Hey everyone

I haven't updated this blog for a long time.

This is because I generally post the information on forums much more often than I post on this blog. 

When I post on this blog I kinda feel like I am talking to myself, plus I enjoy having people give me some suggestions on forums. 

So eventually I will update this blog (probably when I finish in a month or so), but until then please head over to my build thread on an S2000 forum. 

Located here : http://www.s2ki.com/s2000/topic/975497-wait-that-isnt-an-f20c/

Thanks for checking the project out :)

Differential Swap

Hey everyone
Unfortunately, since I don't update this as often as I wanted to, a bunch of information and pictures have gathered up but still need to be organized. To start sifting through all the data, I decided to tackle an aspect of the car I want to discuss and illustrate what I did and how I did it.

In this post, I will be concentrating on upgrading my drive train.

The stock S2000 differential is infamous for being weak and fragile. Even with the stock ~200Hp engine, the car has the capability of destroying its differential if you're having a bad day. Upgrading to a turbo system nearly guarantees eminent failure of the differential.

Stock S2000 Differential

Differentials are responsible for equally dividing the power delivered by the motor, to the two rear wheels (for a rear wheel drive car).
Generally, a transmission, a clutch, a torque converter, or all three, are sufficient in protecting a car's differential setup. As it just so happens, once the electric car conversion is complete, I will have none of those.

In addition to lacking substantial buffers prior to the differential, the two electric motor's are capable of producing 700+ horsepower, and 1500ft/lb's of torque under certain conditions. Specifications like these make stock s2000 differentials shudder in their sleep.

Consequently, since I was adding gratuitous amounts of power to the car, the differential needed to go.
A little research on the topic wasn't very hard, and I found out I had 3 options

1. Send my stock differential to be cryogenically treated by Puddy mod himself
2. Purchase an R32 Skyline differential
3. Purchase an 8.8" Ford Differential

I chose the third option.

S2000 Differential Vs 8.8" differential with explorer cap

Option 1 was a little too expensive for my tastes. Puddymod does amazing work, however I couldn't bring myself to pay the $2000+ for the work. Not to mention, even after I had the differential beefed up, I would have to find a way to adapt it to support Dana 1350 drive line components. However, the obvious advantage would be that I would be able to remove the differential, and put it back in with little to no trouble. This would have saved a lot of time, but its ok.

Option 2 was also rather expensive. A used R32 differential goes for ~$400 and are much more difficult to find than Ford 8.8". Another disadvantage would be that the gearing (rack & pinion gears) aren't easy to find. Lastly, the differential would have to be modified to fit the s2000, however (evidently) the axle flanges are compatible with the stock s2000 axles.

Option 3 was the winner. The Ford 8.8" independent differential was the perfect match for the s2000. Numerous reasons contributed to the choice. Gearing is abundant for the differential, the differential itself is practically indestructible, 1350 pinion flanges are easy to come by, and it is cheap! It just so happened that I was able to pick one up off craigslist for $75 about 10 minutes away. I really lucked out on that one.
However, there are some drawbacks to the differential. One major set back is that the axles are completely different, and had to be custom made for my car. Additionally, it requires custom mounting, and once installation began I realized that a major problem existed in the inability to install the axles without tearing down the entire rear end.

The (nearly) final product

In order for the 8.8" differential to fit, I needed to figure out how to adapt it to honda's existing differential mounting points. In order to simplify the process, I chose to reuse as much of the mounting hardware as possible. To do this, I ordered a Ford explorer differential cover, which greatly simplified the process of bolting the stock support arm to the new differential. With the differential back plate installed, I began fabricating.

Differential sans-rear cover

Using Autocad inventor, and Cambam, I created a simple drawing that I exported to G-code, and ran on my router. The router cut into a 1/4" aluminum plate which I had mounted on its table. I decided to get artsy with my work...

Here is the completed plate, once cut

todo completo

I ended up drilling the remaining holes on my drill press, since alignment of the differential was rather difficult. Ideally the differential would have been rectangular, with the pinion flange in the center of one end, and the mounts symmetrically placed on another end. However, the ford 8.8" is the least symmetrical piece of hardware in the entire car. Everything is lobside, uneven, and arbitrarily placed.

Eventually I got the plate drilled, and the stock mounting arm bolted onto it.
I mounted it in the car, and proceeded to make the front mounts out of some 1/8" steel. This was my first time welding anything, so I practiced a little before hand and dove right in.

Front mounts (notice minimal clearance)

Measurements were taken for the axles, and the data collected was sent to the Drive Shaft Shop, who promptly delivered some high quality custom axles to my door, big shout out to them!

Custom DSS axles

When it came time to sell the stock s2000 differential, I was contacted by a man named Ben Herne by email who was interested in my differential. Rather than giving me the full asking price, he offered to trade me an 8.8" limited slip differential, professional installation, and some cash for the differential. After looking up the name, it didn't take long to stumble upon his company, Puddymod racing. His work is revered as some of the best work in the industry. He builds the strongest stock s2000 differentials that have become parts of hundreds of cars.

I took a trip down to Bradenton Florida to have the LSD installed, and it turned out great! Can't wait to see how it works with the car.

After removing the differential, I decided that it was mounted too low in the chassis and was susceptible to touching the ground when going up large curbs etc. So, I chose to move it up about 2". I modified my 1/8" mounts, but ended up having to throw them out because I overlooked something.

A rather provocative view of the pinion flange 

The pinion flange for a 1350 setup is huge, far larger than the stock s2000 flange. The diameter of the flange almost overlaps the s2000's differential mounts. With the previously designed front differential mounts, the pinion flange had about 2 mm of clearance between the mounts. To increase the distance between the flange and mounts, I had to re-do the design. Rather than going out and up, I had to go straight up, and out.

A day or two later, I had completed the new mounts, and painted them.

New Vs old

I reinserted the differential, and made sure it did not rub or anything. Everything checked out well!

New mount

The last step was to install the stock axles. Another obstacle appeared here; the wheel hubs needed to be removed in order to install the axles. 
Some hours pass, the axles are installed, and the wheels are back on.
I took some additional time to take out the torque wrench and ensure all my bolts were correctly torqued. I don't want my axle flying off on the highway!

Buttoned up :--)

Since the rear end is completed, I went ahead and reconnected the brake lines, ESC sensors, and hand brake lines that I removed when I uninstalled the rear sub frame to remove the gas tank.
Dropped the car, pushed it, and the pinion flange rotates! Success!

Battery Pack design

Anyone who has followed my build has seen my previous battery plans. Initially, I had anticipated using 10Ah Headway cells. Then I switched to the blue 8Ah cells, since they yielded a lower internal resistance meaning less losses to heat and inefficiencies. Then, I switched to 8Ah cells with an even lower resistance, red 'high power cells'. 

The game plan was to mate 972 of these cells together, 9p/108s, for a nominal voltage of 345ish and 2000A bursts. 

I was almost certain the headways were the route I was going to take, however I decided against it in favor of some of the highly acclaimed A123 20Ah pouches. 

Alright, why? Because the cells are pretty awesome. Although their origins are unknown, they still boast some pretty impressive specifications. 

To get the same performance out of this battery pack, I will a 4s/416s setup, for 343v nominal, and 80Ah capable of 2000A bursts. 

Not only that, but the headway pack would weight about double what the A123 pack should weigh.

The only drawback to the A123 cells is their inability to be put into a pack easily. I originally designed a rather primitive pack, consisting of bus bars separating the cells, and the entire pack would be compressed via a threaded rod that would go through the cells. 

While this design would work, I had two issues;

1. The threaded rod would have to be some sort of nylon or ceramic. The nylon rod would stretch under heat, and the ceramic rod would be fragile.

2. The cost of the copper needed for the bus bars would be ridiculous. I calculated about $700 worth, using bars of 1/4" and 3/8" copper.

With that in mind, I went about designing another pack. In order to combat the expensive copper necessary for the first pack, I needed to design a pack that didn't rely on the cells connecting directly to each other, since that would call for thick copper to space the cells. I had always wanted to do something along the lines of the white zombie's pack, having the tabs bend over a copper bus bar, and then another bus bar being clamped down on these tabs. However, this wasn't practical using 4 cells in parallel. After a little finicking with my A123 test cells, I figured I would cheat, and treat two 20ah cells as one 40ah cell. Now I need 2 parallel (which is 4 cells), which would allow me to use the clamping system. 4 cells would need 8 slots, and I dont think the cell's tabs farthest from the central copper mounting bars would reach.

A couple of minutes in CAD got me this 

Simply by changing the design, I was able to reduce the cost of the copper significantly. With the new clamping design, I can use 1/8 copper bus bars, with more surface area. The total copper price for all eight packs will be around $223 (according to onlinemetals.com). 

I then optimized the design, and entered some more accurate dimensions for the final battery pack file. 

I decided to make the pack with a 1/4" polycarbonate top, so that I can see the batteries. It also isn't much more expensive than other plastics. I wanted to use 3/8", however the cell tabs would not be long enough to go through the plastic slots, and attach to the copper bus bars. 

The sides of the box will be 3/8" on the short sides and 1/4" on the longer sides. There will be half an inch of space between the cells and the edges, so there is some room for error. Foam padding will be placed in these gaps to secure the cells. 

Here are some pictures of the final design

I still need to add some copper bus bars to the pack, but I just needed the box dimensions for now. 

The hole drilled through the center of the copper bars will hold them to the polycarbonate top plate, while two more holes will be drilled on the sides of the same bus bar to secure it to the larger bus bar which will hold 2 groups in series.

From there, I contacted a couple of engineering schools around where I live, and found a place to CNC the top plate and the individual sides of the battery box.

I still have more to update, I will update soon!

Working out the final design kinks

Long time no update.

Truth be told, lots of informative and pertinent information regarding the build has been gathered,but I have been much too lazy to type it all up. So I will now dump it onto the internet!

I am still rather upset at the slow pace at which this conversion is taking place. While I work on the designing the car for countless hours each week, I can't help but feel like I am moving in place. I assume most builds feel similar, but darn. Oh well, with the motors nearly mounted and the battery packs finalized, the so called 'light at the end of the tunnel' can now be seen with a telescope. 

Anyway, here we go.....

Motors:

A serious milestone was passed when I was finally able to order a coupler for the two warp motors. I called probably 300 different businesses, trying to find a reliable and trust worthy solution to coupling the litte red monsters. The solution to all the chaos finally came when I gave up on locating an appropriately rated coupler, and purchased a $20 generic set screw coupling. 

It basically is a steel oxide coupler with a 2 1/4" outer diameter, and  a 1 1/8" inner diameter, with a keyway. Not much to it, but it is only rated to 2500 RPM and 100 Ft Lbs of torque. My car will be hitting a 5500 Rpm redline, and have a max potential torque of 1500 Ft Lbs of torque. Quite a disparity between the two specifications, however I am hoping for the best. In the worst case scenario, the coupler explodes while on the freeway, sending shrapnel everywhere and destroying anything in its path. But what are the chances of that *knock on wood*??

With the coupler out of the way, I had a U channel made out of a 1/8" piece of aluminum. I then had two 1/4" arms welded to this channel, which would be situated in the original motor mount locations. The large U channel came out surprisingly cheap, ringing in at $60. Seeing how cheap a large piece of custom bended metal was, I returned back to the shop to have the 2 aluminum arms welded onto the channel. I was then hit hard with a $350 bill. I have no idea how two small arms took $350 of welding, regardless I was kinda upset and purchased a new tig machine.

I went ahead and spent a little extra to purchase a better 'starter' model. 

With the new machine, I carried on finishing up the motor mounting. Unfortunately, I soon discovered that having a nice welder doesn't ensure good welds.

My first project was to weld up some steel brackets to hold my differential in place. I used stick welding to do this, and was surprised by how straight forward and forgiving of a process it was. Needless to say, I welded up the two brackets, and had the differential mounted back into the car in a day or two. (more on this soon)

All my good luck was forsaken later that week when I began aluminum welding.  I practiced on some scrap aluminum with relatively good results, however when the time came to weld two of the motor end place onto the U channel, my welding suffered severely. I could not get the base metal to melt, the filler rod would always bead up, I would constantly spoil my tungsten. It was simply a bad start. 

I never really got any better at it, and as a result the welds look horrible. But I suppose it works.
I feel as though my failure was due to the large shape of the U channel, which acted as a giant heatsink wicking away all the heat I was producing. 

Regardless, I was able to horribly weld the front most motor holding place, and I simply tack welded the back plate, so now I can drop it off at a welding shop and have them actually do it professionally. Two more plates will be bolted to the U channel, but will be removable to allow for the movement of the warp motors. 

With the motor positions finalized, I will be able to put the motors in the car and get an accurate measurement for a driveshaft length. 

I hope to have the driveshaft ordered by tomorrow, since my custom driveshafts are ready to ship! (more about this soon also).

Getting things into motion

In the world of physics, it is universally understood that a large amount of energy is needed to overcome the inertia and the friction an object is experiencing, in order to bring it into motion. After an initial velocity has been reached, less energy is necessary to maintain a constant velocity.

I hope the same holds true for my project. I have recently realized that I have had the S2000 in my possession for six months, and have not accomplished much more than planning and disassembly. After sitting down for a short period, and putting things into perspective, I realized that I have to accelerate my work. Summer is approaching quickly, and I need my car by then.

That said, I have begun to order parts, and design more in my free time. I hope that once I begin receiving parts, my work will go along quicker and I will be more prolific on the project throughout the week. Once I get the gist of the process, I pray the project will be completed in about six months.

/ End rant /

Now, to the interesting part!
Since the last update, I have completed a couple of small things.
After discovering the immense amount of space the soft top occupies, I went directly to removing it.

Originally, I had anticipated purchasing a hard top for the car, but after driving it while it had a gas engine in it, with the top down, I found my decision to use a hardtop or soft top fluctuating.
Replacing the soft top is expensive, but a hardtop is even more expensive.

After removing the soft top (which is extremely heavy), and finding an immense space available for batteries, I made a final choice to purchase a hardtop.

Since an OEM hardtop would have a cost rivaling that of the entire car, I will most likely go with a cheaper, more aerodynamic approach. A knock-off Spoon 2 piece hard top from VIS will most likely be the winner in this hardtop showdown. Not only will it make the car appear more stealthy ( :D ), but it will also increase aerodynamics, while still allowing for the space previously occupied by the soft top to be used for battery placement.

VIS Spoon Replica Top

What I hope the car will look like with the top installed

After much deliberation, and studying, I have decided to shy away from using an under/overdrive. Cost, extra work, and extra complications involved while using a transmission have been the primary deciders for me.

Instead, I will use a direct drive approach, coupling the motors directly to the rear differential. With this decision, it will be necessary for the weak stock s2000 differential to be replaced with a 8.8" Ford pumpkin.
A day or two after posting on craigslist proved successful, and I picked up a 8.8" with 3.73 gears for $75 from a man half an hour away from my home. Work has already begun on adapting the large chunk to fit into the s2000.

The 8.8 with cover removed

Some calculations showing RPM vs. MPH

A major effort to design a suitable motor mounting plate has been made over the last two weeks. I have done an innumerable amount of research on the topic, until I stumbled upon the John Wayland's dual 8" warfield design from late 2000.

John employed a simple U-channel design, constructed out of a single piece of aluminum to hold his motors in place. 

I seized the opportunity, and designed a common plate for my dual 9" motors, taking ideas from John, and introducing some of my own. 

While I have not completed the final rough draft, I have already a metal worker assisting me, and should have the basic U channel out of the shop by next Wednesday. 

John's common plate

Another view

Another view, without motors

My first draft of a common plate

I also purchased a single Kilovac Bubba contactor, its a lot bigger than it looks!

 More updates soon!