Reverse Engineering

3D-Scanning

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: modernes-engineering.ch)

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

Background

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).