Reverse Engineering


I am working currently on an optimized drive kit. The basic idea is to go for a direct drive based on my experience that I am running always in the 3rd gear. As on of first action I contacted a specialized company to scan an existing gear-box-housing (company name:

The first scan created raw data in the are of 260 MByte (*.stl-file) with an accuracy of 0.02mm. The data was then reworked into a parametric model with a reasonable size of 4 MByte (*.stp-file). Such a small file can easily be handled in every CAD tool.

Why a direct drive?

There are different reasons:

  • There is no need for changing gears since an electric motor provides the max. torque from zero speed. Hence the gear changing mechanism and its pinions can be removed.
  • A direct drive (only differential) has less parts. Less parts means less noise, less weight, nearly no backlash and higher efficiency.
  • My current drive needs an oil pump to supply the input pinion with gear oil. Without the input pinion I can get rid of the oil pump.

The next steps will be to start defining the different parts to fix the electric motor on top of the gear-box and to couple it with the main axle driving the differential.
I will keep you posted about the upcoming design steps.
Cheer Erich

Homemade Type 2 Wall-Box


We bought last summer a commercially available electric car (an additional EV besides the converted E-Mini). After some discussions we have selected a BMWi3 as our family car. The i3 is really convenient to drive and easy to handle – the drawbacks are the limited range and the rather high price.
As a standard charging possibility we got 230V-cable (only) which limits the charging power to 1.9kW (single phase on a 10A socket). It takes more than 15 hours to fully charge the 30kWh battery. I decided therefore to make a homemade wall-box which allows to charge the car with a maximum power of 11kW – this reduces the charging time to 3.5 hours. Why homemade? On one hand I wanted to get familiar with the corresponding charging possibilities and on the other hand because wall-boxes are quite expensive (about 800 € – without the installation) compared to the built-in components.

Insides Type2 Charging Station
Built-in Components

The Type 2 is an European specified charging plug/process for electric vehicles (IEC 62196 Typ 2 & SAE J1772). The communication between the charging station (power capability) and vehicle is done through a simple PWM signal and connected resistors on EV and charging -station side. There is no serial bus communication involved (no CAN nor Ethernet, .. …). Small printed circuit boards (EVSE Wall-Box) doing the corresponding PWM can be bought for about 70€ in the internet with the corresponding manuals how to wire the entire box. All you need besides the small print is a suitable contactor (able to switch the max. power), a box and a charging plug with cable. I was able to make the box for about 300€.
The wall-box has a switch which allows to choose between 10A or 16A loading current. The contactor is designed to switch higher loads but the supply in my garage is for a max current of 16A (T25 Swiss socket with 3x400V and 16A which results in 11kW power level).

Different Charger Adapter Cables

Charger adapter for different socket outlets

I have made in-between different charger cables to handle all available sockets in Switzerland.

Charging Adapter Cables

The on-board charger is capable to deliver 115.2VDC with max. current of 20.5A which results in a charger output power of 2.4kW. With an efficiency of about 90% the chargers input power is in the range of 2.7kW, which requests a 16A / 230V single phase socket. I intend now to modify the charger so that I can lower the charging current (activated by a switch) in order to charge the car also on a standard 10A / 230V socket.
Further, I added some adapters to connect the charger cable to IEC 60309 16A or 32A three-phase socket,  however only one phase and the neutral wire are connected to the three-phase system. More and more Type2 sockets are now used in Switzerland on public charging stations. I bought a corresponding plug (green as shown above) and added two buttons on it to simulate the vehicle detected and vehicle ready-status to get power from Type2 stations.

Best regards Erich Butler

Drive Unit Assembly

Drive unit: Motor combined with old gearbox

Bommy (see comments) asked my to explain how I did the coupling of the old gear box with the electric motor. I added some further pictures under the tap “drive train”, which show how it was done

Basic Idea

The basic idea was to insert a new shaft in place of the old crank shaft which supports and holds the old input pinion exactly at the same position as it was before. The input pinion was then coupled with a tooth belt pulley so that the electric motor can drive the gear. Sound as it was a piece of cake – but it wasn’t!

A Challenge – hot Bearings and Input Pinion

There were several small challenges. E.g. I tried to run in a first approach the new shaft and its greased bearings and the old input pinion without active oiling. But during first runs the outcome was that the pinion and  shaft bearings got too hot due to the friction (input to 2nd pinion) and fast turning of the shaft (grease). Luckily a colleague of mine – crazy chap who restores in his spare time old Range Rovers – helped me to add an oiling system. We placed an additional oil pump which provides the bearings and the input pinion with oil. Now the drive unit runs soothly and very efficient.


I’ve seen other solutions how to couple motor and gearbox of the Mini. For instance a solution where the electric motor was directly coupled with main axle of the gear box. This is a very smart and compact design with less turning parts. It needs no additional shaft, input and 2nd pinion nor oiling system. However I do not know how the sealing of the axle was done so that no oil leaks out of the gear box. If there is someone out there, who knows how to do it, then please let me know …. ;-).

Happy New Year  …  Erich Butler

Approval for Road Use

License plate number: LU135719

Finally I managed to get the approval and the official license plate on Wednesday 13th December 2017.  I am very happy that everything went well in the second round. The chief expert tested the Electric Mini even on the motorway and reached a maximum speed of 120 km/h.

This is the link to the corresponding agency / authorities:



So far I did some test runs in Lucerne and its surrounding. I can summarize the first impressions and outcomes as follows:

Consumtion0.14 kWh/km
Range (calculated with consumption and battery capacity)73 km
Acceleration / SpeedNo problem to follow traffic
Problems1.) Voltage drop during heavy acceleration in 3rd gear. Converter starts to limit.
2. ) Battery pack needs to be better balanced

Keep you posted ….. take care …. Erich Butler

Final Acceptance

Waiting ……

On the 6th December 2017 the time finally came and we (the garage owner helping me with the mechanics and I) showed the Mini to the authorities. After a two hours inspection by the  chief expert himself we got a tentative OK for the use of public roads.
There was only a minor issue with the hand brake and that’s why we have to show the car again this Wednesday. I hope that everything goes well I can drive home with the Mini with the official vehicle’s registration plate.


Start of acceptance tests

I have to admit that the Department of Transportation of the Canton Lucerne was very open and supportive. This helped a lot to get the approval.

Keep you posted …. cheers Erich

Ready for the official Acceptance by the Authorities

I have not written for a longer time. I was absorbed with some family affairs and hobby priority #1 was to finish the car. Now the car is almost ready for the official acceptance by the authorities of the Kanton Luzern in Switzerland. I sent them a report with all technical details and got a first feedback (some remarks), but overall the green light to show the car the in the upcoming weeks. Keep you posted ….. cheers Erich