Sensible A-class physics

“Portuguese drivers in the greater Lisbon area last monday were surprised by a strange scenario: a crazy dude with a camera and tripod in the backseat of the car, going back and forth on the same road, over and over again, accelerating to 80 kph and then letting the car stop by itself. He spent a lot of time doing that, making the other occasional road users slightly unhappy (although he had spent all morning and over 100km to find a suitable road).

Fig.1 - Camera with tripod locked in back seat

When asked about it, he said he was videotaping the speedometer of the car during the experiment. He also had a number of strange wires and electrical devices on the floor of the car, which he explained were necessary to keep the camera rolling without danger of running out of battery power.”

Fig. 2 - power inverter to feed camera.

This could have been the headlines, if the police had caught me. But they didn’t. And I’ve got my data.

Status update

It’s been a long time since my last post, so some people are asking if I’m giving up or something… nope, nothing could be further from the truth.

For practical reasons, I’m working on several fronts at the same time, and this has prevented me from producing any concrete results. Let’s see…

Precise control… of what?

This is something that has been in the back of my mind for quite a while. When you step on the gas pedal, what exactly are you expecting to happen?

It’s one of those questions that is so simple, there has to be a trick in it. And in fact, there is.

Model scripts updated

I see a lot of interest these days in “Axial Flux Motors”. Not only on the web, but also here in this blog. So I’ve updated my axial flux model to run well with the rest of the framework (it was completely broken by neglect). It is still far from perfect, but at least it works.

I also took the chance to upgrade many other small aspects in all the other scripts, so be sure to download them all and try again, if you like.

More flux, please!

Njay showed me a very cool movie of a Japanese in-wheel motor built for a solar race car. It contains a feature totally uncommon in electric motors: it regulates the magnetic flux through variable geometry.

Check it out:

Fig.1 - “TIGA” Variable Air Gap Permanent Magnet Synchronous Motor of the GOGO81-WSC solar racer.
Copyright “tmise86“, Ashiya University, Japan.

It’s a very cool way to use an essential (and very old) technique called “field weakening”: the reduction of the magnetic flux in the motor. Why would anyone want to reduce the flux??…. because, if you reduce the flux at maximum speed, you also reduce the back-EMF, causing an increase in effective current and motor speed. So it’s like using an overdrive gear after the normal gearbox: you get more speed out of the motor, but less torque (because there’s actually less magnetic flux and therefore force). I tried to find a good explanation for this complex phenomenon on the web, but couldn’t… if you find any, let me know.

Anyway, this video triggered a neural response in me: I can no longer ignore the fact that I’ve been playing around with a lot less magnetic poles than the other boys who have developed in-wheel motors.

Architecture redone

After careful consideration of the usage cases and a few other deployment constraints, I remade the architectural document.

The plan now spans 4 phases, instead of 3. Just being careful.

This time I also included a sub-project breakdown. Boy, this thing really is big… so far its weight is 18 different work packages. Yummy. Work, work, work.

It is normally regarded as a “good thing” to break a complex problem down into many simple problems until the complex problem no longer poses a threat to implementation… but I think the same trade-off that usually happens in Software engineering (can you say “class explosion”?!) is also true for hardware design: you have to strike a balance between simplicity of components and the sheer total number of components… tricky.

So here is the thing again.

Comment at will.

Architectural Overview

It’s about time I put things down on paper and see what’s missing.

I’ve written a high-level requirement specification of the whole system (click for PDF).

It outlines my approach in 3 phases (Motor Development, Parallel HEV, Serial HEV) as well as the layout of the electric system for each phase.

Comments?

Source Opened

Now that my Lua scripts have grown to a respectable size, I’ve decided to publish them in an Open Source repository.

What started out as a simple script to draw a few rectangles in FEMM has grown into the start of a full-blown framework for developing electric motors… and it is still growing and changing every day.

I’ve created a SourceForge.net project for this. I haven’t spent any time with the aesthetic aspects, so there is no web page yet. However, you can access the file repository here, and it is also accessible via anonymous Subversion (SVN) access. Keep in mind that it is obviously work-in-progress.

In the future, if there is enough interest from anyone, I may give out permissions for other developers to contribute… but I don’t expect to see dozens of people rushing at the opportunity…

Halbach demystified

Now I try to understand the correct way of using the Halbach magnetic layout.

Simulation & Simulacra

Sorry for the Matrixy title, but… once a geek, always a geek.

I completed my LUA script that simulates the movement of the motor. Here’s the video.