"Optimized rotor" by Rennschmiede Pforzheim e. V. under CC-BY-SA 4.0 DEED. And the same applies to this rotor: at the end of the product's life, the permanent magnets can be reused - without having to recycle them at the material level.

Rennschmiede Pforzheim e. V. is an association supported by students at Pforzheim University. The aim of the association is to develop racing cars in the Formula Student (FS) competition. In close cooperation with two Pforzheim companies, several generations of students from the racing forge have developed their own e-traction machine, which is characterized above all by an innovative lightweight water jacket cooling system and a modified electro-magneto-mechanical design compared to series machines.The possibility of being able to reuse permanent magnets relatively easily at the end of the product's life - i.e. without any recycling - which was already available for the original series machines, is also available for Rennschmiede's e-traction machines. The fact that the re-use approach for permanent magnets also has other advantages is described in this article.

During preparations for the 2023 racing season, problems arose when removing and reinstalling the rotors. A rotor presumably struck mechanically on or in the stator, but only in such a way that there was no visually recognizable damage to the rotor. During a later test of one of the e-traction machines on a test bench developed by Rennschmiede, considerable damage occurred after 10 minutes of the machine running idle and therefore unloaded at a speed of n =5000 min-¹. The damage pattern: approx. 1/3 of the permanent magnets installed on the rotor surface were "pulverized", only approx. 2/3 of the permanent magnets were still intact.

Real-life laboratory experiment 1: Partial repair by replacing the permanent magnets

The classic repair approach would be to replace the rotor completely. However, this would not have been necessary for the rotors of the Rennschmiede Pforzheim e. V. e-machine. Because of the "Design to Re-Use the Permanent Magnets", the rotor could have been repaired quite easily. Only the remaining partial glass fibre bandaging would have had to be removed, after which the rotor would have had to be placed in an oven so that the remaining permanent magnets could be demagnetized and the adhesive between the remaining permanent magnets and the rotor iron could be dissolved. The demagnetized and no longer glued residual permanent magnets could then have been removed, as could the powder from the destroyed, pulverized permanent magnets. And since the rotor iron was not damaged, the rotor could have been reused without any further reworking.

Real-life laboratory experiment 2: Development of a new, lighter rotor

The subjunctive mood is used throughout the description of real-life laboratory experiment 1. This is because the students at Rennschmiede "used" the damage to make an already planned change to the rotor. Even before the damage, the plan was to replace the rotor from the 2022 race year with a new one. The most important features of this new rotor are (a) The rotor laminated core is no longer a solid core, but a hollow core, which is significantly lighter as a result; (b) The rotor shaft has been shortened so that the shaft is also lighter and also results in the axial length between the gearbox and rotor being shorter and the drive being more compact.

This newly designed rotor was manufactured. Thanks to the unchanged principle of "Design to Re-Use the Permanent Magnets" and the excellent craftsmanship of the Pforzheim-based company, the permanent magnets could be glued on by students at Rennschmiede themselves. Bandaging the permanent magnets was also no problem. Ultimately, Rennschmiede was able to use an optimized, shorter and lighter rotor in the e-traction machines for the 2023 racing year.