minEngine | miniEngine

Hello everyone,

the new version is out and we are now in the Beta state. Here are the changes:

Added the external trigger input system for starting, stopping and shooting the camera. This will be extended in the future with additional triggers.
Added a Dashboard that is displayed when the miniEngine is running. This will make it clearer to recognize if the system is running or not.
Added a messaging system. This allows messages to the user so that the system can tell what it is actually doing.
Added a new system font. Now there are 3 choices for the ones that want to tweak their user interface for optimal readability.

The biggest and most versatile new feature is the trigger system. This allows the execution of core commands with external signals. Right now there are 3 functions implemented:

Start the engine
Stop the engine
Trigger the camera

This means that you can now start multiple miniEngines simultaneously with one signal. You can also start / stop the miniEngine or trigger the camera on certain events which could come from anywhere (‘want to play with a light sensor?). This is the current menu for the trigger setup:

The easies way to implement this new feature is this:

Please keep in mind that the trigger inputs are directly connected to the Arduino processor! This means you need to keep your signals between 0V and 3.3V – otherwise you might destroy your Arduino! If you use the above circuit and the trigger type “Falling”, it works without any external voltages and just a simple switch. In this case you can ignore the red text above.

Triggers are only active if the miniEngine was started by pressing the “Start” key. when you defined a “Start” trigger, the system will wait until it actually starts until the trigger signal arrived.

The next big new thing is the Dashboard. This is what you now see when the engine is running:

Here is the new font…

…and here the new message system in action:

I hope you like the new features and also that they allow more versatile setups and thus to boost your creativity.

Have fun and post some of your thoughts in the forum!
Airic

Here is a little manual describing how to find the correct motor calibration value for your setup – the mathematical and most precise way. This can now also be found in the documentation:

The miniEngine 2 offers the possibility to calibrate the motors you are using. This calibration takes the motor and its specifications itself as well as the rig it is driving into account. This chapter is aiming at helping you finding the correct calibration value for your motor(s). The calibration values needed, should be given with the following units:

• steps per centimeter for linear movements
• steps per degree for radial movements

As stepper motors come in a variety of form factors and specifications we need to add the most important of these specs to our calibrations. This is the degrees been moved by one full motor step. The most common one is 1.8°. This means that such a motor needs 200 full steps to do one full revelation:

$\frac{360^{\circ}}{1.8^{\circ}} = 200$

Because we are using multi-stepping to achieve a finer resolution, we need to multiply this full-step-value with the amount of sub-steps done. In this example we are using 1/16th stepping (which is the default for the recommended Big Easydriver):

$200{\times}16 = 3200$

..or if you prefer the full version

$\frac{200}{(\frac{1}{16})} = 3200$

Ok – so we need 3200 steps to do a full revelation with the stepper motor in micro- stepping-mode. Now let‘s add the rig that this motor is driving to the calculation. For now we are assuming we are driving a toothed belt with the stepper. The gearwheel has a circumference of 3.5cm. This means that 1 stepper revelation moves the belt 3.5cm. Here is how we get how much steps are needed for 1cm – which is also our final calibration value:

$\frac{1cm}{3.5cm}\times{3200}=914.29$

Now we can enter 914.29 steps / cm as the calibration value into the system.

If we had a motor that would do a radial move, the calibration-calculation would just differ in the last step. Assuming you are not using the motor to rotate your axis 1:1 but with a reduction of 1:4 (four revelations of the motor rotate the axis one time) , the final calculation-step would look like this:

$4\times\frac{3200}{360}=35.56$

The final calibration value for the radial setup is 35.56 steps / degree.

I hope someone finds this useful.

Have fun!
Airic

miniEngine

An open-source, Arduino based intervalometer and multi-axis motion-control system for time-lapse and video photography.

Tag Archives: minEngine

Update to version 2.0.4 beta

Motor calibration

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