Monday, December 16, 2013

Rumination on Electric Drivetrain for CarBEN EV5

The background on this is I was able to be at the X-Prize Knockout Round as a guest member of the Edison2 team, and while I was there I meet and talked to many of the people, and to see what they had built, and all the effort and passion that went into it.  Jason Fagone has written a enthralling and detailed book about the X-Prize, called 'Ingenious' and he and Kevin Smith of Illuminati Motor Works are touring with the IMW 'Seven' electric car.

Seeing the IMW Seven and talking to Kevin Smith and to some of the folks at the MIT Electric Vehicle Team has got me thinking more about the main electric drivetrain for CarBEN EV5 - which is a 5 seat electric car that I am currently building.  I've been concentrating on the design and how to construct it, so this is a first take on the drivetrain components:

I like the looks of the BRUSA SSM1-6.17.12 along with the Getrag GX629 6.4:1 EV Transaxle assembly. That puts the ~ 5,500 RPM which is the peak efficiency of the motor right about 55-60 mph (depending on the tire diameter you use).

No rare earths used and lower cost (though certainly not inexpensive), and a compact package (roughly 11" x 20"?) with no 90ยบ turns - we may have a winah!

The batteries used in Seven are the Thundersky (now CALB) 100Ah cells.

I can fit 106 of these in CarBEN EV5 (Seven has 99) and Kevin Smith swears by them and their ruggedness. That would be ~ 35.3 kWh and cost roughly $16,000. They use no BMS and do a "bottom balance" and have stopped seeing stress that occasionally caused the cells to swell.

I had used the EiG 20Ah pouch/prismatic cells in my planning and I could probably fit about 50 kWh into the compartments in the floor. FVT has an innovative BMS system that shunts the excess from one cell to another cell that is still charging; rather than to ground - as I understand it.  This should be more efficient than ordinary BMS.

I looked briefly at the A123 cells, and these are wider than would easily fit in the battery compartment I have in CarBEN. And they are very hard to find, if not impossible.

A choice for charger is still vague. Seven has a Manzanita, and it works well. They disconnect it on the inside, so that regen doesn't blow it out.

One of the MIT EVT people has put me in touch with their Porsche guy, and I have asked about getting the rear suspension from a 914. He is a busy person (post grad?) and I will wait and see if he can help me. Up until now, I've been thinking of using the front suspension of a Saab 900.   But I'm also going to look at the Neon front suspension that Seven uses (in the front and back), though I don't think it could fit in the back of CarBEN, and I don't need the Prelude rear wheel steering; as the wheelbase of CarBEN is significantly shorter.

It looks like all this hardware will cost $35-40K, which is actually about what I was expecting.

The Illuminati Seven sets a high standard for efficiency: it uses just 129Wh/mile at ~60mph, and it has a 220+ mile range at 60-70mph.  The EPA rating (tested by Chrysler at their proving grounds in Chelsea MI) for 7 is 207MPGe.

Which is something to strive for.

Here's the entire build in pictures, so far:

Here's my blog post of the construction process so far, with links to the previous posts on the design process:

And pictures of the first public showing, at Earth Day Fair in Framingham MA:

And my YouTube channel:

Monday, April 22, 2013

CarBEN EV5 Construction

This is the final version of the SketchUp model of CarBen EV5, which was used to generate 2D CAD drawings.  Those drawings were then used to generate the G-Code files for the CNC machine that cut the XPS foam sheets.

View from above showing the driver in the center

Views of the computer 3D SketchUp model

Vertical Cutaway front to back showing battery cells in floor four of the passengers
Plan Cutaway through the roof showing the five seating positions and the aisle way

These are all the profile sections cut through the model, and all of the layouts of the 2' x 8' x 1" thick foam sheets.  For most of the sheets, I cut two copies to make a 2" thick layer.
This is the PhlatPrinter 3 which is a 3-axis CNC machine I put together from a kit that I used to cut the 1" x 2' x 8' sheets of XPS foam.
I cut about 95 sheets of XPS foam - on a good day, I finished 10-12 sheets.  The pieces use jigsaw joints and I glued them together and then stacked the layers, forming a "stair-stepped" core of the chassis.

These are the first pieces ready to have the jigsaw joints glued together

I used 1/2" wooden dowels to align the layers as the glue dries.

Building up the front of the car, layer by layer

Bricks used to press glue surfaces together while the glue dries

Beginning the shaping process, using Stanley SurForm rasps

The rough shaping continues...

Nose of the car in approximate position

Adding more layers - the dashboard and the front of the battery bays and the placeholder front wheels

The base of the windshield place holder

CarBEN EV5 Ranch?
The first four feet of the front
Next section building up layer by layer
The first six feet of the CarBEN EV5 ready to be joined up - clamping with a ratchet strap and lots of weight required as the glue dries.

I built a level platform to add the rest of the chassis one layer at a time

The beginning of the main hatch door opening

The front half of the CarBEN EV5 chassis sitting in it's proper position.  You can see the battery bays getting larger
Sitting back on the platform getting 6"-8" glued on a typical day

8' ladders now required to get to the gluing level

I constructed a temporary shelter that is high enough for what will end up as a 12' high stack of foam layers!  The front 2' of the nose will be glued on after I don't need access to the front.
Last couple of layers of the very back/top of the chassis
Last layers of the rear bumper glued in place and drying!  I worked from a scaffolding platform on 8' step ladders, and some 12' high step ladders, as well.
All the major gluing is done - the hatch door and wheel skirt panels, etc. left to do.

CarBEN EV5 Open Source Project Goals
  • Open Source means shared ideas and shared improvements – anybody can build one.  Creative Commons (instead of Patents) gives attribution but lets ideas get used as much as possible.
  • Build working Prototype to test efficiency and improve construction methods
  • Practical and safe and highest efficiency possible using renewable energy
  • 300-400 Miles Range on Single Charge using ~55kWh lithium battery, <150Wh/m, >224MPGe
  • Coefficient of Drag (Cd) <0.15 with 25.1 sq. ft. frontal area = CdA <3.77 sq. ft. (better than GM EV1)
Design Innovations & Key Features of CarBEN EV5
  • Tapered Shape required for low drag w/ narrowed rear wheel track, covered wheels, smooth underside, crisp trailing edges aka Kamm back, wheel strakes, passive air flow through cabin
  • Thermal insulation integral to chassis and dual layer windows, heated vests for passengers, slim ergonomic seats allow for air flow saving space and weight
  • Center Position for driver for increased crash protection and better use of interior space, three ~6'-4”+ people, one ~5'-8” person, one ~5'-0” person
  • All LED lighting, ideal ecodriving design, battery pack in floor for low Cg and better handling
  • Side Video Mirrors for reduced frontal area and lowered Cd
Electric Car Advantages
  • Energy Independence – No Oil from Foreign Countries & No Military Required & money stays in Local Economy
  • Cleaner and cleaner energy over time as we transition to Renewable Energy & lower cost over time
  • No gas, no idling, no oil changes, no tuneups, no exhaust system, no multi-gear transmission, no clutch or shifting, lower brake wear because of regenerative braking, virtually no regular maintenance
  • Very low energy costs – 2-3¢ per mile vs ~15¢ per mile for average 23MPG car saving ~$12,000 per 100K miles @ $3.50/gal gasoline + ~$3,400 savings on regular maintenance per 100K miles = over $15,000 savings
  • Very quiet, very smooth, quick acceleration, smooth torque, great for typical daily driving
Electric Cars & Plugin Hybrids you can buy today

  • Nissan Leaf – 116MPGe, seats five, ~80 mile range, as low as ~$22,000 after tax credit
  • Mitsubishi i MiEV – 112MPGe, seats four, ~65 mile range, as low as $21,625 ATC
  • Tesla Model S – 89-95MPGe, seats five (+ two optional), ~208-265 miles range, ~$60,000 for 60kWh model and $70,000 for 85kWh model, both ATC
  • Ford Focus Electric – 110MPGe, seats five, ~76 mile range, ~$31,700 ATC
  • Toyota Prius Plugin – 95MPGe/50MPG, seats five, ~11 miles in EV mode + hybrid, ~$29,500 ATC
  • Chevrolet Volt – 98MPGe/37MPG, seats four, ~38 miles in EV mod + hybrid, ~$31,645 ATC
Coming Soon: VW e-Golf, Smart ForTwo Electric Drive, Mitsubishi Outlander plugin hybrid, Fiat 500e, BMW i3 & i8, Ford Fusion Energi & C-Max Energi, Subaru Crosstrek Plugin Hybrid, Chevy Spark, Cadillac ELR, Tesla Model X, Honda Fit EV & Accord Plugin Hybrid, Toyota RAV4 EV, Infiniti LE, Volvo V70 & V60 & C30, and more...

I brought my CarBEN EV5 prototype to the Framingham Earth Day Festival this past Saturday (April 27th) on the Framingham Center Common, and it was every bit as good as I could have hoped for.

Previous blog post on CarBEN EV5 design:

Build thread:

Here's a longer, more detailed walkaround video:

I tried the stabilization in the camera, but it still needs the YouTube processing...

It's got it first dirty bird, and there are glue drops and runs, and rough edges...  My son will be helping me move it back into the shelter soon, so I can continue smoothing.  The left side in particular needs a fair bit of work.  They all show up much more readily in the full light of day!

This is how I am using the longboard sanding tool I bought from Jamestown Distributors.  It is a tool normally used on boat hulls, and it is nearly perfect for this, too.  The swirling motion and figure 8 motion tend to avoid any gouges or divots.

I was able to even up the surface so that the several low areas are largely gone.

I wish that my video camera had a wide angle lens - I had to position it quite far away, and I hope things so up clearly enough.

My latest purchase is the windshield and wiper system from a Smart Fortwo: