Corbin's Treehouse - Corbin Dunn, Santa Cruz, CA
Plug Bug

New Geared 36 unicycle wheel build

My geared 36 unicycle was breaking spokes nearly every ride. I’ve rebuilt the wheel with the same spokes quite a few times over the years. I would have to rebuild it when the hub failed or had some problem that caused me to send it back to Switzerland. Or simply because I was learning how to build wheels myself, and didn’t really know what I was doing (that was the first wheel build).

Here is a time lapse taken with my iPhone 6 of me lacing the wheel:


I also replaced the brake pads with a new organic pad set. They are a little tight, but brake pretty well! 694.3 miles on the cycle meter (mainly a note to myself on when I did this).

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Bathroom Vanity: Sanded, and starting to finish

I finished up the drawers. I used the Bessey clamps to keep things straight and tight, and also to pull close any gaps on the end:

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After that, some still had some tiny gaps…I mixed some sawdust and glue together and filled them with that.

Then everything was sanded with 150 and 200 grit paper:

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And the first coat of water based polyurethane:

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I was having trouble getting it to spray to the thickness I wanted. I think I’ll let this first coat dry overnight and sand it down with 200 to knock off high spots.

Plug Bug: charger repaired; back on the road

The bug is rolling again! About 39,800 electric miles. I asked Manzanita Micro why it failed and what I could do to prevent it from happening again. They said it “was something in the negative side of the rectifier bridge. possibly something in the ground.” — I’m not sure what that exactly means. For now, I’m going to limit charging the car at 20 amps. I had previously been pumping it up to the full 30 amps, hoping to get the rated 6kW of power out of it. I think that makes it have trouble…but I can’t say for sure. 

Here’s a picture from today while I was charging at Apple:

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I always open the hood to let the charger get some extra cooling. It tends to overheat and starts blinking its LED when I keep it shut. 

Bathroom Vanity: Taking shape

My bathroom vanity is starting to finally look like something. 

Here it is dry fitted before glue up:

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The process will be to put one side on

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The back, and then the other side:

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Then lastly the front can be slid on. It went together pretty well!


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Front door glue up didn’t go quite as well; I had some alignment issues. I forgot that the last time I made glued together doors I had made a right angle jig to clamp them too. This had allowed me to get everything aligned and clamped straight. The main problem I had here was I had flipped one board, so I had to pound it off and put it back on right — all while the glue was starting to set. 

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The drawer fronts are a solid piece of maple with a groove cut in with the router table:

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Next step is to make the drawers. I milled the wood to ?” and then used my jig to cut some half blind dovetails:

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Next I’ll run a ½” bottom groove for the drawer bottom. Then some sanding and glue up. Getting close to being done!



Bathroom Vanity Notes

These are mainly notes to myself on building my downstairs bathroom vanity (cabinet).

Face frame construction was normal pocket hole screws and works well for the face and back frame (back side seen here):IMG 4529

In the above photo, you can see the stopped groove for the bottom sheet of ½” plywood. I learned from prior projects to always stop the groove at the pocket hole screw locations. You can’t see the pocket hole screws, because they are on the back of the cabinet. The tongue will get trimmed these points.

On the plans and Sketchup model I didn’t draw in the joinery, thinking it was easy. I originally planned to tongue and groove the side panels together, and also use some pocket hole screws to hold it together; the screws would be impossible to see on the bottom raise, and on the top rail you will be able to see them, but you would have to stick your head in the cabinet. I was going to tongue the plywood and groove the the frame. I realized I had a flaw; if I grooved the bottom rail, it would intersect with the groove for the bottom plywood, and effectively allow the chunk to fall out. So, I ended up using some biscuit joints to do the job, which can be seen here:

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If you know woodworking, you understand you can ONLY do this with plywood, as it is dimensionally stable. If it was a solid wood panel, the glue up would tear it apart when it swells in the horizontal direction. 

Now, I’m not fond of this technique. The glue-up took a long time because of too much squeeze out. Plus, one side of the plywood had some small nicks from ripping on the table saw. It also took a long time to sink in the pocket hole screws.

I’d rather embed it by cutting a ½” groove. Originally I wasn’t going to do that because I wanted it flush on one side, but after playing with the inset I ended up not having it flush, and doing a small (less than ?”) reveal on the outer side. I have to do the other side the same way, as I already cut the plywood, but the door plywood is still oversize and will allow me to do it better. 

Finally, a picture with clamps:

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Kickback! and the bathroom vanity cabinet

I started planing some wood down to ¾” thickness for my bathroom vanity cabinet:

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As I was ripping one pice to width a small sliver came loose; there was a crack in the end of the wood, and as soon as it was free it caused some HEFTY kick back. Luckily I never have my body directly behind the wood while ripping, and the SawStop’s awesome splitter prevented it from actually kicking back. It pushed back in my hand about 5 inches. I am really happy with the SawStop. 


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I’m starting to get some of the pieces ripped to width:

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Next it is some crosscutting and then pocket hole screws.

Bug down! Charger broken (again – 3rd time)

Sadly, the electric VW bug will be taking some time off the road. Last time it was the transmission, and this time it is the Manzanita Micro PFC-30 charger. I didn’t even get a 1000 miles before another problem came up. I was really hoping to hit 40,000 miles and it is nearly there hovering a bit over 39,700 miles. 

Last Sunday I was charging the car and pulling about 27 amps. The charger should be able to pull 30, but quickly goes into a limit mode due to temperature. This happens no matter what the temperature is, and is just a flaw in the charger. It might happen due to the voltage of the car: the car runs at 154 volts, but charges somewhere higher, like 170V – I’m not sure as the exact voltage as the charger has no measurement for this and you turn a dial to adjust it. So, it is stepping down the 220v input to 154v. And, I know the charger is only about 80% efficient, so the extra energy has to go *somewhere*, and that somewhere is heat dissipation. 

The charger has failed several times:

First time: May 2011 – Charger Not Charging — Manzanita Micro repaired it (out of warranty) for $170. I wasn’t quite clear on why it failed.

Second time: September 2012 – Charger Failed again. – $213 to repair it, and they said the reason was from corrosion on the cables.

This time, I’m seeing the same symptoms as the first time; the charger is causing a ground fault, and flipping the circuit breaker that my EVSE is hooked up to (50amp breaker).

I opened the box..I think the bad part is underneath where I can’t see. It smells like magic smoke. 

I don’t have much choices for a replacement charger; it is by far cheapest to just get this one repaired, so I’ll send it back and have them fix it again. The EMW charger looks nice; it outputs 12Kw, and is a decent price ($2300) — but I can’t fit the 12x12x12” dimensions in my current location. And I don’t want to pay $2300 for a new charger, when I can get the current one repaired for a lot less.

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chargepoint energy stats for my bug

Since July of 2011 I’ve been using chargepoint for charging at free charging stations, and at work. Prior to my work getting J1772 stations, I would use a dryer plug outlet that was provided for EVs. Here is a screen shot of the stats for my use:

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10,673.912 kWh used in about 4 years. Mostly with the bug, but some with another EV (Jan/Feb ’15). This also doesn’t include other J1772 stations I’ve used that aren’t charge point (i.e.: the free stations downtown Santa Cruz), and it doesn’t include charging at home. 

The large gap from August to January was when the bug’s transmission was broken, and I was forced to drive another car for a while. The shorter gaps were probably vacations.


Bathroom cabinet: Free Sketchup model download!

Here is my downstairs bathroom cabinet design in Sketchup:

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A quick rendering:

Rendering cabinet


And placed in my bathroom setup:

Downstairs bathroom with vanity 2015 06 22 20115400000


Download the free cabinet sketchup model: Downstairs bathroom cabinet 2015.skp



Plug Bug: You are only as strong as your weakest cell

I had known for quite some time that I had a weak cell in my battery pack. My electric bug’s battery consists of 48 lithium iron phosphate cells. I use the eLithion battery management system with a custom display I fabricated along with some custom ardiuno code to show cell info from the CAN bus. I would routinely see one cell (number 9) sag heavily under load. 

One day I left work work (a 20 mile drive) with my pack at about 50% charged. At about five miles from work my low battery warning buzzer went off telling me that I had one cell that was fully discharged. That was my bad cell number 9, and I was only at 30% SOC once I arrived at work:

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The cell was down to 2.07v, which is well below the nominal 3.20 volts, and the “fully discharged” value of 2.7 volts. I had ignored the low voltage buzzer, and continued to drive car, taking more energy out and over-discharging it. I knew this might destroy the cell, but I was okay with that as I had a spare cell at home. 

Once I got to work, the BMS wouldn’t let it charge! It thought the under voltage condition was an error where it shouldn’t let any energy in (which is strange). Luckily, I could easily unplug the BMS connection to my charger, and let it charge for a bit:

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This pulled the voltage up to 2.70 volts, and let it normally charge:

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At this point, I knew that 30% state of charge (SOC) was my real world “battery empty” point. This one particular cell has lost 30% capacity in the 4+ years and 39,000 miles that I have been driven the car. I know the other cells aren’t as bad, as they don’t sag under voltage load, but this one bad cell is the limiting factor of my pack. If I continued to discharge it below 30%, it would cause the cell to die. That in itself wouldn’t be that bad, but I heard dead cells can sometimes reverse the voltage and suck energy out of their neighbors. I would also have to bypass it in my BMS, as it wouldn’t let the car drive with a dead cell.

I continued to drive the car for a month or so, and just didn’t let it get that low again, and it worked fine. But I really wanted that extra bit of range and capacity “just in case”. Plus, I had two spare good cells for this very reason.

Last weekend I finally did the work to replace the cell. I had previously used a volt meter to find out which cell it was (the numbering doesn’t seem to be related to anything I can figure out). It was a cell in the front trunk of my car, so I pulled out the module for it:

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I snapped the green strapping wires apart, replaced the bad cell, and then strapped the module back together.

This time, I used my engine hoist to pull the module out and put it back in:

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It was so much easier than trying to pull it out by hand (which I had done when I originally installed the modules!). 

The bug now has a bit over 39,100 miles. The transmission is leaking a bit of oil from the main shaft seal; I’m afraid it will eventually fail again.

Now, I need to do another capacity test with the pack and see how the other cells are doing. 30% loss over roughly 4.5 years isn’t that great…the cells forecast an expected 20% loss after 10 years of use when discharging to more than 20% SOC. I always did this, but I also always charged to 100% SOC (indicated by roughly 3.6 volts per cell). I think always charging to 100% has reduced the capacity. If I were to do the project again, I would write some smarter charger controlling logic to limit max SOC to 90 to 95% for most charging sessions, and only charge to 100% on the days I knew I would really need it, or would use the energy right away. Sitting at a high SOC for a long time isn’t good for the cells.




(c) 2008-2015 Corbin Dunn

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