A blog about mechatronics

So I wrote applications for a competition for bachelors thesises at Chalmers University of Technology, called Bachelors Challenge.  After passing two steps of selection, we got to present our concept in front of a public audience and a jury consisting of representants from Chalmers and various companies, including the internationally famous Ångpanneföreningen. We competed in the category "Green Initiative and Sustainable Development". Madeleine, another person from our six person team and I held the presentation. Competition was hard. One of the competitors for instance presented a concept for converting plant matter that is wasted today into useful plastics. To our help Jens and Madeleine, from our  group consisting of six persons, built a model of the windturbine. As we couldn't find a suitable source of wind we decided to spin the turbine with a DC motor instead. Then we used my previously designed software to make an onscreen live demonstration of the performanc...

The first practical tests have commenced! The windmill below is built within this Bachelors Thesis:  We had worked in small subgroups, where I had focused on calculations, software and electronics. Some other guys had done the mechanical design and therefore I didnt't see the turbine first until the day all parts were to be assembled. What I hadn't realised before is that the turbine is huge! It measures some above 3 meter in height. Here is a rather crappy first movie of over first test run:  Turbine control is done via electronic switching by using PWM. A Maximum Power Point tracking algorithm is tried here. Among other things wind and electrical output (voltage and current) are measured that can be used to evaluate system performance. This can be used for estimating turbine output. The current measurement was bit of a challenge to design as it had to work over the unusually large range 0,5- 60 amps. The measurement is split up in to ranges in hardwa...

Since the last post a lot of effort has been dedicated to a presentation and mid-project report so little concrete work has been done in the project itself. Today I however played around with some equations and got a new one of interest. I haven't double checked it yet though so full disclaimer. However, it seems that the steady state conduction losses in relation to it's produced shaft power in a DC machine connected to a Savonius turbine with a radius r can be expressed as \$ P_{cond.loss,frac}=\frac{P_{cond.loss}}{P_{shaft}} = \frac{R \rho H V C_{p0}}{\lambda_0 k n}r^3 \$ (1) where V is the wind speed,  R is the DC machine series resistance, Roh is the air density  H is the rotor height, Cp0 denotes the turbine effiency and lambda a desired tip-to-wind-speed-ratio, both assumed to be constant (a good approximation if a controller is used). Furthermore  k is the ideal DC machine constant and n is a gearing ratio between the turbine and DC machine shaft assum...

There were some issues during the first tests due to that the output voltage from the generator was too low. The generator voltage can be raised by using a gearing factor n that increases the rotational speed and therefore the EMF voltage by  EMF = n*k*w where k is the motors voltage constant and w is the wind turbine's rotational speed. The generator will spin faster and therefore generate more voltage, simply put.  When a gearing is introduced the torque on the generator's rotor is also decreased. This reduces the copper losses  Ploss,copper = r*I^2 ~ r*(T/(k*n))^2  as the current I is directly proportional to the torque T, and inversely proportional to a theoretical motor constant k, in theory. Lower rotor torque thus means that the copper losses are reduced.  Reluctance effects However, the BLDC motor used is affected by quite a lot of  reluctance effects. An initial torque of a certain level is needed to overcome the ...

Cut a barrel in half, mount it on a shaft and you have a windturbine. If the barrel is used, then what else probably would end up on a scrap heap is instead used for converting renewable energy. Simplicity and low cost makes this an attractive option especially for societies with limited economy and a malfunctioning or non existing electric grid. Small off-grid electrical networks can be built and people who perhaps most needs electricity get that. Isn't that neat? Savonius (from http://solarvan.co.uk/savonius) An overlooked potential? The Savonius though has a widespread reputation of having low effiency and is often dismissed as a credible option around forums and in formal litterature. However, when looking at the graph below from a publication Wortman did 1983, the effiency can be realtively high provided that the TSR(Tip-to-Wind-Speed-Ratio) is held at a correct value and the windmill should work quite nicely. In practice this could probably be done by con...

Before Stockholm Robot Championship 2013 I built a prototype for a line follower robot. The goal was to build something quickly that would be easy to modify, get it to go around the track and then learn as much as possible for a perhaps next version to come. It's the first robot I've built, apart from basic one we built in a project course.  I tried an Olimexino ARM development board for this project. It's basically an Arduino clone but it's physically smaller and lighter than the Arduino Due board, and cheaper, at least on eBay. I had slight problems with the drivers on this board. Here are some info about Olimexino drivers that at least helped me: http://forums.leaflabs.com/topic.php?id=73  However, when considering the "bang for the buck" Olimexino is still an attractive choice when compared to Arduino I think.   I have some stuff laying around in the drawer that I would like to try out on this robot if I choose to continue on it. For instance I w...

I've gotten it to start! The electronic systems had probably been doing their parts correctly for a long time. Problems were in the mechanics department of the engine, where valve clearance was missing.  That resulted in that the valves never closed correctly and compression was lost.  After fixing that, the engine once again gave signs of life just after a few kicks.  First it didn't want to rev up, so I thought that the carburetor was giving me troubles as it usually does. I tried to move the ignition trig point from around 17° to 30° before TDC (the same as opening the breaker-points on the original system). The first of the aforementioned points is marked from factory with an “F”,  17° before TDC,  and this is where the pre-ignition is supposed to begin when the motor is standing still.  Point number two is the one  30° before TDC,   also factory marked, but without text. Maybe that one marks when the spark is supposed to come when the engin...