Monday, November 14, 2011
EleCobra - The Thrill of Victory, and the Agony of The Feet.
Sadly and painfully behind on my blogging duties, it is probably poor form to attempt a remedy with one massive update. But we do what we can. We HAVE been a bit busy with the roundup of the EleCobra prototype for Aptima Motors.
Recall, if you will, that I was vaguely disappointed in our performance at the local airstrip with the EleCobra. As it turns out, justifiably so. I'm pleased to report that we had quite a bit stronger car in the box than was immediately evident.
The week before last we took the EleCobra to Slingblade Performance in Anna Illinois to do some dynamometer testing on their Dynojet system. The results there were also disappointing. But we mounted a video camera behind the car and shot the actual gages up close while the acceleration tests were performed.
On return, I did something so gruesome I scarce recommend it. I exported the Winpep data in 100 msec chunks. We shoot our video at 29.97 frames per second and so 1/10th of a second corresponds to 3 frames of video. And so I loaded the videos and cycled through the runs 3 frames at a time, noting amps, volts, temperature,s etc from every gage on the dash, three fluke meters, and the Netgain Warp Drive Interface Module.
This is beyond watching paint dry. It's self abuse.
But it did pay off. We could note, for example, that not only were we NOT getting the calculated power, but apparently we weren't asking for it. The throttle input never exceeded 80% command.
Recall that we had struggled with a type 23 error reported on the Netgain Warp Drive Industrial. Mr. Bohm was prompt in providing us with a firmware upgrade on the controller. Better, the process of updating firmware was actually pleasant. Mr. Bohm sent us an e-mail with an attached file. We pulled the tiny SD micro card from the interface module and mounted it in an SD card adapter, and plugged it into a desktop computer. We could then copy the file onto the card.
We then reversed the process, inserting the card into the Interface Module. A simple menu item allows you to update the firmware to the controller, and in fact you can even update the firmware in the Interface Module itself if need be. The entire process from e-mail to updated controller was probably not eight minutes.
The Interface Module is a very handy way to set configuration items on the controller, but there really aren't very many. You get motor amps and volts limits, in forward and reverse. You can clear errors, and read errors. There's a "frame leak" option. And not very much else.
But you CAN select your throttle type. You don't get to change much on it, but you can select it. Our throttle is the LOKAR PEDAL the last option on the list. We believe when we updated the firmware we reverted to the default, CTS which is the FIRST item on the list.
So we were running the car error 23 free finally, but with the WRONG pedal. This had the unfortunate effect of lopping off the top 20% of our available power.
The scary thing about all that is that without all this testing, we never would have known. We would have been vaguely disappointed in the Netgain 11HV, the Warp Drive Industrial, and the EleCobra. But it ran well, and we could have gone for years. As a first prototype, we would compare it to WHAT? What SHOULD the power have been? My napkin scratch?
The central issue with one-off custom cars and prototypes is you never KNOW when you are done. Now that we've found the pedal issue, is there MORE things we are missing? More tricks that could this dramatically improve performance?
Our zero to sixty time dropped from 6.8 seconds, which isn't as good as Speedster Redux, to 5.8 seconds - making it the fastest car on our lot. That's a 14.7% improvement. What ELSE is in the car that will give me another 10% say? Scarey thought.
This week, we returned to Slingblade and things got better.
You can also see the results in the graphs below and I'll include a link to the actual elecobra.xlsx EXCEL FILE for the Cobra so you can see the data. There's actually a LOT more data in the file than we graphed and you might find some of it quite interesting.
I'm going to hear howls from the Dan Friedricksons and other lesser intellects on the disparity between the data from the fluke meters and the Xantrex and the Interface Module. Here's a clue. Each device has a different "sample rate" and we are snapshotting the numbers in 1/10th second slices. If you slide the numbers, they're all good, just not in precise line in all cases.
Since we insisted on publishing everything we did on the EleCobra, Aptima Motors, which has plenty of secret plans, has avoided making us privy to all of them for obvious reasons. But Bryan ANderson claims they have already put two additional chassis into work. They are going to integrate the battery boxes a little bit better into the new frame. And they are going to do a carbon fiber body for the vehicle. Bryan believes he can slice 400 lbs certainly, and potentially as much as 500 lbs from our 2961 curb weight. With a 5.8 second zero to sixty now, imagine the improvement with a 17% weight decrease. This should also have a dramatic impact on our 120 mile range. And I think he mentioned they are going to sell these cars completely finished at $85,000.
What I found very surprising was a rather significant level of interest from his EXISTING customer base of Cobra owners in the project.
I didn't have any doubt at any point that we could make the car roll forward using batteries and a motor. Frankly, no miracle there. Really anyone CAN do this. If you want to take an existing car and make it drive on batteries, the stuff is there.
Naturally, we wanted to do it with new and interesting components to make it interesting video. But my concern from the beginning was that the resulting car be "Cobra-like". And I struggle to define what I mean by that. Obviously it would be a new and different thing powered by LiFePo4 cells and a magnetic motor. But could it be done incorporating the feel and mystique and sense of this car, which has such a history and such a community of enthusiasts who so deeply feel the Cobra gestaltd?
Bryan Anderson claims to have built 2700 chassis in 25 years, the majority of which are Cobras. He seems to think so.
Our mission was to take an existing car as it was and convert it to a working prototype electric drive car. In this particular adventure, the loop is continued. Now Mr. Anderson can take what we've done, and go BACK to the beginning of the process. By making some fairly dramatic changes to the chassis, he can take off weight and do a MUCH improved positioning of the battery cells. With carbon fiber, he can lighten the body and if he dares, alter the front end to eliminate the aerodynamically perverse open front face of the car - vastly improving the admittedly poor aerodynamics of this particular model.
There are some more refined improvements available as well. If you are disappointed with our horsepower numbers, you probably ill understand what horsepower is. Our torque was very good, but it WAS a little constrained to the lower end of the RPM band - limiting somewhat the HP number you read on the dynamometer. Horsepower is an expression of radial torque RPM corrected. Simply increasing the voltage 20 volts would widen that RPM band substantially. By incorporating the boxes more integrally into the chassis, that is a very possible improvement.
We were at that under 500 ft lbs of torque. The Tremek TK600 transmission is the big guy in that line and rated for 600 ft-lbs. On reflection, it is POSSIBLE that a lighter, lower friction T45 or even T5 transmission MIGHT make the grade - decreasing our drivetrain friction losses as well as overall weight. The same can be said of the entire rear differential and axle assembly.
The production costs of the EleCobra are simply too high to be a viable vehicle in my estimation. But Aptima is intent on it and at $85,000 it would certainly be an interesting offering. With the changes outlined above, this would truly be a performance car by any measure, and I can say the view from the cockpit did grow on me over the course of this project. It will be very interesting to see this develop.
Meanwhile, we're back on the Elescalade and a couple of new projects. As described in the second video, we are taking a close look at Factory Five Racing's 818 World Car concepts. This is a two seat mid engine spyder sports car using the universally and globally available Suburu parts in either left OR right hand drive. David Smith intends to reach a younger customer base with this and enhance his already notable export business - he calls it a "World Car." Better, he is looking to a $9900 kit car price with a completed vehicle possible at a smooth $15,000.
This is very attractive. We can't make it electric and stay within $15,000. But an electric version of this modern, very aerodynamic and lightweight (818 refers to kilograms wet) could be very attractive at $25,000 or even $27,000 all in. If we could find a suitably NEW and interesting motor and controller combination, and perhaps a suitably new and exciting battery architecture to match, this could be the ultimate kit build electric car at a price more of our viewership can afford than say, the Elescalade.
I guess the question we would have is should we go for max range/performance or attempt a dramatic price breakthrough on such a build? Viewer thoughts on this would be welcome.