Older blog entries for Nic (starting at number 187)

16 Aug 2006 (updated 13 Aug 2009 at 18:22 UTC) »
August 15th, 2006

I bought some wheels at Pick A Part for $80. I also ordered a MIG-100 welder kit on eBay for $140 which comes with a welding mask and wire and stuff. The welder and the angle grinder probably won't arrive for two or three weeks from now, however, so I'm gonna have to find something productive to do for the project in the meantime.

There's a picture of the wheels at http://www.craterfish.org/teamprodigies?pictures?2006/Aug - check out the nice rims!

12 Aug 2006 (updated 13 Aug 2009 at 18:23 UTC) »
August 11th, 2006

I got back from rowing 16th century style spanish longboats all day, windsurfing, and sailing at Camp Gallagher (one of my favorite places ever!), and got right back to work on the electric car. I finished an on/off circuit which I can now use rather than disconnecting all the circuitry from the batteries. It should be good for 10A to pass through it - enough to power all the electronics, including the computer. When it is off, the motor controller circuits and whatnot use about 3mA. I wanted to keep the power consumption while the vehicle is "turned off" below one milliamp, but I guess three is okay. I also went to Zeigler's Welding and bought 32 feet of 3/4" steel tubing today for $33 (not the best deal, but it saved a lot of driving) and bought a 4.5" angle grinder on eBay for $25 (comes with 5 cutting blades and 5 grinding blades.. pretty good deal!). I'm still looking for a welder I can borrow. I added up prices from receipts I have and so far I've spent somewhere over $400 on this electric vehicle.

I put some pictures up at http://www.craterfish.org/teamprodigies?pictures?2006/Aug.

30 Jul 2006 (updated 13 Aug 2009 at 18:24 UTC) »
July 29th, 2006

I made plexiglass enclosures for the three new H-bridge circuits. They are very prettiful. Pictures at http://www.craterfish.org/teamprodigies?pictures?2006/Jul.

July 28th, 2006

I got the ten MOSFETs I ordered in the mail and set out to repair the damaged H-bridge circuit. I got a good start by melting another MOSFET. I was still working on the flame- blackened board that had an unknown problem. I probably should have just started over, but I wanted first of all to find out WHAT the problem was, and second I already had most of the work done on this board.

After many hours of testing, desoldering, resoldering, and fighting combat stealth mosquitos, I found the problem. Where a 100k resistor should have been, there was a 47 ohm resistor. How frustrating. I took all my test point solders out and began resoldering components in. Just as I was soldering the last connection, the mosquitos launched a synchonized V-formation attack, but I perservered. I connected the board, and it worked. I now have all four H- bridge circuits fully functional.

Tomorrow is my last day before getting ready for camp, and my goal was to have all the electronics for the car done. I will build the plexiglass housings for the H-bridge circuits, and solder the on/off security circuit for the car, thereby completing all the circuitry.

26 Jul 2006 (updated 13 Aug 2009 at 18:26 UTC) »
July 25th, 2006

I haven't posted in a while. I just finished the emergency circuit. The signals for the H-bridge circuits (high power, low power, and direction) pass through this circuit. When the big red emergency button is pressed it will bypass the other circuitry and put the brakes on 50% to bring the car to a stop. Follow the link below to see a picture of it.

http://www.craterfish.org/teamprodigies?pictures?2006/Jul

A couple days ago I soldered the other three H-bridge circuits, but when I tested them only two worked properly. The third only ran the motor in one direction. When I got out the multimeter to test points, I accidentally touched two solder points together and the whole thing went up in flames. Not fun. I ordered some more MOSFETs, as well as four 20AH batteries which I got for under $100 including shipping and handling plus a one year warranty!

I'm leaving for a summer camp on the 31st and I'll be going up north, so I think I'll pick up Chris's welder on the way back to begin the frame.

15 Jul 2006 (updated 13 Aug 2009 at 18:33 UTC) »
July 14th, 2006

A couple days ago I made an encosure for the interface circuit. Over the past couple days I've been working on getting the reverse circuit to work, and today I soldered it and built an enclosure for it. This circuit's job is to prevent the car from being switched from drive to reverse or from reverse to drive while the car is in motion. If the reverse switch is switched to reverse while the car is driving, the green drive light turns off and the red illuminated reverse switch blinks on and off until either it is put back in the drive position or the car comes to a full stop. It works the same for going in drive from reverse. The circuit can tell if the car is moving by checking for a current accross the motor terminals. This board has 18 components per square inch and 72% of the perf holes are used.

There is a picture at http://www.craterfish.org/teamprodigies?pictures?2006/Jul

11 Jul 2006 (updated 13 Aug 2009 at 18:34 UTC) »
July 10th, 2006

I finished soldering the interface circuit today. This circuit has 12 connection wires total. It has two power wires, three wires for the gas pedal potentiometer, three wires for the brake pedal potentiometer, one wire for reverse, and three wires (direction, high-side power, and low-side power (PWM)) to control the four H-bridge circuits. These last three have indicator lights soldered onto the board - a red LED for direction, a green LED connected to the PWM signal, and a yellow LED for high-side power. I tested the circuit on the H-bridge circuit I've built with one of the motors and it worked great.

This is a complicated little circuit. When generating a PWM signal, it must ignore the gas pedal position if the brakes are on. In addition to generating the PWM signal, this circuit has to give the motor controller a direction signal. This signal must be forward if the gas pedal is down and the car is going forward and backwards if the gas pedal is down and the car is in reverse, but in both situations it must be inverted if the brakes are on. It uses an XNOR gate (or snore gate as I like to call it) to accomplish this. It also has an output to turn the high- side MOSFETs in the H-bridge circuits on or off. They are on whenever the brakes are off and off when the brakes are on.

This is definitely one of my more-compact circuits. It's smaller than the voltage doubler circuit. With a total component count of 56 and dimensions of 2 1/8" x 1 1/4", there are approximately 21 components per square inch, and that's not including wires. Of the 286 holes in the perf- board, 211 of them have a component lead or wire through them. That's 74% of the holes that are used. Look at the pictures (http://www.craterfish.org/teamprodigies?pictures?2006/Jul) to see what I mean.

6 Jul 2006 (updated 13 Aug 2009 at 18:36 UTC) »
July 6th, 2006

A few days ago I made a nice little enclosure for the voltage doubler circuit. It might even be water proof! There is a picture on July's progress page (http://www.craterfish.org/teamprodigies?pictures?2006/Jul). Yesterday I finished and printed out a circuit for all the vehicle's core electronics. Last count I think there were 75 transistors.

30 Jun 2006 (updated 13 Aug 2009 at 18:37 UTC) »
June 29th, 2006

I made an enclosure for the H-bridge circuit. It is sealed except for the two ends, so that air can flow through it to dissipate the heat. Now it's time to design the PWM generating circuit and forward/reverse/braking control circuit.

I posted a picture on the progress page for June: http://www.craterfish.org/teamprodigies?pictures?2006/Jun

29 Jun 2006 (updated 13 Aug 2009 at 18:38 UTC) »
June 28th, 2006

I soldered the H-Bridge circuit that I designed. I noticed a major flaw in the circuit design - I had it so that either the left MOSFETs were both on or the right MOSFETs were both on which would short out the circuit and melt stuff. Fortunately I noticed this before I soldered the circuit. The new diagram is at http://www.craterfish.org/teamprodigies?pictures?2006/Jun, along with pictures of the finished motor controller. The heatsinks are set up in such a way that the entire circuit board will go inside a tube that will have air flowing through this. I may put a fan in, or I may just have an air intake on the front of the vehicle.

The motor controller is user-proof. It has two wires for the motor, a ground wire, +12V, +24V, a direction input, high control, and low control. The high and low control wires turn the power on or off to the high-side and low- side MOSFETs. The low-side power can be controlled with PWM. The high-side MOSFETs would be turned off for regenerative breaking, while the low-side remained on with PWM.

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