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2020 Baseline [9th Jan 2020]

A project log for All Ball Drive - Adventures in Spherical Motors

Using Arduino to create a Spherical Drive System

Alex DunnettAlex Dunnett 01/09/2020 at 16:090 Comments

September 2019 - 9th Jan 2020


As this is my first log in the Hackaday context I thought I'd share where I'm up to at the start of this new decade (and approx. halfway through my project).

Research

and boy has there been a lot of this.

Dare I say that by the current stage of the project this section is complete?

Probably not, but if I have to come back up from the little research hole where I've burrowed into then it means something has gone horribly, horribly wrong.


Rigs

So far a rig has been developed in CAD. This rig will house a singular stator, a cylindrical rotor and the whole collection of Arduino, batteries and electronic circuits that go along with it. The foundations of the rig can also be used to support the spherical rig once that has been designed.

Analytical Calculations

Rough pen and paper calculations so far, but looking to generate some more concrete figures in MATLAB over the coming days. 

Electromagnetic Simulation

By using the Ansys Maxwell software provided free by my university (and after watching some number of youtube videos by a bloke called Kamyar K.) I will be able to more accurately simulate the performance of my drive system, hopefully informing my design such that the final iteration will at least turn. Even just a little bit :P

Progress here has been hampered partially by Ansys' immensely unfriendly user interface, but mostly because most of my time in the recent month or so has been spent trying to solve the problem in the next section...

Power Supply

The real crux of the problem. Once this has been solved then this whole project will become a good deal more straightforward. 

Essentially, I know that I need to generate at least two (preferably 3) phases of AC current from a DC power supply. In the previous term I attempted to do this almost solely within the context of Arduino, as I was quite inexperienced with conventional electronics and eager to learn more about programming in the process.  

To this end I combined an Arduino UNO with a few Arduino Motor-shield Rev 3.'s and developed some code to output a PWM signal that mimicked a sinusoidal AC waveform, using the motor shield's L298 H-Bridge to invert the signal every half period. This gave me control over the frequency of the signal as well as giving me the option to easily use sensor feedback to adjust the performance of the device.

Before Christmas I thought I had managed to achieve this, as indicated by the attached image. However upon trying to combine the two half signals into one or apply a low-pass filter circuit the waveforms generated did not look at all correct. (These circuits were very basic however, only featuring a sparse collection of resistors and capacitors).

So to all those who have struggled to the end of this post - 

 Anybody got any advice when it comes to generating 3 Phase AC power from an Arduino-based system for an electronics newbie? Any tips would be appreciated :D

-Also if the advice could focus on the Arduino + Motor shield Combination then that would be ideal, as I have already put a reasonably large amount of my project budget into those components. (Not the end of the world though).


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