Older blog entries for Nic (starting at number 176)

28 Jun 2006 (updated 13 Aug 2009 at 18:40 UTC) »
June 26th, 2006

So it turns out the voltage doubler circuit wasn't perfect either. When the multivibrator capacitors were small (0.1MFD) for some reason it made the output stage transistors overheat. If the 47MFD capacitors were removed, they did not overheat. I imagine the problem was caused by some sort of voltage spike from the capacitor, but it only mattered at high frequencies. This may be a problem with the new circuit also. Another problem with the old circuit was that the output voltage was actually about three volts less than twice the input voltage. I haven't tested this circuit, but the new output stage should get the voltage within a fraction of a volt of twice the input voltage.

Notice the difference in the output stages between the two circuits - I switched the position of the NPN transistor and PNP transistor. The old version was fail-safe; it was impossible for both transistors to be on at once. With this system, however, I had to choose four resistors to create a voltage divider that would ensure that only one of the transistors was on at once. If the input voltage is above 15V, the voltage divider no longer does this, and both transistors will turn on which will short negative to positive and melt the transistors. The benefit of this output stage is the much larger range in voltage.

Go to http://www.craterfish.org/teamprodigies/?pictures?2006/Jun to see the new voltage doubler circuit!

28 Jun 2006 (updated 13 Aug 2009 at 18:41 UTC) »
June 25th, 2006

I did some tests on the H-bridge circuit and made several modifications. One change was to switch the NPN power driving transistors with PNP transistors which saved a couple volts. Another change was to replace the diodes from the direction input with NPN transistors. It turned out the voltage drop accross the diodes was too much to pull the bases of the transistors low. I also made the smallest amount of resistance from negative to positive in the logic part 10 kiliohms rather than 1 kiliohm to save power, which is important when using the +24V source. It's also nice to save power wherever possible on an electric vehicle, because those miliamps add up!

Go to http://www.craterfish.org/teamprodigies/?pictures?2006/Jun to see a schematic diagram of the new H- Bridge circuit!

24 Jun 2006 (updated 13 Aug 2009 at 18:42 UTC) »
June 23rd, 2006

I did some research on the internet and discovered the solution to a high-power charge pump - the push/pull driver. This is just a combination of a PNP transistor and an NPN transistor, but it allows the output of a circuit to be shorted high or low with no resistors in between, which is what I needed. I designed and built a new circuit, and it passed my tests. I posted a circuit schematic at http://www.craterfish.org/teamprodigies/?pictures?2006/Jun.

24 Jun 2006 (updated 13 Aug 2009 at 18:42 UTC) »
June 22nd, 2006

I redesigned the H-Bridge circuit. The new design is much simpler, and hopefully won't melt any more MOSFETs. I put a circuit schematic on the progress page at http://www.craterfish.org/teamprodigies/?pictures?2006/Jun. Since that voltage doubler circuit melted too, I'll have to redesign that.. and I'm realizing that the new design will have to be capable of powering a load that draws more current than just MOSFETs - in the H-Bridge circuit I designed the 24V source has to power some of the logic circuitry also. I also realized that the current draw of the last circuit was limited by a 1k resistor, so at 24V that would be a max of 24 mA. There was also a voltage drop accross the 1k resistor whenever the circuit was powering a load, which caused some problems.

22 Jun 2006 (updated 24 Jun 2006 at 01:22 UTC) »
June 21st, 2006

I had my last finals today, and as of this afternoon at 12:00 school's out for the summer! I made my H-bridge circuit on a breadboard to test it with a small motor. I had to make some small modifications to get the circuit to work, but eventually it did. I designed the circuit to be fool-proof but about a minute after I got the circuit working.. it went up in smoke. Following the trail of melted wires, I deduced that both the left side MOSFETs had been turned on at the same time. I'm still not sure how this is possible.. maybe a component's lead touched another's. Anyway, I melted a bunch of stuff, so that's too bad. I think tomorrow I'll remake the circuit more carefully and with normal transistors.. and if it melts again I'll know the problem is with the circuit, not with an accidental short.

June 18th, 2006

I tested a charge pump circuit I designed and built yesterday. It worked great on one MOSFET, although I will have to perform additional tests, as I'm planning on using it to drive eight MOSFETs - all the high sides of the four H-bridge circuits. Yesterday I did a lot of research into H- bridge circuits and designed my own. I think I will have to make a slight modification to accomadate regenerative braking, however. I also didn't realize that I would need a charge pump or "voltage doubler" until yesterday, but once I thought about it it made sense - if I want the full 12V accross the motor and I'm using N-channel MOSFETs to drive the high end, it follows that they will need a gate voltage higher than 12V by several volts, as the gate-source voltage has to be at least 3V, and the source is already at +12V.

13 Jun 2006 (updated 13 Aug 2009 at 18:43 UTC) »
June 12th, 2006

I haven't been able to post in a while, but I have been continuing work. School's out for summer next Wednesday, so that will free up a lot of time. Today I achieved what I have been working towards for a couple weeks. I've built the left side of the front end of the electric car out of wood. It has double a-arm suspension, steering, and is driven by the 12V motor via the top-secret transmission and a u-joint driveshaft. I rebuilt a wagon to use as a rolling platform and rested the car's front end against it, as you can see in the picture on the progress page at http://www.craterfish.org/teamprodigies. I hooked up a battery and a motor controller circuit, and the motor was able to drive the platform.

27 May 2006 (updated 13 Jun 2006 at 04:09 UTC) »
May 24th, 2006

I built a small frame that held a wheel from the Xpeditor on an axle driven by my gearbox, one of the motors, and my motor controller circuit. After plugging it in to a battery, I tested the circuit and it could drive the wheel well. The wheel was in the air. The structure then fell partially apart, but as I built it between 11PM and midnight this was somewhat expected, and I was able to carry out the experiment as I intended. Soon I will build a test platform that I will actually be able to drive!

23 May 2006 (updated 13 Jun 2006 at 04:09 UTC) »
May 21st, 2006

The replacement part for the gearbox came in the mail today. I replaced the broken part and tested it out with one of the motors and it ran great! I've been doing some RentACoder.com work so when I get payed at the end of the month I'll be able to buy the parts for the other three gearboxes and build a test chassis out of 2x4's to make sure all my concepts work before spending too much on an idea that is doomed to fail.

Yesterday I went to Home Depot and bought a couple 2x4's for the test chassis, some tubing for the drivetrain, and a can of hardening foam to test another of my ideas. The idea was to use solid wheels instead of air-filled tires. The only reason I can think of to have air is to give the tire some resiliance, letting it conform to the ground and thereby provide more traction for the vehicle. As my car will be much lighter than a standard vehicle, I don't think it will need as much traction.

23 May 2006 (updated 13 Jun 2006 at 04:09 UTC) »
May 18th, 2006

The MOSFET transistors came in the mail today. I've been way too busy lately. Last night I stayed up till 4:00 A.M doing homework, and right now it's 1:00 A.M. and I'm doing homework again.

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