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From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
Translated letter from an Austrian engineer detailing modifications to a dynamo to prevent sparking.

Identifier  ExFiles\Box 57\2\  Scan131
Date  17th August 1928
  
Copy of translation of
Letter from Rudolf Mir, Engineer, of Graz (Austria)

August 17th 1928.

Dear Sirs,

I have had an opportunity of examining and repairing an electric installation of your manufacture. You will probably be interested in hearing that I have altered the construction of the dynamo in this, that I made slight alteration to the hindward horn of the pole shoe. The machine - which by a high number of revolutions always shewed strong formation of sparks, because the rotation of the neutral zone above 2000 r.p.m., considered in the direction of rotation, caused the edge of the pole shoe on the hindward horn to be much too much induced magnetically - works now very well indeed. Even in the case of greatly undersized collector, the formation of sparks at any number of revolutions is practically avoided. Because you utilise in your system, current regulation instead of tension regulation as in the "Bosch" and "Scintila" there must be an accurately calculated and experimentally found curve for the hindward horn of the edge of the pole shoe. The pole shoes must not, as it were, press close (cling to) the rotor periphery, but must be planed (? flattened) This is what I did in the above case; I made slots in the edges of the pole shoe on the hindward side, as shewn in the figure. The success was astonishing. Your machine, which -in your interest- will with this small alteration becomes really a first-class machine, should certainly deserve a little closer attention. I am quite willing, at your request, to communicate to you the results of my experiments. It is a pity that your electric installation does not enjoy the reputation it really deserves. I wish to tell you quite frankly that I have been surprised most agreeably at the other qualities of your machine. You will therefore also understand that it is only in your own interest that I am taking the liberty of communicating to you the alterations I have brought in the construction of the apparatus. The type of machine is that of a 20 HP, 62 HN.{F. C. Honeyman - Retail orders} (62.H.H)

Yours faithfully,

Top: Slotted pole shoe edge
Middle: Direction of rotation
Bottom: Perspective view
  
  


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