CDK20 Focuser - Revision history

WikiSysop: /* Replacement Motors and Encoders */

2013-07-25T21:57:51Z

Replacement Motors and Encoders

← Older revision		Revision as of 21:57, 25 July 2013
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	== Replacement Motors and Encoders ==		== Replacement Motors and Encoders ==

	In the event the encoder or the motor fails, an alternative to the Celestron part is offered by [http://www.phidgets.com/products.php?category=10&product_id=3264E_0 Phidgets]. One that appears to be suitable is their model 3264E_0, a 12 V, 8.4 Kg-cm, 28 RPM, 139:1 gearmotor and encoder with a 6 mm shaft. The encoder is the same type ~~uses~~ on the Celestron motor, and the shaft will match the Hedrick focuser shaft extension and adapter to the bevel gear. The motor has good torque, but not so high that it will damage its own gears if it stalls. Its stall current is 1.5 A, within the capacity of the Phidgets controller.		In the event the encoder or the motor fails, an alternative to the Celestron part is offered by [http://www.phidgets.com/products.php?category=10&product_id=3264E_0 Phidgets]. One that appears to be suitable is their model 3264E_0, a 12 V, 8.4 Kg-cm, 28 RPM, 139:1 gearmotor and encoder with a 6 mm shaft. The encoder is the same type used on the Celestron motor, and the shaft will match the Hedrick focuser shaft extension and adapter to the bevel gear. The motor has good torque, but not so high that it will damage its own gears if it stalls. Its stall current is 1.5 A, within the capacity of the Phidgets controller.

	The encoders on the Celestron motors are interchangable. Under the plastic cover the encoder disk is held to the shaft by a set screw. If the screw is carefully loosened, the disk may be slipped off. Two screws hold the circuit board which may be removed and swapped for a replacement. We note this because we had an encoder circuit board failure on CDK20N after 6 years of service.

			The encoders on the Celestron motors are interchangable. Under the plastic cover the encoder disk is held to the shaft by a set screw. If the screw is carefully loosened, the disk may be slipped off. Two screws hold the circuit board which may be removed and swapped for a replacement. We note this because we had an encoder circuit board failure on CDK20N after 6 years of service.

	== Focuser Software ==		== Focuser Software ==

WikiSysop at 21:56, 25 July 2013

2013-07-25T21:56:54Z

← Older revision		Revision as of 21:56, 25 July 2013
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	[[File:focuser_phidgets_electronics_overview_sm.jpg\|300px\|center]]		[[File:focuser_phidgets_electronics_overview_sm.jpg\|300px\|center]]


			== Replacement Motors and Encoders ==

			In the event the encoder or the motor fails, an alternative to the Celestron part is offered by [http://www.phidgets.com/products.php?category=10&product_id=3264E_0 Phidgets]. One that appears to be suitable is their model 3264E_0, a 12 V, 8.4 Kg-cm, 28 RPM, 139:1 gearmotor and encoder with a 6 mm shaft. The encoder is the same type uses on the Celestron motor, and the shaft will match the Hedrick focuser shaft extension and adapter to the bevel gear. The motor has good torque, but not so high that it will damage its own gears if it stalls. Its stall current is 1.5 A, within the capacity of the Phidgets controller.

			The encoders on the Celestron motors are interchangable. Under the plastic cover the encoder disk is held to the shaft by a set screw. If the screw is carefully loosened, the disk may be slipped off. Two screws hold the circuit board which may be removed and swapped for a replacement. We note this because we had an encoder circuit board failure on CDK20N after 6 years of service.

WikiSysop: /* Motor and Encoder */

2013-07-25T21:46:49Z

Motor and Encoder

← Older revision		Revision as of 21:46, 25 July 2013
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	== Motor and Encoder ==		== Motor and Encoder ==

	The CDK20 focuser motor is a DC servo with an integral optical encoder. A stock Celestron CPC telescope RA or declination motor has been augmented with a machined plate to attach it to the focuser. The bevel gear, approximately 1/2 the diameter of the matching gear on the focuser, engages the focuser gear. There is a shaft extension that positions the motor gear. On the CDK20's the spacing may require shims. The motor assembly is shown below.		The CDK20 focuser motor is a DC servo with an integral optical encoder. A stock Celestron CPC telescope RA or declination motor has been augmented with a machined plate to attach it to the focuser. The bevel gear, approximately 1/2 the diameter of the matching gear on the focuser, engages the focuser gear. There is a shaft extension that positions the motor gear and matches the motor's 6 mm shaft to the gear's 0.250-inch bore. On the CDK20's the spacing may require shims.

			The motor that was provided with our telescopes is similar to one also provided with the Hedrick focuser on our CDK125. Apart of the wiring differences which are undoubtedly the result of product development, the motor on the CDK125 has a lower gear ratio and therefore lower torque than the one on the CDK20. Consequently, they are not interchangable because our CDK20's will stall with the low torque motor. It appears that the high torque version is no longer offered as a standard Celestron replacement part.

			The motor assembly is shown below.

WikiSysop at 20:18, 14 July 2013

2013-07-14T20:18:15Z

← Older revision		Revision as of 20:18, 14 July 2013
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	[[File:focuser_phidgets_electronics_overview_sm.jpg\|300px\|center]]		[[File:focuser_phidgets_electronics_overview_sm.jpg\|300px\|center]]



			== Focuser Software ==


			[http://www.astro.louisville.edu/software/pyfocus/index.html PyFocus] is a Python-based set of programs to control the focuser. It is all-in-one standalone code that is scriptable, and also configured to work with [http://www.astro.louisville.edu/software/xmtel/index.html XmTel] and [http://www.astro.louisville.edu/software/xmccd/index.html XmCCD] for telescope control and image acquisition. Although the code is designed to enable setting the focus based on the measured image defocus for a Planewave CDK20, these parameters are easily modified. It may also be adapted to controlling any small encoded DC motor using the Phidgets hardware.

WikiSysop: /* Servo Controller Wiring and Enclosure */

2013-07-14T20:10:46Z

Servo Controller Wiring and Enclosure

← Older revision		Revision as of 20:10, 14 July 2013
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	The motor with the Phoenix connector is shown below.		The motor with the Phoenix connector is shown below. Phoenix pin 1 in our numbering is upper right, connected to the encoders. Pin 8 on the lower left goes to the motor power.

	[[File:focuser_motor_wired_sm.jpg\|300px\|center]]		[[File:focuser_motor_wired_sm.jpg\|300px\|center]]

WikiSysop: /* Phidgets 1065 Servo Control */

2012-07-16T16:29:29Z

Phidgets 1065 Servo Control

← Older revision		Revision as of 16:29, 16 July 2012
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	The board requires 9 to 28 VDC power and returns a the PWM control power to the small motor. It keeps a total full count (not the more precise quarter wave count) of each encoder transition. An open source library accompanied by C, Java, and Python examples allows straightforward interfacing of their devices to telescope control programs.		The board requires 9 to 28 VDC power and returns a the PWM control power to the small motor. It keeps a total full count (not the more precise quarter wave count) of each encoder transition. An open source library accompanied by C, Java, and Python examples allows straightforward interfacing of their devices to telescope control programs.

	We enclose the servo control card in a separate aluminum box near the telecope focus, and provide a center off DPDT switch to enable local control of focus through the digital inputs to the Phidgets board. An RTD thermal sensors located near the primary mirror and on an OTA strut are connected to the motor control module so that our software can access the telescope temperature and the focus encoder count, in the same code that can change the focus setting at controlled speeds.		We enclose the servo control card in a separate aluminum box near the telecope focus, and provide a center off DPDT switch to enable local control of focus through the digital inputs to the Phidgets board. RTD thermal sensors located near the primary mirror and on an OTA strut are connected to the motor control module so that our software can access the telescope temperature and the focus encoder count, in the same code that can change the focus setting at controlled speeds.

	== Servo Controller Wiring and Enclosure ==		== Servo Controller Wiring and Enclosure ==

WikiSysop: /* Phidgets 1065 Servo Control */

2012-07-16T07:54:57Z

Phidgets 1065 Servo Control

← Older revision		Revision as of 07:54, 16 July 2012
Line 118:		Line 118:
	The board requires 9 to 28 VDC power and returns a the PWM control power to the small motor. It keeps a total full count (not the more precise quarter wave count) of each encoder transition. An open source library accompanied by C, Java, and Python examples allows straightforward interfacing of their devices to telescope control programs.		The board requires 9 to 28 VDC power and returns a the PWM control power to the small motor. It keeps a total full count (not the more precise quarter wave count) of each encoder transition. An open source library accompanied by C, Java, and Python examples allows straightforward interfacing of their devices to telescope control programs.

	We enclose the servo control card in a separate aluminum box near the telecope focus, and provide a center off DPDT switch to enable ~~selection of~~ local control of focus through the digital inputs to the Phidgets board. An RTD thermal sensors located near the primary mirror and on an OTA strut are connected to the motor control module so that our software can access the telescope temperature and the focus encoder count, in the same code that can change the focus setting at controlled speeds.		We enclose the servo control card in a separate aluminum box near the telecope focus, and provide a center off DPDT switch to enable local control of focus through the digital inputs to the Phidgets board. An RTD thermal sensors located near the primary mirror and on an OTA strut are connected to the motor control module so that our software can access the telescope temperature and the focus encoder count, in the same code that can change the focus setting at controlled speeds.


	== Servo Controller Wiring and Enclosure ==		== Servo Controller Wiring and Enclosure ==

WikiSysop: /* Motor and Encoder */

2012-07-16T07:50:28Z

Motor and Encoder

← Older revision		Revision as of 07:50, 16 July 2012
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	[[File:hedrick_focuser_encoder_02_sm.jpg\|600px\|center]]		[[File:hedrick_focuser_encoder_02_sm.jpg\|600px\|center]]


	Based on the E4P datasheet, the pins are		Based on the E4P datasheet, the pins are

WikiSysop: /* Servo Controller Wiring and Enclosure */

2012-07-16T07:49:11Z

Servo Controller Wiring and Enclosure

← Older revision		Revision as of 07:49, 16 July 2012
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	The completed enclosure is shown before installation on the telescope.		The completed enclosure is shown before installation on the telescope.

	[[File:~~focuser_control_enclousure_sm~~.jpg\|300px\|center]]		[[File:focuser_control_enclosure_sm.jpg\|300px\|center]]

WikiSysop: /* Servo Controller Wiring and Enclosure */

2012-07-16T07:48:14Z

Servo Controller Wiring and Enclosure

← Older revision		Revision as of 07:48, 16 July 2012
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	[[File:Phidgets_servo_encoder_cable.jpg\|300px\|center]]		[[File:Phidgets_servo_encoder_cable.jpg\|300px\|center]]


			The motor with the Phoenix connector is shown below.

			[[File:focuser_motor_wired_sm.jpg\|300px\|center]]


			The cable connects to the Phidgets card shown in its housing.

			[[File:focuser_phidgets_board_wired_sm.jpg\|300px\|center]]


			The completed enclosure is shown before installation on the telescope.

			[[File:focuser_control_enclousure_sm.jpg\|300px\|center]]


			This overview shows the focuser motor with its wiring harness, two temperature sensors, and the control module.

			[[File:focuser_phidgets_electronics_overview_sm.jpg\|300px\|center]]