Metadyne
![Spare Metadyne carbon brushes. They are individually wrapped and, together with labels, sealed in plastic. Total length including the connecting wire and ring is 115 mm. The thickness of the carbon slab is 8 mm.](/Images/godic/202501/27/Spare_Carbon_Brushes_for_a_Metadyne_machine3452.jpg")
![Three arrangements of a metadyne cross-field DC machine, and the construction of Macfarlane's Magnicon](/Images/godic/202501/27/Metadyne3452.jpg")
![A London Underground CP train (in red) at Upminster. They were originally fitted with Metadyne controls and were the first electric multiple units to use regenerative braking.](/Images/godic/202501/27/CP_&_R_at_Upminster3453.jpg")
A metadyne is a direct current electrical machine with two pairs of brushes. It can be used as an amplifier or rotary transformer. It is similar to a third brush dynamo but has additional regulator or "variator" windings. It is also similar to an amplidyne except that the latter has a compensating winding which fully counteracts the effect of the flux produced by the load current. The technical description is "a cross-field direct current machine designed to utilize armature reaction". A metadyne can convert a constant-voltage input into a constant-current, variable-voltage output.