Adding a magnetic encoder to a GM3 Gearmotor - Revision history

LIMS at 21:29, 2 January 2008

2008-01-02T21:29:36Z

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	Pull all four gears out		Pull all four gears out


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	[[Image:~~gm3-06~~.jpg\|right]]		[[Image:scuff2.jpg\|right]]


	Use 92% alcohol to wipe the grease off the crown gear, the one that turns fastest.		Use 92% alcohol to wipe the grease off the crown gear, the one that turns fastest.

			Scuff up the plastic with sandpaper.


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			[[Image:gm3-06.jpg\|right]]


	Use superglue to adhere a ring magnet to the back (flat) surface. I found it best to place the magnet, add drops of glue on the outside perimeter, and wick away excess glue with the edge of a paper tissue.		Use superglue to adhere a ring magnet to the back (flat) surface. I found it best to place the magnet, add drops of glue on the outside perimeter, and wick away excess glue with the edge of a paper tissue.

LIMS at 20:46, 27 December 2007

2007-12-27T20:46:28Z

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	* We could send the two pulse trains from the LS7183 to an up-down binary counter. An up-down ~~conuter~~ has one input that increments the count on a rising or falling edge, and another input that decrements. See the LS7183 datasheet, for examples.		* We could send the two pulse trains from the LS7183 to an up-down binary counter. An up-down counter has one input that increments the count on a rising or falling edge, and another input that decrements. See the LS7183 datasheet, for examples.
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	* The LS7184 differs from the LS7183: instead of having pulse outputs for "count up" and "count down", it has one output for "count" and another for "up vs. down.". The latter stays high or low ~~indefinately~~ (until the direction of rotation changes), so that's a signal you can visualize with an LED.		* The LS7184 differs from the LS7183: instead of having pulse outputs for "count up" and "count down", it has one output for "count" and another for "up vs. down.". The latter stays high or low indefinitely (until the direction of rotation changes), so that's a signal you can visualize with an LED.
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Lynch at 12:44, 27 December 2007

2007-12-27T12:44:23Z

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	Solder them together and insulate at least the middle lead. I used tape. Heat shrink tubing is better, if you think of slipping it on in advance.		Solder them together and insulate at least the middle lead. I used tape. Heat shrink tubing is better, if you think of slipping it on in advance.

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	[[Image:gm3-13.jpg\|right]]		[[Image:gm3-13.jpg\|right]]

Lynch at 12:41, 27 December 2007

2007-12-27T12:41:29Z

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	Put it back together. In this photo you can see the magnet ring faintly through the gear		Put it back together. In this photo you can see the magnet ring faintly through the gear

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	[[Image:gm3-08.jpg\|right]]		[[Image:gm3-08.jpg\|right]]

Lynch at 12:40, 27 December 2007

2007-12-27T12:40:48Z

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	Remove the motor by hand, and the two screws with a small philips screwdriver.		Remove the motor by hand, and the two screws with a small philips screwdriver.

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	[[Image:gm3-15.jpg\|right]]		[[Image:gm3-15.jpg\|right]]
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	You may have to yank off the semi-round output coupler, which is only lightly glued on anyway.		You may have to yank off the semi-round output coupler, which is only lightly glued on anyway.

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	[[Image:gm3-04.jpg\|right]]		[[Image:gm3-04.jpg\|right]]
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	Pry the case apart with a thin blade		Pry the case apart with a thin blade

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	[[Image:gm3-05.jpg\|right]]		[[Image:gm3-05.jpg\|right]]
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	We have lots of these; they are from Amazing Magnets		We have lots of these; they are from Amazing Magnets

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	[[Image:gm3-07.jpg\|right]]		[[Image:gm3-07.jpg\|right]]
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	Unfortunately it has ribs molded into the case where the ring magnet will go. The first gear, when carrying the magnet, still seems to clear the ribs OK, but just barely. One could mill or dremel the ribs down, to be sure		Unfortunately it has ribs molded into the case where the ring magnet will go. The first gear, when carrying the magnet, still seems to clear the ribs OK, but just barely. One could mill or dremel the ribs down, to be sure

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	[[Image:gm3-09.jpg\|right]]		[[Image:gm3-09.jpg\|right]]
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	[[Image:gm3-10.jpg\|right]]		[[Image:gm3-10.jpg\|right]]
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	*pin 3 (yellow, purple) = open collector output		*pin 3 (yellow, purple) = open collector output

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	[[Image:gm3-11.jpg\|right]]		[[Image:gm3-11.jpg\|right]]
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	You may find that if you operate the motor from the same supply as the hall sensors, the motor generates so much electrical noise that the hall sensors will operate erratically. You can solve this with a 0.1uF capacitor across the power supply leads of the hall switch.		You may find that if you operate the motor from the same supply as the hall sensors, the motor generates so much electrical noise that the hall sensors will operate erratically. You can solve this with a 0.1uF capacitor across the power supply leads of the hall switch.

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	[[Image:gm3-18.jpg\|right]]		[[Image:gm3-18.jpg\|right]]
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	Here's an easier way to attach wires to hall switches. Shorten the leads, splay them out, tape the chips down, and tin the leads. Tin some ribbon cable too.		Here's an easier way to attach wires to hall switches. Shorten the leads, splay them out, tape the chips down, and tin the leads. Tin some ribbon cable too.

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	[[Image:gm3-14.jpg\|right]]		[[Image:gm3-14.jpg\|right]]
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	Find the best spots for quadrature signals, mark them with a pen, and then tape the hall switches to those locations with stretchy electrical tape. Tape all the way around. Superglue may not work well enough on this slippery plastic. Some strain relief for the ribbon cable is a good idea; I used the hole at the end.		Find the best spots for quadrature signals, mark them with a pen, and then tape the hall switches to those locations with stretchy electrical tape. Tape all the way around. Superglue may not work well enough on this slippery plastic. Some strain relief for the ribbon cable is a good idea; I used the hole at the end.

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	[[Image:gm3-16.jpg\|right]]		[[Image:gm3-16.jpg\|right]]
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	The other end of the ribbon cable can be attached to some 0.1" header for insertion into a solderless breadboard. (If you solder it when it's in there, however, the solderless breadboard will melt.)		The other end of the ribbon cable can be attached to some 0.1" header for insertion into a solderless breadboard. (If you solder it when it's in there, however, the solderless breadboard will melt.)

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	[[Image:gm3-12.jpg\|right]]		[[Image:gm3-12.jpg\|right]]

Lynch at 12:37, 27 December 2007

2007-12-27T12:37:41Z

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	You can also add a magnetic encoder to the Gearmotor-9, which has a 143:1 transmission ratio		You can also add a magnetic encoder to the Gearmotor-9, which has a 143:1 transmission ratio

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	[[Image:gm3-02.jpg\|right]]		[[Image:gm3-02.jpg\|right]]
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	Unclip the motor retention band using pliers		Unclip the motor retention band using pliers

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	[[Image:gm3-03.jpg\|right]]		[[Image:gm3-03.jpg\|right]]

Lynch at 12:35, 27 December 2007

2007-12-27T12:35:40Z

← Older revision		Revision as of 07:35, 27 December 2007
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	Pull all four gears out		Pull all four gears out

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	[[Image:gm3-06.jpg\|right]]		[[Image:gm3-06.jpg\|right]]


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Lynch at 12:34, 27 December 2007

2007-12-27T12:34:51Z

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Lynch at 12:34, 27 December 2007

2007-12-27T12:34:26Z

← Older revision		Revision as of 07:34, 27 December 2007
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LIMS at 16:54, 26 December 2007

2007-12-26T16:54:25Z

← Older revision		Revision as of 11:54, 26 December 2007
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	Find ~~teh~~ best spots for quadrature signals, mark them with a pen, and then tape the hall switches to those locations with stretchy electrical tape. Tape all the way around. Superglue may not work well enough on this slippery plastic. Some strain ~~releif~~ for the ribbon cable is a good idea.		Find the best spots for quadrature signals, mark them with a pen, and then tape the hall switches to those locations with stretchy electrical tape. Tape all the way around. Superglue may not work well enough on this slippery plastic. Some strain relief for the ribbon cable is a good idea; I used the hole at the end.

	[[Image:gm3-16.jpg\|right]]		[[Image:gm3-16.jpg\|right]]
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⚫	<b>Using a hall switch. </b>

	[[Image:gm3-12.jpg\|right]]		[[Image:gm3-12.jpg\|right]]


		⚫	<b>Using a hall switch. </b>

	The HAL506 and most hall switches have what is called an open-collector output. That means they can ground their output (for logic 0) but they do not source their output (for logic 1). It is as if there were a switch inside which closes, grounding the output, when a magnetic field is detected. It is the user's responsibility to use a pull-up resistor (R1) to assure that the output voltage is +5 when the switch is open.		The HAL506 and most hall switches have what is called an open-collector output. That means they can ground their output (for logic 0) but they do not source their output (for logic 1). It is as if there were a switch inside which closes, grounding the output, when a magnetic field is detected. It is the user's responsibility to use a pull-up resistor (R1) to assure that the output voltage is +5 when the switch is open.