Good news and bad news

September 28, 2010
I tested the flywheel coupler again - this time with the taperlock bushing seated fully on the motor shaft, and the pull from the clutch slave cylinder pulled the coupler right off. We need some way of stopping any lateral translation of the hub whatsoever. My first thought was to add in a bolt to the end of the motor shaft which would clamp the coupler onto the shaft. This would work great, and a few other conversion I have seen are using this method. Unfortunately it won't work for us, because of the way that the hub is welded to the flywheel - there just isn't room for a bolt. To make this idea work, we'd have to start from scratch with a new flywheel, bushing, everything = $$$...

So I think we mave have some luck using a pin. We'll take the motor and coupler to our machinist, and hopefully he can drill a hole through the whole thing and put in a pin to hold everything in place. If that works - we'll be up and running in to time.

Plus tonight, I'll be bringing over all of the boards to Electrocraft to have all of the MOSFETs upgraded too. Graham will be coming to help out as well, so we should be able to get through the lot of them in no time.

I also started building the covers for the battery packs using clear acrylic plastic and aluminum edging. These covers will keep out water and foreign objects including stray wrenches and wandering fingers. We have come to appreciate just how powerful these batteries are.

At this rate, we might have enough time to spruce up the appearance of the 944 before EVFest too. It's still unlikely that we'll be able to drive it there, with all of the problems getting insurance. Still, being able to have a tour around the parking lot would be nice.
 

Clutch and battery issues

September 25, 2010
There have been a few very frustrating setbacks lately, involving the two most important systems: the battery and the motor coupling.

I'll start with the motor coupling. We had started off with a simple set screw coupler, but that introduced a fair amount of wobble with the single setting pin. Plus, the other half of the coupled that was welded to the flywheel was slightly mis-aligned, further increasing the wobble. We then had a machinist cut out the old hub and add in a new one for a taper-lock style coupler. He also made sure that the hub was centered and aligned properly before welding. This is a much better system, but it also changed the way the flywheel sat on the motor shaft. We were using a 1 1/2" spacer for the bell house adapter, and with this thickness, the taper-lock bushing would slide fully onto the shaft. We tried tightening it as much as possible to see if it would hold, but as soon as the clutch was depressed, the clutch/flywheel assembly slid down the shaft instead of releasing the pressure on the clutch disc. I have now removed a 1/2" of the spacer (luckily we're still using 1/4" plates of aluminum instead of a single solid milled piece) and the taper-lock sits fully on the shaft. I'm still worried that the assembly may slide on the shaft. One of the coupler kits online has a piece that threads into the end of the motor shaft and holds the bushing in place. With the 944 shaft though, it has a tip which needs to slide into a pilot bushing at the center of the flywheel - which now will slide right into the end of the motor shaft.... So there really isn't any room for a threaded bolt to hold the flywheel on. If the taper-lock isn't strong enough to prevent the flywheel from sliding, it'll be back to the drawing board, and probably a new flywheel. I'm not sure how many times it can be cut and welded without becoming weakened or warped.

Also, the BMS has been causing problems again. I thought that it was the resistors that we'd been having problems with before, but those checked out ok. Now, the mosfets that switch on/off the bypass resistors are burning up. We had made a few changes to the bypass resister values during our initial testing, and now the current going through these mosfets rose from about 1.5A to 4 or 5A. With the voltage drop across the mosfet, this is now about a Watt which the little switch needs to dissipate. It's designed to handle up to 12A, but not for sustained periods of time. Plus, they are located very close to the bypass resistors, which reach upwards of 80 degrees C under bypass! Yesterday Darius found a larger mosfet which had much better heat dissipation, and replaced a few of the old ones. We then did a test see just how hot these components were getting. The bypass resistors hit 75-80 degrees pretty quick. The new mosfets reached about 60, which is within their limits. The old mosfets however quickly got up to over 120 degrees C! No wonder they were burning out on several boards.

Clearly, the by-pass resistor design has its flaws. We'll replace the mosfets on all of the boards anyway so that I can start using the batteries, but Darius and I will start designing a new BMS starting next week. 

I'll be testing the flywheel coupler today, and hopefully I won't have to redesign that too.
 

Root Cause Analysis

August 19, 2010
Last week we were taking great strides towards completing the 944. The motor and clutch were installed with the new and improved flywheel/coupler. The batteries were installed and wired up. All of the accessories were mounted and wired as well. We had our first trial run using the full battery voltage and the controller. After a slight polarity issue from the key-switch, we had ignition (contact closure actually). With the drive wheels lifted off the ground, we spun up the motor - and had some seriously noisy shaking!

With our latest flywheel design, there was no way we should be getting vibrations like this. What seemed harmless at 12V was disasterous at 180V. So we had to remove the entire system to do root cause analysis.

To make a long story short - the clutch pressure plate had a broken spring! Our flywheel was spinning nice and true, as was the clutch/pressure plate. But, once the drive shaft was insterted into the system, the pressure plate's broken spring was unloading 1/3 of the clutch disc and essentially twisting the disc, transmitting a lot of movement into drive shaft/transmission and the rest of the car. At least it wasn't our flywheel design.

So yesterday I picked up a good-used pressure plate from Nineapart.com so we should be up and running again in no time.

While the batteries are back sitting in my living room again, it may be a good opportunity to take care of waterproofing the battery racks in case we get stuck driving through the rain at some point. We made a few structural modifications to the car during the last disassembly of the system so that we can now assemble the battery packs outside of the car and use the crane to drop in the whole pack all at once. This should save a lot of time if we ever have to remove the batteries again.

Two steps forward and one step back is our new motto.
 

Minor technical difficulties

July 23, 2010
In the previous post, I mentioned a slight vibration in the clutch assembly.... well, it quickly became apparent that we had to fix this vibration. There was a lot of testing, brainstorming, and trial solutions, but eventually we realized that there was no fix-it solution - we had to cut out the coupler and start again. The problem was in the weld between the shaft coupler and the flywheel. It turns out that the coupler wasn't completely flush and level with the flywheel when it was welded on. Now, considering that the welder knew that this was for a spinning application, I would have thought that he would at least have clamped the pieces together before welding. However, I'll take the blame as I never specifically asked for clamping and levelling. The result is a large "wobble" as the flywheel spins. The term is called runout. Often, the required runout tolerances are in the 0.1mm range or smaller, and we had a runout of 2mm! This, aided with poor tolerances of the shaft coupler on the shaft (very slight play prior to fitting the set screws) made for a very poorly spinning flywheel, and a ton of vibration. We're going to do it properly this time at a machine shop where they will make sure that everythink is centred, balanced and fitted precisely. During the brainstorming process we also came up with some ideas to improve other parts in the system, which we will be implementing as well. The parts are at the shop today and we may be able to do a trial run early next week. At least we're finally moving the right direction.

We also spent a lot of development time lately on the BMS for our LiFePO4 batteries. These batteries have a few unusual characteristics, and it has taken a while to learn their quirks. We have also made a numer of design changes to the BMS circuit boards to improve measurement capabilities and to handle real life charging scenarios better. We are still using a top-balancing system, which is certainly not ideal. However, we are not strictly enforcing the top voltage of each cell. The cells that reach the top first will slow down to let the others catch up, but only within about a 0.1V to 0.2V limit. This, along with a time limit in absorption mode should allow for some top-end imbalance in the cells. Couple this with regular (not sure how often yet) bottom balancing cycles, and we should have a robust system. We had to modify some component values in order to handle the extremely unbalanced state that we started with after we charged a few cells during board testing. The last change in resistor values will be completed early next week, and then we can started doing some actual charge/discharge cycles. This will allow us to test our new controller as well using the test facilities at Electrocraft.

In all, progress is slow, but we are fixing every problem as it arises, and learning valuable lessons as we go.

 

First Run

May 31, 2010
Well, it's been another long gap in the blog - but there has been lots of progress with the car. Yesterday, we finished installing the clutch and the engine mounts, and got the motor secured into the car. The battery system isn't ready yet, so we went for a test drive using the original 12V lead-acid battery! It was a low-speed excursion, but the acceleration up to 6kmph was really fast! There was some minor vibration in the flywheel, which we may need to remove at some point.

The BMS board have been built, and now the testing begins. Hopefully in a week or so they'll be ready, and the batteries can be fully charged for the first time.

Check out the video of our first drive in the SMEV944 in the Pictures section.
 

Engine Meets Car

March 2, 2010
A long time awaited, the engine has finally braced the engine bay where it will sit powering our 944. There is plenty of space for the batteries to sit in front of and a top the engine. We used a piece of 2x4 to hold the engine in place for now as we will begin to measure and accurately cut and drill the holes for the aluminum that will replace the wood.

We continue to plug along cleaning the interior using loud and obnoxious tools to grind away any remaining glue which, to our surprise was distracting to say the least for the shop owner. Most of the gritty work however, is complete and we are now really ready to focus on all the mechanical features so that we can move back to our garage as soon as we can.

The batteries are due to arrive March 5th and with the Brackets near completion and wires to be purchased soon, we should be well on our way to completing the car 1 month before schedule. This doesn't include any cosmetics of course :) We want to leave that to the end.

It's great to finally see the engine where it belongs. Please browse the pictures section to view the engine placement and other new updates.
 

New Interior

February 21, 2010
So, work has been progressing steadily on the 944. The interior has almost been fully cleaned out, including the pesky sound deadening material which is turning up in places all over the car. A heat gun and chisel are making the removal of the insulation straightforward, but still time-consuming. Apparently there is almost 100lbs of this stuff in the car! Talk about overkill. Yesterday I removed the rest of the interior paneling and dyed it all black. With the black door panels, the car already has a lot more class.

The clean-up of all of the wiring is almost complete as well. Whatever is left is getting tidied up and tucked out of the way. I'll have to do some thorough testing of all of the features before I pack it all away too carefully. So far though, it looks like all of the lights are working properly. The gauges may need some tweaking to work properly. 

I think that I have also figured out a solution to hub/adapter problem. I purchased a keyed hub from Princess auto which fits the Warp9 motor perfectly. I also bought a pulley gear which is designed to be welded onto the hub. I will have to cut off the gear teeth, and then drill all of the holes to properly match the flywheel. For the adapter plate, I met with a local machinist who's going to see what he can put together for me that will work. It's not going to be as pretty a solution as a custom fabricated plate that I could buy online, but it should significantly less expensive. 

Hopefully Graham will snap a few more pictures of the progress this week. It's all starting to come together. It's really the interior work that's taking up more of our time so far unfortunately, but the end result will be worth it.
 

News Travels Quickly

February 9, 2010
I received an email from DEVA (Durham Electric Vehicle Association) and am glad to see that there is a lot of interest in our business. Many members are interested in converting their vehicles and would like know more about us. We will be scheduling a presentation at the Durham College Whitby Campus for DEVA on March 4th, 2010.
 

Tools Make Life Easier

February 4, 2010
The battery brackets that will be mounted in the engine bay and rear passenger seat are now starting to take shape. WIthout a shop to work in and use of specific tools such as a drill press, metal cutter this job would be much more difficult but with the help of these items the brackets are coming along nicely. A strong and steardy design has been made using a few simple pieces from home hardware. The brackets seen in the picture are to carry 18 of our lithium ion batteries, a case will be designed to contain 4 cells each and will sit on two rows. Hopefully, the rest of the brackets will be in place by the end of the week!

 

Finally - some progress!

January 25, 2010
Well, this weekend really began our adventures in building an EV. Up until now, our work has been completely destructive: removing parts and pieces that we would no longer require. On Saturday however, we installed our first new part - the vacuum pump! It may not sound like much, but it's really gratifying to finally be adding new parts into the Porsche. Of course, we're still working on sanding and painting the interior and engine bay, but having a functioning part just makes the difference. We found a nice spot for the pump right underneath the brake booster, which keeps the tubing lengths very short, and also won't interfere with any of our planned battery locations.

All in all we only worked for about 8 hours over the weekend, but we got a lot accomplished in that time. I'm thinking that the 200 hour estimate for a conversion may not be too far off the mark for us.

Next weekend we'll be taking some photos of the 944 in its new home, and adding some photos of the vacuum pump too.