sustainable transportation design
After several attempts to restore function, at long last the AC Forum is back online. If you’re incorporating an AC drive into your EV conversion, this page will serve as a great resource.
Also, if you need back-end web page work at a reasonable rate, check out HLiNaK. I’ve used their services and am very happy with the results.
Though the eMR2 couldn’t be there, this Saturday’s Power of DC autocross event hosted a variety of factory and conversion EVs from all over the east coast. Three Teslas, including a Sport model, tore around the course with the Sport model setting fastest time of the day by rounding the course in under 18 seconds. Though the Teslas set the pace, it was a Mini-E that set the record for the most runs as it rounded the track nearly all afternoon.
Among the conversions, surprisingly it was a VW Rabbit pickup that cut the cleanest path around the cones despite it’s nearly 3/4 ton of batteries. A sunburst yellow Destiny 2000 (based on a Pontiac Fiero chassis) gave it a run for the money but the Rabbit’s driver was an obviously experienced hand who could make the most of his car’s abilities.
Other interesting vehicles that ran the course included the WVU Formula Lightning racecar, a Porsche 944 conversion and a daily driver VW Jetta. Below the pictures are the times for all the day’s runners, courtesy of Chip Gribben.
AUTOCROSS
Saturday, August 29
place/et/driver/vehicle/runs
Production EVs
1) 17.761 – Dave Bolling – 2009 red Tesla Sport (31 runs)
2) 17.979 – Don Auker – 2008 blue Tesla (44 runs)
3) 18.718 – Tom Jamison – 2009 prismatic blue Tesla (19 runs)
4) 19.316 – Ken Barbour – 2009 Mini-E (64 runs)
5) 23.289 – Bryan Murtha – RAV-4 EV (5 runs)
Conversion EVs
1) 21.214 – Dave Cover – Porsche 944 (6 runs)
2) 21.948 – Alan Arrinson – VW Rabbit truck (13 runs)
3) 22.648 – Doug Stansfield – White Hyundai Tiburon (5 runs)
4) 23.441 – Bob Rice – VW Jetta (11 runs)
5) 24.842 – West Virginia University – Formula Lightning (9 runs)
6) 26.643 – Joe Lado – Destiny 2000 Fiero (24 runs)
Finally, this past week I was able to enjoy commuting in the eMR2 v2.0, equipped with a new single speed transmission, motor coupler and batteries, every day.
There’s still some mechanical work to do, such as address the howling rear wheel bearing and sticky CV joint, but all the EV conversion components are performing as designed.
Pictures and video coming soon, as well as a report from Power of DC happening tomorrow in Hagerstown.
A couple years ago when the eMR2 was still in the design stage, there were two competing coupler designs: a simple dual spline coupler (described in a previous post here) and a more complex design that incorporated the spring cushion hub from a stock MR2 clutch.
Incorporating the cushioned hub would insulate the splines for shock loads and provide a little misalignment tolerance. After the experience with the straight coupler these durability advantages, along with a provision to securely clamp the coupler to the shaft to prevent any axial movement, made the additional cost of the design justifiable.
The clutch hub was harvested from an ACT performance street clutch disc and cost about $90.
ACT Street Performance Clutch Disc
The rivets fastening the friction disk to the hub were carefully drilled out. The rivets also serve as spacers for the hub plates and can be seen at the bottom of this picture:
Dismantled Clutch Hub
Substitute spacers with the proper ID to fit the 1/4″-28 screws that replaced the rivets were easily sourced from McMaster-Carr. They can be seen between the screw and old spacer.
The yoke was machined by Robert at Artistic Machining and then sent to Form Tools to have the spline EDM’ed. A shaft collar was also incorporated into the design to nail the whole thing down.
All the parts were put together with red Loktite and installed just prior to bolting together the motor and transmission.
I had left the eMR2 in the garage last year after pushing the throttle produced clicking noises from the motor bay rather than any forward motion. I figured the noisy transmission had finally given out and embarked on the rebuild of the spare unit, something I had wanted to do in any case. I had entertained the possibility that the coupler may have been damaged but considering how sturdy it was it didn’t seem like a likely possibility.
Only last week did I finally drop the drivetrain out of the car to separate the motor from the transmission to take a closer look and it was a surprise. The transmission still rotated freely so the theory that a bearing had seized or other catastrophic internal damage occurred didn’t appear to be the problem. The pile of black powder settled at the bottom of the bellhousing did look out of the ordinary, though. The coupler had also shifted towards the transmission and I could see the mangled remains of the self-locking retaining ring pitifully dangling from the input shaft. The coupler had been laterally constrained by the end of the splines on the motor shaft and the apparently completely inadequate washer at the other. Figuring there not being much possibility of the coupler wandering, I didn’t use something more substantial like a clamp collar but more secure positioning will be incorporated inyo the new design. Examining the coupler produced the first clue; both splines had stripped completely and one of the pins had a chunk torn away. Tearing material away from a hardened pin isn’t the easiest task.
The electric motor puts out more torque than the four cylinder but considering I wasn’t hard on the car and it had only travelled about 100 miles it didn’t make sense that the splines would be completely destroyed in so short a time.
It was then that I noticed that the collar around the transmission input shaft revealed a lot more of the shaft than I remembered. Compared to the rebuilt unit there was at least half an inch missing. That’s when a closer look at the pins on the coupler revealed discoloration from high temperatures and wear on one of the pins that had slightly backed out.
Apparently the motor was working double duty as a metal lathe, grinding the coupler against the transmission collar and absorbing enough power to flatten the coupler splines. So that’s where all the power and range went.
The ground-down input shaft collar...
On the bright side, at least the destroyed splines were on the coupler rather than the motor, which would have been a far worse situation. I thought about getting the coupler hardened but this situation is a good reason not to do that. It’s much more preferable for the more easily replaceable (though still expensive) coupler to absorb the damage rather than the motor or transmission.
...and what it should look like
During the design stage a couple years ago I had also developed another coupler that incorporated the shock absorbing hub from the original clutch but went with this design based on its simplicity. Back then it didn’t seem like the spring hub was necessary as there would be no transmission shifting and the electric motor wouldn’t produce the internal combustion vibrations that the sprung hub is designed to moderate. Now it appears that retaining the sprung hub is a good idea to relieve the unhardened splines of shock loads so they can live a less stressful life. There’s additional insurance in the fact that the spring hub can absorb a little angular misalignment just in case there’s some relative motion between the motor and transmission.
I brushed off the old design and incorporating a way to constrain the coupler on the shaft so it doesn’t slide around again. The spring hub will be harvested from a sacrificial clutch disc that’s arriving within a week.
While out at DriveCurrent I gave a lunchtime presentation about the basics of EV conversions. For your entertainment (and maybe even info-tainment due to the many COLOR pictures) I’m making it available for download. To give you an idea of what it’s about, a snapshot of the table of contents is below. Click here for the pdf document.
Last week I spent a couple of days in San Diego talking to Joe and Bryan at DriveCurrent about projects we can do together. Some exciting developments came out of the meeting and will be the subject of an upcoming post, but this post is devoted to the brief respite we had from meetings to check out the fastest street legal EV available.
On the one sunny day between days of constant rain that some San Diegans had never seen before, the three of us made a trip to La Jolla to accomplish two things:
1. Have our ideas for commercializing EV conversions bashed to pieces, and
2. Get a ride in a Tesla.
The dismemberment of our business plan wasn’t what we were expecting, but at least it was mostly constructive criticism we’ll be using to make our case stronger. We see a lucrative market for conversions in quantities below the volumes that the major automakers require for them to become profitable, given their large overhead. Now we know we have to show that in our plan.
Anyway, back to the interesting part, the ride in the Tesla. Our business consigliere set us up with a friend of his that had taken delivery of Roadster #37 just a month before. As we rolled up to his garage in the hills of La Jolla he and the car were waiting for us, resplendent in dark red with contrasting black leather (the car, I mean).
Aside from all the drama surrounding the company, the Roadster is a beautiful car. The lines flow smoothly and belie the car’s size; it looks bigger in pictures than in real life. To my eye, the design is far more attractive than the Lotus Elise it’s based on. The Lotus has all sorts of bumps, strakes, wings and spoilers that scream to everyone near and far how hardcore racer it is but it comes off a little too much like little man syndrome to me. The Tesla design is much cleaner and mature, letting the basic physicality of its low stance, trim proportions, and the sparing use of functional cooling and aerodynamic features to let everyone know that it’s something special without getting all red in the face about it.
Though there are plenty of pictures of the Roadster on the net, I had to snap my own. While I worked my way around the car, Joe and Bryan were getting the guided tour by the owner. As I was shooting the front end, the three of them were gathered around the charge port. Right then I heard a “PING, whack, thunk, thunk” coming from around where Bryan was standing. The owner turned around and started asking “What happened? What was that noise? What happened?” Bryan didn’t know as all he did was open the charge door and then heard the noise. He was extremely contrite and apologetic but no one could figure out what exactly happened. Seeing the melee of the owner loudly and repeatedly asking what happened, Bryan extremely contrite and worried sick about the whole thing and Joe trying to stabilize the situation by acting as a go-between, I figured there really wasn’t anything I could contribute and decided to ignore the whole situation and keep shooting. If we were going to get thrown out now I at least wanted some proof I had been there.
It turns out the owner was not so much upset about Bryan mauling his new $100K limited edition Roadster but was more interested in what happened in a more detached, scientific sense. Bryan guessed that the part fell down the air intake right behind the charge port butsince no one could see, much less reach down there, we kind of moved on with apparently no hard feelings from the owner. Bryan, of his own accord, now maintained a safe distance from the vehicle.
Amazingly, the owner still wanted to give us a ride so I clumcily clambered over the wide sill and dropped myself into the very comfortable and low bucket seat. The wide structural sills mean the occupants literally sit shoulder to shoulder, as opposed to the MR2 where a tall and wide center tunnel gives each occupant their own personal space. I wasn’t sure what kind of demonstration I would get but the owner, who’s about 80 years old, wasted no time in flooring it through the residential streets of his neighborhood.
Several times I got to experience the full, unyielding acceleration from a standing start up to probably 65 mph. Preparing for launch in a Tesla is simple with no fancy throttle, gearshifting or clutch technique to perfect, the only requirement being a driver willing to punch it and hold on. The traction control nixes any unnecessary wheelspin, channeling all the energy from those 6831 liquid-cooled lithium cells into pure forward motion. The closest sensation is that of a jet on take-off: the whir and whine of the motor increasing in pitch as the speed piles on and the unrelentingly powerful yet smooth thrust that hurtles the car into the distance. As powerful as it is from a standing start, the owner insisted the really impressive feat was mid-range acceleration. From about 40mph on, nothing can catch it.
Joe said I had the ultimate in stupid grins as I got out of the car and I believe him. He got a little shorter ride and came away just as impressed.
While we were away, Joe and Bryan found a little metal bracket that was the cause of all the earlier commotion. The spring that held open the charge port had fractured and from the looks of it was close to breaking before Bryan ever saw it. That’s our story and we’re stickin’ to it.
The ghost of futures past
On the eve of what will be a public admission of the catastrophic financial situation Detroit’s Big 3, and especially GM, have gotten themselves into (along with how our tax dollars are *DESPERATELY NEEDED NOW* to help them), I thought a little history lesson is in order.
Over the past 40 years, the new era of the electric vehicle has been heralded with the demonstration of sleek space age cars accompanied by exuberant press releases detailing the wonders yet to come.
The closest we came last time was in the early 90’s when defense contractors like Northrop and Lockheed Martin turned their considerable talents away from building Cold War death machines to leveraging their technical expertise into more commercially viable areas. The electric vehicle was a part of that plan and, funded with government money in the form of the Partnership for a New Generation of Vehicles (PNGV), some of the EVs of that time from the Big 3 had powertrains designed by people whose talents were previously poured into spy satellites, missile systems and submarine propulsion systems.
The US industrial complexes were remaking themselves to adapt to new technologies that would make possible truly low emission transportation.
In hindsight, the apex of this era can be traced to the debut of the NiMH powered EV-1 in 1998. This press release from GM shows how little has changed in ten years.
Notice the timeline of hybrids by 2001 and fuel cell vehicles by 2004 along with the announcement of Ovonics’ NiMH batteries, a technology nearly completely buried and forgotten even though it showed the best performance and has the longest track record powering electric vehicles compared to any other advanced battery technologies. Also note the series hybrid with 40 miles all-electric range and a small gas motor (a turbine in this instance) to extend range to 350 miles (Volt anyone?).
GM also had the graciousness to acknowledge the part played by government, “which contributed to the technologies unveiled today.”
Something to keep in mind as the Big 3 come, hat in hand, looking for your money again. This time simply to keep them alive. Where’s our return from last time?
So as Martin and I were running around town shaking down the eMR2 the transmission went out.
There was a little jumpiness from the drivetrain creeping in earlier in the day but I figured it was due to the worn engine mounts. Just before drive was lost the jumpiness was particularly bad but sometimes you just have to let something break to figure out what’s wrong.
Drive was lost taking off from a stop with a little pop and a zizzing, as if a spline was stripped, yet the transmission shifted OK. None of the gears would work, simply producing the zizzing noise. It’s hard to believe the coupler failed but it’s certainly possible. The other possibilities include a stripped spline on the shafts or a catastrophic failure of the final drive.
So instead of videos of the car in action, I’ll have to entertain you with pictures of the transmission teardown when it happens in a week or two.
In other news, the bamboo/balsa frames for the velomobile came in and look beautiful but were built with the wrong thickness balsa core. Recovery options are being conjured up.
Though it came in a rather ratty looking box and none of the fasteners for the cover could be found, I scavenged enough screws to fasten the cover on the inverter and put it back into the engine compartment where it belongs. It ran a bit inconsistently at first, something I racked up to some bubbles in the coolant that triggered amp limiting due to temperature but once that was worked out it ran like I remember it-almost. I think I have to get a few cycles on the batteries to wake them up again. They were left inactive for about 6 months fully charged, but nevertheless it’s still a shock to the system that will take a few cycles to absorb.
For some reason, power wasn’t getting to the front of the car so no headlights, wipers or vacuum brake assist. In the process of disconnecting everything to diagnose the inverter problem there must be something yet to be hooked up.
Once everything’s buttoned up I’ll post some video.