OwnerJay Dee
LocationTorrance, California US map
WebWebPage
Vehicle1970 Myers Motors B.F. Myers
.
This is a 1970 B.F. Myers "Towdster" Dune Buggy.
Bruce designed its predecessor, the "Tow'd", to
be light enough to be towed behind a car for
offroad fun in the desert. A tow bar slid out
of the steering column support when needed.

Instead of the shortened VW chassis under a
fiberglass body that is the basis for most Dune
Buggies, Bruce saved weight by integrating seats
and a trunk into a fiberglass body, which rests
on a steel hoop that connects the front end and
the rear transaxle.

However, when it turned out that people wanted
to drive it to the desert instead, he made the
"Towdster". This had lights and fenders that
made it street legal, but could be quickly
removed for offroad fun. It was the lightest
street-legal donor I was able to find after a
few years of searching.

This one has a VW beetle transaxle in the rear
with drum brakes and IRS (Independent Rear
Suspension, vs swing axle), and a Karmann Ghia
front end with disk brakes. There are lots of
pictures and videos on this build thread:

==> https://endless-
sphere.com/forums/viewtopic.php?f=34&t=50717

Walkaround Video on YouTube shot in 4k:
==> https://youtu.be/ttluo4MIt0Q

Test drive at the beach video on youtube, starts
with some vid of the rear wheel and then GoPro
off the passenger side:
==> https://youtu.be/46_EDW2tI98

.
MotorAdvanced DC FB1-4001a Series Wound DC
.
Standard 9" motor with a tailshaft
.

Drivetrain4-Speed VW transaxle, CANEV Adaptor plate, rear
motor (9" ADC FB1-4001a)
ControllerCafe Electric Zilla Z2K-LV
.
The controller's 2,000a max output is overkill
for this build, and way more amps than a single
9" motor can use, but I got it a good price. I
have since bought a more appropriate Z1K-HV to
replace it, but I haven't gotten around to
swapping it in yet. I upgraded the hairball to
one with -A and -P options, and I find the Prius
hall-effect pedal is much smoother than the PB-6
throttle it replaced.

All the cables in the power circuit are 4/0. In
addition to the (+) side EV200 contactor managed
by the Zilla, I have a (-) side EV200 contactor
activated by a dash switch.
.
Batteries42 A123 Systems APM20 cells in series, 3 parallel cells each, 3.65 Volt, Lithium Iron Phosphate
.
The pack is made of three a123 factory-made
modules: one large 28s3p module (106lbs) and two
7s3p modules (30lb each). Because of a123's low
resistance, it has very little Peukert-Effect
sag under load. The low resistance also allows
for a 30c discharge, so this pack could could
theoretically put out 1,800a. The Zilla Z2K is
up to that duty cycle, but it far exceeds what
the motor and chassis could handle.

I pulled 7,532wh from the pack on the only full-
discharge test I have done so far, 57.19ah until
the lowest cell hit a conservative 2.7v limit.
Pretty good for a pack rated at 58.5ah, I
expected to hit 2.7v at an 80% DOD not almost
100%. No BMS, but I have an array of (6)
CellLogs that present a bar-graph display of
each cell's voltage, and provide a cell-level
low voltage alarm.

I designed a battery box in sketchup to fit the
area behind the seats where the gas tank used to
be, and paid a metal shop to weld it from
aluminum 6061 sheet. It has a slow blow fuse in
the middle of the pack, and silicon fuses on
both the positive and negative terminals. The
entire pack weighs only 219lbs, including cell
modules, battery box, 4/0 cabling, fuses, and
all mounting hardware.
.
System Voltage154 Volts
ChargerVicor Megapack PSU
.
I bulk charge with a Vicor Megapack that has (3)
48v/4.2a cards in it configured to 150v+.
Thanks to the quality of a123's LiFePO4
chemistry, the pack stays pretty well balanced,
but periodically I follow a bulk charge with a
top balance using an array of Voltphreaks 2a
Single-Cell chargers.
.
HeaterSunny Los Angeles beach weather!
DC/DC Converter
.
To avoid the added complexity and high fail rate
of of a DC-DC converters, I power the 12v
systems with a 4s1p pack of 10ah Headway LifePO4
cells instead. I have a 4s1p pack of a123
19.5ah AMP20 cells to replace the Headways when
I get back to working on this project.
.
Instrumentation.
A Grin Technologies (thanks Justin!)
Cycleanalyst V3 in a 3D printed enclosure do
columb counting and display volts/amps/KW and
much more. (6) CellLogs in a 3D printed
enclosure monitor the pack. Remote LEDs from
the hairball in the dash. Everything else is
stock VW.
.
Top Speed75 MPH (120 KPH)
.
Top end is limited by chassis, and not power - a
lightweight dune buggy is made for off-road, not
high speed. When it had a gas engine it was
manageable at 75mph, and it has MUCH more power
now.
.
Acceleration.
Stunning, like nothing I have felt before.
Since this only weighs about 1,000lbs, at full
amps the power-to-weight ratio is similar to
that of the 3,500lb 2015 Corvette Z06 - not that
the chassis could make as elegant use of the
power. While rolling along in 2nd gear I can
break the tires loose with a tap of the
throttle.

However, after about a dozen or so of these
rolling burnouts, the clutch started slipping.
Replacing it with a KEP (Kennedy Engineered
Products) stage 1 pressure plate (180lb/ft) and
clutch did not help. I think I broke something
in the transaxle since the onset of the problem
was sudden. Maybe under heavy load, the pinion
shifts and the tranny binds up a little?

It still pulls pretty hard under a gentler
throttle, but I can't do the wild stuff again
until I sort this out.
.
Range25 Miles (40 Kilometers)
.
I got 24.9 miles in my real-world max
discharge/range test, which included lots of
stops, steep hills, and hard launches. I only
need 16 miles for my daily commute, less for
beach rides when I retire, so this more than
meets my needs. However, I would like to get at
least 35 miles from this to prove out my
original Design Criteria.

Under Rickard's 100whm/1,000lbs theory, I should
get a 75 mile range from the 7.5kw that the pack
supplies. That probably exceeds reality, but I
think by servicing mechanicals I can get a
better wh/m.
.
Watt Hours/Mile303 Wh/Mile
.
I think the WHM consumption is pretty high for
such a light vehicle. Maybe I have a frame leak
in the motor (which was used for years in my VW
Bus Conversion). Maybe the transaxle problem I
am pondering is wasting power. I haven't
checked the wheel bearings yet, they probably
need service and are consequently wasting power.
All things to look at when I get over being
burned out on this project again.
.
Seating Capacity.
2 people and a trunk.
.
Curb Weight1,035 Pounds (470 Kilograms)
.
I have not had this formally weighed this yet.

While researching the donor, I got a lot of data
points saying that a gas powered tow'd weighed
1,000lbs, so I use this as my basis. I have
carefully weighed everything I've removed and
added to the car during the conversion, and
about 35lbs more went in than came out. In the
process, I shifted about 100lbs from behind the
rear axle to well in front of the rear axle,
improving weight distribution.

I chose a Towdster because I was specifically
looking for the lightest freeway-legal donor
vehicle I could find. For comparison, the data
points I was finding indicated that typical dune
buggy on a VW chassis weighs about 1,300lbs, and
the VW Beetle weighs 1,760-1,850lbs.
.
Tires4
Conversion Time.
I bought this in May of 2013.

I finished it the first time in September of
2014, but the 500a Kelly Controller I used would
only supply 88a so it accelerated like a golf
cart, leading to my most significant burnout on
the project.

In July 2015 I started Phase II - the Zilla Z2K
upgrade and a bunch of improvements. Phase II
was completed when I did my full-discharge test
in December 2015.

As typical, I had to do a lot of restoration
along the way that significantly added to the
timeline. Despite the previous owner's
assertions to the contrary, the build was pretty
tired when I got it, almost every system needed
reconditioning. It was extremely dirty too, but
now you could eat off the tranny if that is your
thing. I also completely rewired the entire car
from scratch and designed the layout/harness
myself. I learned a whole lot about VWs along
the way, which added significantly to the
enjoyment side of the equation.

I had a few periods when I was burned out from
working on it every night/weekend/vacation, and
I had to forget about the project in order to
regain interest in working on it. Right now I
am burned out on it again - it is hard to take a
running EV and break it down into a pile of
parts in my garage, not to mention going back to
having a huge project hanging over my head.

For now I am just enjoying it as is. It is
pretty functional, but there is still a lot I
would like to do with it, so I don't know that
it will ever be finished.
.
Conversion Cost.
A Breakdown of major expenses:

The donor cost $6k, and $600 to ship down to me.
Dune buggies can be had for less than half that,
but this one streamlined my project because it
was already registered for the street, had front
disc brakes, and rear IRS suspension.

The motor and a123 pack and Kelly controller
were from my VW bus conversion, so they could be
considered used but in the total I base their
cost on the price I paid for them.

I bought a few Zillas along the way, cheap on
eBay, and had them fixed at Manzanita Micro.

I paid to have the battery box welded for me,
but if time wasn't an issue I could have saved
money by doing it myself. I also paid to have a
controller mounting plate water jetted which was
more of a vanity than necessity.

All told, I think I am into it for about 15k
after factoring in samples, incidentals, tools,
and dead ends, but the education I got along the
way is worth more than that to me - and wow did
it expand my design vocabulary and understanding
of materials. With what I know now, and a
cheaper donor, I could do this for under 10k.
.
Additional Features.
Too many to mention. Lots of pictures and details on this build thread:

==> https://endless-sphere.com/forums/viewtopic.php?f=34&t=50717
.


.
I wanted to demonstrate that by designing for a 35 mile range, an EV
could better leverage the benefits of the electric drivetrain, making
it extremely light to be as fast and agile as a supercar, yet
economical to build and run, non-polluting and low maintenance.

I am one of the 60% of Americans who travel less than 30 miles per
day. With all the hype about range anxiety, car manufacturers are
building EVs with ever larger, heavier, and more expensive packs, in
turn requiring heavier chassis, bigger motors, and more complex
systems. I think we lose many of the advantages of a simple electric
drivetrain when we build EVs to service the duty cycle of gasoline
car. I'm not knocking Tesla - Elon Musk is my hero and a model S or
X is in my post-retirement future - I'm pointing out that Tesla's are
more car than much of America wants to pay for.

I think there are some great options out there for those of us who
appreciate the benefits of an EV. However, I can understand the
uninitiated not wanting to pay $30k for an EV that only does 100
miles and looks/handles/accelerates like a low end car... But they
WOULD pay $10k for an EV that performs like a supercar even if it
only does 35 miles.

If I can build such an example for 10k, surely Big Auto can do it
cheaper wholesale and make a profit. I think there is an untapped
niche market there, but servicing it would be a parasitic drain on
the sales and service of more expensive vehicles, so Big Auto is
unlikely to do so.

NEVs are a step in the right direction, but hampered by 25-35mph
speed limits and heavy lead-acid batteries. For example, 98% of my
commute to work is on 25mph-35mph suburban streets, but the entrance
to my company is on a 45mph road so I can't get there in an NEV.

Although I paid a lot for a "classic car" donor so my message
wouldn't get lost in the looks, anyone with appropriate skills could
do a similar build for less than $10k, using a $2.5k generic dune
buggy, a used motor/controller for $3k-$4k, and part of an a123
battery pack from a wrecked Chevy Spark for $3k. As I got into dune
buggies, I discovered that there is a huge garage-built culture out
there, father/son teams and serial hobbyists building buggy after
buggy, so I hope a few of them give an EV build a try!
.



code by jerry