Ferrofluid Sculpture test 2

After buying some strong rare earth magnets I re-tried my ferrofluid levitating sculpture. The main problem is that the ferro-fluid moves to the poles of the magnets (top and bottom, with gravity favoring the bottom) and does not surround the sides of the magnets. It was also hard to get enough small magnets to fit under the main magnet (as they repel each other), so I had to include a screw in the middle to get the weight correct.

Note: Working with Ferro-fluid is dirty and messy. If magnets snap together they can throw dark oily fluid which stains just about anything. Be sure to have lots of paper towels on hand, jars/shields under/around everything, and don’t work in a nice room. Dish detergent and abrasive scrubbing will eventually get it off of most surfaces that are not porous. Wear disposable rubber gloves and use disposable pipettes. Wear disposable clothes. Don’t use any of your wife’s kitchen appliances or instruments that you can’t afford to replace.

Update: After floating under the magnetic levitation for 24 hours, the ferro-fluid became much less “spiky” and eventually the drops at the end of the magnets became spherical.

Also, cleaning ferrofluid from a magnet is almost impossible.

Controlling the Cricut Personal (desktop cutter) via Linux

Cricut personal cutter
I caught a deal on cricut.com where they were selling their original “Cricuit Personal Cutter” (refurbished) for $49.99 ($65 with shipping). This seemed like a very good deal to me, so I bought one. By itself, the Cricuit can cut specific shapes and letters from paper (it includes a free set of shapes/letters, and you can purchase cartridges to add more). I plan on using it to cut metal foil (one of the few things you can’t cut with a laser cutter, because it is reflective) and potentially make stencils. I may also be able to use it as a plotter using special attachments for pens. (Circuit board resist markers anyone?)

To make full use of it, I wanted to be able to cut arbitrary paths from my material, which means controlling the Cricut from my computer. Continue reading

Tracking individual battery voltages

Line graph that shows the voltage of six batteries dropping under load. All six batteries follow the same deep V pattern, staying within 0.1 volt of each other.

This graph shows the voltage (multiplied by 10, so 65=6.5 volts, and 50 = 5.0 volts) batteries 1-6 of my electric pickup while accelerating. My first battery (blue) is consistently 0.1 volt below the others, so I am keeping an eye on it. But this graph shows that although it is a 1/10th of a volt lower, it does not sink lower than the other batteries under load, so it appears to be holding up well so far.

The graph also shows off my new (to me) Pak Trakr system. The Pak Trakr system connects to each battery in your pack with small remotes that daisy chain together. Each remote monitors six batteries and transmits the voltage levels once a second to a display and optional serial data logger.


Ferrofluid Sculpture – test 1

Test 1 was not a failure. A Failure would have involved getting ferrofluid all over my clothes and/or workspace. However, I was not able to get enough ferrofluid to “stick” to the magnetic mount to get the weight up to the 74g needed for proper hovering action. Gravity pulled the ferrofluid down to the bottom of the screws and it started to drip off much too soon. It looks like I will have to augment the upper magnet with magnets on the lower parts to get the ferrofluid to surround the hovering part of the sculpture.

ferrofluid-test1

Adding range to a Dakota Alert WMT-3000 wireless driveway alarm

Inside of a wmt-3000 wireless driveway transmitter
This is a photo of the radio transmitter inside of a Dakota Alert WMT-3000 wireless driveway alarm system. The wire coming through the hole drilled in the bottom of the case and soldered to the base of the antenna extends out to a 27″ wire whip antenna. Note the jumper circled in yellow. This jumper has a “high” and “low” setting. It is set to the “low” setting by the factory, and the “high” pin has been cut off. I found that the range was extended by soldering the “high” (cut off) pin to the center pin.
wireless driveway alarm with wire whip antenna

New voltage gauges


This picture shows off my new flush-mount laser cut panel with voltage meters installed. These new gauges are Datel self-powered LED voltage displays (DMS-20PC-8-DCM for the red traction pack display and DMS-20PC-0-DCM-B for the blue accessory battery display). They are considerably more expensive than my previous gauges ($50 for the red and $59 for the blue) but have two major advantages. First, they actually fit inside the dash, so I can flush mount them instead of building a box around them. Second, they are “self-powered”, which really means they have their own DC/DC converter built in and draw power from the source they are monitoring. But, because each gauge has it’s own DC/DC converter, they are completely isolated from each other (something that my previous “isolated” DC/DC converter didn’t really do well.) Having all the power circuitry integrated into the gauge also greatly simplifies the wiring.


The gauges come with metal clips to fix them to the back of a panel, but the clips were too big for my opening. I improvised with a very close fit on the cutouts and some large rubber bands. If I ever need to replace the rubber bands, I just unscrew the four 6x 5/8 inch screws to remove the panel. (The screws are not exactly balanced on the panel as I was matching up to pre-existing holes.)

I wanted two different colors for the accessory and traction pack voltage, so I paid $9 extra to buy the blue LEDs for the 12 volt accessory battery. It turns out that this was a mistake. The blue gauge is much brighter than the red one, and at night it is blinding. I wired up a toggle switch to allow the driver to turn it off when driving at night. (The red gauge is just right, easily visible in the daytime but not too bright at night.) If anybody wants to buy a blue self powered voltage gauge for $50 including shipping I’d gladly sell it and buy a red replacement.

On-Dash voltage guages

I received a VWRAS2-D12-D9-SIP isolated DC/DC power adapter from Digikey and built an updated voltage gauge module with dual gauges (one for the 12 volt accessory pack, and one for the 120 volt traction pack). The gauges were slightly too large to fit inside the dash, so I built an enclosure out of craft plywood that sticks out flush with the bottom of the radio.
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120 Volt Charging Plug

A 240 volt cable plugged into a truck's gas cap area.

Our “new” electric pickup came with a 240 volt twist-lock connector where the gas cap would be. This is great for plugging into a 240 volt outlet, such as used by an electric range or clothes dryer, but we are primarily charging it with a 120v convenience charger. (So called because 120v outlets are more convenient to find. It actually takes about twice as long to charge using 120v so from a time standpoint it is less convenient.)

I decided to add a second 120 volt plug behind the fuel port door so that I could plug in either voltage cable. Continue reading

Building a PVC Vacuum Reservoir

a foot of 3" PVC pipe with end caps painted black.
The electric pickup truck uses a vacuum pump to generate vacuum for the power brakes (and move vents in the HVAC system). It has a pressure switch that turns on the pump when the vacuum drops to under 15 inHg and turns it off once the pump has raised the vacuum to 25 inHg. The current system has a small 3″ by 1.5″ PVC cylinder as the vacuum reservoir. As soon as you press the brake the pump turns back on, and cycles on and off relatively frequently. I wanted a larger vacuum reservoir so that the duty cycle on the pump would be longer (it would stay on longer, but also stay off longer) and so that even when the vacuum drops to 15 inHg I could still operate the brakes several more times while the vacuum pump was working.
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A Month Driving the Electric Truck

Watt hour per miles driven over our first 20 charges. Averaging around 710 Wh per mile

We have driven our electric S-10 pickup for a month now, putting 187 miles on it and charging it 20 times (averaging around 9 miles per charge). We used around 132 Kwh of electricity to re-charge it (13% of our total household electricity usage for the month) which cost around $13.20 (or 7 cents per mile). The truck is averaging around 700-720 Wh of power per mile driven. If we were paying $3.75 per gallon of gas and getting 20mpg on an equivalent vehicle, the energy price comparable MPG rating of the truck would be 54mpg. The chart above displays the watt/hour per mile calculation for our first 20 charges. As you can see, the numbers jump around depending upon where we drive, what route we take, what speed we drive, etc. We are also in the process of breaking in a new pack of batteries).
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