Configuring a Motor Controller

 

Each of the motor control subsections of the motor controller are identical. As such, one may substitute one for another for testing purposes.

For these examples, a single section of the board is used, so it won't look exactly like the full triple board in the main control box. However it will suffice for the purpose of illustration.

Ribbon cable connection Board address jumpers External Control Enable Jumper Kill Switch Address Jumper Motor 1 Current Control Motor 2 Current Control Motor Connector 1 Motor Connector 2 Microstepping Jumpers for Motor 1 Microstepping Jumpers for Motor 2

 

Ribbon Cable Connection

Note that this specific board has a horizontally mounted ribbon cable connector (the 20 pin connector to the right of the board address jumpers). On the boards in production, only the filter wheel controller has this horizontal arrangement. The others have vertical pins coming straight off the board.

Unfortunately, when using the vertical mounting arrangements, the ribbon cable connector is too close to jumper 3, the "external control enable" jumper, so this jumper is mounted on the BACK of the board. As such, the board must be unmounted from the case in order to access the jumper.

Board Address

The three jumpers, numbered 0, 1 and 2, specify the board's address. This allows the main controller to send commands to a single motor control board subsection. For example, the filter wheel/ND wheel controller or the Objective/Condenser controller.

The predefined board addresses are (0 = jumper not installed. 1 = jumper installed):

000 - Filter wheel/ND wheel
100 - Objective/Condenser
010 - Polarizer/Compensator

With three 'bits', these jumpers allow selection of up to 8 different boards so the Super uController can theoretically drive 16 motors.

External Control Enable

In order to drive the motor very smoothly for an optimal interactive feel, one can connect an optical encoder based controller directly to the motor controller. This bypasses the master controller and the overhead involved with passing movement commands over the bus.

Installing this jumper enables this feature for the left motor of a given motor pair. For example, in the above board, the objective would be controlled by the optical encoder.

The optical encoder connects to the 8-pin motor connector, pins 5 and 6. These are normally used by a home sensor and a low-limit switch. Therefore, the optical encoder input is mutually exclusive with use of home sensors or low-limit switches.

Kill Switch Address

Some motors are connected to particularly sensitive components such as the objective focuser. For these items, it is often desirable to have an external control that will disable the motor - immediately halting all movement. This jumper enables the master controller to control a motor controller in this manner.

Please note that there are four addresses available. Only one jumper should be installed at a time on a given board subsection. Typically this jumper is left off of components like filter wheels or the polarizer/compensator as no harm will be done if these items move more than expected.

Note: if desired, one could wire the connections of this jumper to an external kill switch. This would provide a guaranteed motor override in the case of an electrical failure.

Motor Current Control

This potentiometer allows full control of the average current flowing to the motor windings over a range of zero to 750 ma. The motor driver circuit supports this through a chopper circuit which quickly turns the power on and off to the motor windings. This allows a very important functionality - driving the windings with high voltage. By overdriving the motor, for example running a 4 volt motor with a 12 volt supply, the magnetism in the windings builds up more quickly. Once the current reaches the desired level, the chopper turns the power off so as to maintain the current level. This allows much faster motor movement than would be possible using a lower voltage supply.

Motor Connectors

The motor connectors provide output to the motor windings as well as take inputs. Note that pin 1 is designated as the upper right pin on the connector in this picture. Pin 2 is directly below it. Pin three is just to the left of pin 1. See Cable Details for a diagram.

Pin 7 - High limit* Pin 5 - Home sensor or encoder phase A Pin 3 - Winding 2A Pin 1 - Winding 1A
Pin 8 - Ground Pin 6 - Low limit* or encoder phase B Pin 4 - Winding 2B Pin 2 - Winding 1B

* Note - the limit switches are not supported in this version of the firmware.

To change the direction of the motor, simply switch the connections to motor winding 1 by swapping the connections to pin 1 and pin 2. See Cable Details for a instructions.

Microstepping Jumpers

The microstepping jumpers allow selection of the amount of microstepping enabled for the given motor. By default, with no jumpers installed, the board provides 1/8 step microstepping. By installing one or two jumpers, one may select coarser stepping for a given motor. Typically this is not done except where the motor provides such fine steps for a device that it would take an inordinate number of steps to carry out a desired move.

Troubleshooting

Step 0: check the control panel

The very first step to take is to see what happens when you adjust the knob that should move the motor. Does the control panel LED display update properly? For example, when you rotate a focus knob clockwise, the values should increase. Rotating it counter-clockwise should make the values decrease. Likewise, the filter wheel knob should cause the LED to run from 1 to 6 when rotated clockwise.

Step 1: try a known working device

Should you have a problem with one of the motors, the first thing to try is running a known working motor on the given port. For example, if the objective is not working, try plugging in the neutral density filter wheel to see if that spins correctly. This will show you if the motor and its cabling are ok or if the problem lies deeper in the system.

Step 2: switch the internal cables

The second step to take is to try swapping the 8-pin connector from one motor known to be working to the motor that is not working. For example, in the above picture, you would put the objective on the condenser connector and the condenser cable on the objective connector. This will test the cable from the board to the front of the cabinet.

Step 3: Swap motor controllers

Make sure to turn off the power before trying this test.

If the above two test show that the motor controller itself is misbehaving, then you can try configuring one of the other motor controllers so that it thinks it is the defective controller. This is done as follows:

  1. change the address jumpers so that the working controller has the same configuration as the defective controller.
  2. move the motor connector from the defective controller to the working controller.
  3. Detach the ribbon cable from the defective controller

Turn the power back on and see if the motor works properly. Note that the objective controller uses the external control enable (see above picture) jumper installed. For testing, you do not need to worry about this jumper. However, keep in mind that the fine focus knob will not function unless this jumper is installed.

If swapping the motor controllers does not fix the problem, and the other motors still work properly, and the control panel is working properly, then there may be an intermittent connection somewhere. For example, the 8-pin connector soldered to the motor controller board may be poorly soldered. Or the cable connection could work sometimes and not others. However switching control boards should generally control for such problems.

 

Links:

Cable Details    Upgrading the Internal Software    Release Notes

Inside the main control unit    Configuring a Motor Controller

Troubleshooting Bad Switches     More Pictures

ETC Creations Main Page