- Last Updated: 05 June 2015
- Created: 29 April 2015
On these pages I want to introduce my DIY-motorized focuser.
I re-built the focusser from Thomas Westerhoff (http://www.astrohome.info) myself already for my Newton. This works with at least one or two limit switches and uses the driver's proven RoboFocus-ASCOM driver.
The controls are very well thought out and well designed and the functionality considerably.
As much SMD soldering and also to flash the ATMEL-microprocessors is makes it really tricky to re-build this controller.
To focus the telescope without to touch it meks me really happe and I NEED a comparable solution for my Apo.
This control should allow me to Apo to save to focus, repeatable focus positions from the computer and retrieve it.
As an option, possibly followed by a process control via pushbutton.
At a temperature compensation I can do without. Since I use my equipment exclusively mobile, the temperatures are learned to be always difficult to reproduce.
Nevertheless, an appropriate function of my recording software is provided.
The control that I use on my Newton I did not use in this case, because I want to keep all as small as possible and would like to use for this reason no limit switches.The manufacturer TRINAMIC I remembered the stepper motor controller TMCM-1110 (Step Rocker Board on www.trinamic.com).
This final control for stepper motors suitable for the following reasons just perfect for my use:
- No soldering required
- Digital inputs and outputs
- analog inputs
- Encoder input
- Reference switch input
- Seperate inputs for limit switches
- Finished interfaces and communication possibilities
- Mini-USB on board
- Of course, RS232 and RS485
- Optional CAN bus possible
One of the biggest advantages is the internal memory for scripts that allow for a stand-alone operation and, secondly, almost entirely for the communication of eg USB can take place.
This TRINAMIC own scripting language TMCL (Trinamic Motion Controll Language) is very comprehensive and is used only very limited by my application.
The main points would be the ability to be able to control the motor via ASCOM from the PC and without reference switch.
You can of course make the TMCL-LITE-Project to use and program the controller to a kind of intermediate layer, so that it directly from the example Robofocus driver can be used.
However, it takes the controller, the main advantages and to make yourself a hard time.
The elegant way would be to simply write a ASCOM driver that drives the card directly.
That reminds me it lacks the knowledge, I was forced to seek my help, which I found in Rob Morgan. One of the programmers of the ASCOM project.
The ASCOM driver is the essential element of the control focuser although he makes a very simple idea. Emphasis was put on functionality.
In the settings fixed data can be inter-sets, or you call the settings from the user variables on the TMCM-1110 board from.
There are several ways to the Board in connection with the ASCOM drivers to work:
- You put behind no data on the TMCM-1110 board and will save all parameters in the driver itself (motor current, acceleration, speed, minimum and maximum coordinate, ...) *
- You put in behind the driver board the motor parameters and call except the end positions all through the driver from *
- You lay behind more or less complex programs for referencing on the map and calls the whole parameters from only.
(Items marked with '*' has not been tested by me)
There really is not much to say about the first operation mode. Here the relevant engine parameters are completely stored in the driver.
It is necessary to specify Minimal (usually 0) and maximum position. In addition, the focuser prior to use by hand must be brought to a neutral position.
The second Operation-Mode is similar to the first. Only that parts of the parameters here are stored on the controller.
The following points are taken into account when using a script on the board:
The program starts as soon as the operating voltage is applied. Therefore applies here first to connect the motor.
In this case, the motor current should not be deposited (only) in the driver. Otherwise, it may be that this is possibly driven with a high motor current.
In the fields marked '#' in the ASCOM-Driver can be called from the Board, which were previously stored in the Bank 2. This Bank 2 on the control board holds the memory slots 0-55 for user data ready.
Only in bank 2 data can be stored. The memory banks 0 and 1 are reserved for the system. To this, I recommend the TMCL-Reference.
Here is an example for the SGP-Command (Store Global Parameter) that can be used to store some data in the Bank 2:
This command sets the value 170 is written in the memory-slot 3 of Bank 2. This can then be called by specifying #3 in the corresponding field of the driver (in my case, the motor current).
There are other ways to store data there. But more about that later.
I myself run my focuser with the third option.
It is deposited a not quite small script, which performs the following steps after the installations of the operating voltage:
First, various engine parameters are defined.
Those parameters are:
- Motor current during operation
- Motor current in standby
- ramp Mode
- Microstepping mode
written in Bank 2 and retrieved from there by the driver. After that, the focuser is moved slightly outwards to make sure that he is not at a mechanical stop. Then he goes as long inward until it abuts against a mechanical stop, which is recognized by the Stall Guard function. Now a few steps is again driven out and the position to '0'. After the motor moves as long as outward until it abuts against a mechanical stop. There is a few steps down to the inside and the value placed on space 0 in Bank 2 as the maximum value again, which I then in the driver with # 0 may retrieve. Then the focuser moves to the value '0' and is ready for use.
More detailed infromation you will find under this link.
The motor Relevant data from the driver card retrieve has the great advantage that is not necessary when using multiple focuser adjust the driver.
Recently the Version 1.1 could be released. This I present you here available for download.
Here a short List of the major changes:
- List the availible COM-Ports, and not only a list from X to Y
- a second instance off the driver can be installed for work with two independend focusers (on the guidescope and the main telescope for example)
- Download ASCOM-Driver v1.1
- Download as ZIP-archive
- StepRocker-Board at www.trinamic.com
- Trinamic Motion Controll Language