		+
		+	I have tried changing the HB2 PMOD part for a different, but they behave exactly the same.
		+	Could that be that the HB2 PMOD is supposed to be used in a different way?

	Palo (ppetrovic[[Image:zavinac.gif]]acm.org).		Palo (ppetrovic[[Image:zavinac.gif]]acm.org).

@@ Line 2: / Line 2: @@
 to DIR1 on [http://www.digilentinc.com/Data/Products/PMOD-HB2/HB2.pdf HB2 PMOD]
 (see also [http://www.digilentinc.com/Data/Products/PMOD-HB2/HB2-brochure.pdf Brochure]
-and [http://www.digilentinc.com/Data/Products/PMOD-HB2/PMOD-HB2-rm.pdf Reference manual],
+and [http://www.digilentinc.com/Data/Products/PMOD-HB2/PMOD-HB2-rm.pdf Reference manual]) ,
 and ICP1 (SERVO2 on Cerebot) to EN1 on HB2 PMOD. Then we made a program that generates
 an 8 kHz signal with 50% duty cycle on ICP1, while keepng OC1B on, with the hope this