The Wrenn brothers were granted patents on their Formula 152 range. The first being 844.436 which was quoted in the February 1961 Price List with ‘others pending’.

The November 1962 Price List also listed 894.837 with still ‘others pending’. By the time of one of the last Catalogues (possibly the last one) 894.838 had also been added. Overseas Patents were stated as pending on the first Price List and not mentioned again on subsequent Price Lists although later Price Lists from November 1962 did state ‘other Patents pending’.

When Wrenn introduced the new DC motors in 1964, and latterly the 9-volt motors in 1968, they also protected their designs with successful Patent applications, 974.830 and 1.114.543, although there was no reference to these in any of the current literature or Price Lists.

The actual Patents are available to view on the Espacenet website so I have downloaded the information and drawings for each of them below. Since the Patents are only granted for 20 years, they are now obviously out of date but also in the public domain.

Abstract of GB 844436 (A)

Electrically propelled toy vehicles. Jan. 19, 1959, No. 1863/59. Class 132(3). [Also in Group XXXV]


An electrically propelled toy vehicle, e.g. a scale model racing car, comprises a body 26 mounted on a chassis 11 of magnetic material, e.g. soft iron, which carries an electromagnet coil 12 and a hinged armature 24.

This operates a spring loaded pawl 17 which in turn engages a ratchet wheel 18.

The ratchet wheel may be of hard steel or plastic, e.g. nylon, and is secured to a shaft 19 journalled in the frame and carrying road wheels 29.

A further shaft 27 carrying road wheels 28 is journalled either in the chassis as shown or in the frame.

Make and break contacts 22 operated by a projection 24 on the armature are disposed on top of the coil, and current is taken from a prepared track having two conducting strips by two collector shoes 30. In an alternative arrangement (not shown), for A.C. operation only, the make and break contacts are dispensed with and the armature consists of a tuned reed resiliently mounted.

Abstract of GB 844437 (A)

Miniature-vehicle tracks.


Sept. 17, 1959 [July 28, 1959], No. 25865/59.

Classes 132(2) and 132(3) A miniature-vehicle diverting device is such that it will divert an electrically powered vehicle by engaging a guide member or members on each vehicle with a member in a vehicle guiding slot to lift the guide member or members from the slot and to divert the vehicle from one lane of a track so that it will run under its own momentum to an adjacent lane.

Each lane has a guide slot, e.g. 25, Fig. 1, engageable by one or more downwardly projecting guide members from a vehicle and also has electrically conductive strips 28 to 31 inserted in it engageable by current collectors.

Each vehicle has a pair of current collectors, the collectors of different vehicles on the same lane engaging different pairs of conductors so that, by controlling the current supply to the strips, the speed of the different vehicles can be independently controlled. Figs. 3 and 4 show an insert frictionally fitted in a guide slot, the insert comprising an upwardly sloping face 47 and a laterally slanting face 49. As a vehicle travels along the lane its guide member is raised out of the lane slot by the face 47 and is deflected sideways by the face 49.

Thus the vehicle is deflected from its lane to an adjacent lane where its guide member drops into a guide slot and its collectors make contact with the conductors. Fig. 6 shows an alternative embodiment where a similarly shaped deflector is pivoted at 51 and is operated through a cranked spindle 55 by a lever, Bowden cable or solenoid.

Vehicles may be raced by controlling the diverting devices and current to the strips, the vehicles overtaking each other by changing from one track to another and back again. According to the Provisional Specification, instead of a guide slot, a raised guide rail having conductor strips incorporated in it or a pair of guide grooves for miniature-car wheels may be used.

The Provisional Specification also describes overhead wires for miniature trolley buses or trams and points similar to those used in model railway tracks. Specification 844,436 is referred to.

Abstract of GB 8944838 (A)

Miniature vehicle tracks.


Jan. 20, 1960, No 2068/60. Class 132(3)

A miniature rail track assembly comprises a flat base member 1 having linear recesses 7 in its upper surface, inverted channel section rails 3 to 6 inserted in the recesses, and holes 10 drilled in the base member upwards meeting the recesses, the side flanges of the rails having been splayed into the holes by a swaging tool 11 to hold the rails in position.

The rails may be electrical conductors, miniature road vehicles such as disclosed in Specification 894,837 each having collectors to pick up current from a selected pair of rails. As shown, the track has channels 2 which are engaged by projections from the vehicles.

Track sections are joined by projecting pieces 13 each of which may be a short length of inverted channel of smaller gauge than a rail so that it can be pushed within a rail channel. These pieces 13 may be splayed in position simultaneously with the splaying of the rails.

Rails are splayed in position while the base 1 is inverted on an anvil surface.

To provide rails flush with the track surface a flat anvil is used, to provide sunk rails the base when inverted is meshed with a ribbed anvil, and to fit rails which project from the track, so that they may receive flanged wheels, a grooved anvil is used to receive the projecting rail tops.

The track assembly may be made from a moulded or extruded synthetic plastics substance, may be formed in complete circles or ovals, and may comprise more than one track.

Abstract Of GB 974830 (A)

Improvements in electric motors.

Abstract Of GB 974830 (A)

974,830. Electric motors. G. & R. WRENN Ltd. May 13, 1963, No. 18824/63.

Heading H2A. A small D.C. motor has a permanent magnet rotor 53 and a wound stator having a plurality of windings 45-50 with one end of each winding connected to a brush which co-operates with a two-segment commutator 14, the other ends of the windings being connected together, so that a rotating magnetic field is produced.

As shown, T-shaped pole pieces 44 are located by moulded nylon end plates 54, 55 which also act as the shaft bearings, the poles are machine wound with three coils 45-46, 47-48, 49-50, and enclosed by hexagonal yoke 57. A third nylon moulding is located in the yoke and used as the brush holder and outboard bearing support for the commutator assembly. Commutator 14 is built up by forming steps on two pieces of shaft and after inserting insulation 82 (epoxy resin) between them, reassembling the segments 80, 81 and when the insulating resin has set grinding the shaft to the required diameter. Holes 60-62 bored in the moulding act as holders for the carbon brushes 63-65 and pins 66-68 support springs 71 which are anchored in the moulding at 74 and apply pressure to the brushes. In order to replace the commutator, contact plate 84 can be removed by releasing spring 91 and the commutator withdrawn from tongue and slot coupling 78.

Connection between the two segments and the resulting short circuit to the supply due to the brush being wider than the insulation between segments is prevented by designing the commutator to run eccentrically so that the bush face remains relatively flat, Fig. 2 (not shown). In operation tags 89, 92 are connected to the supply and current passes via the motor shaft to the commutator and hence in sequence to the stator windings to produce a rotating magnetic field, Figs. 3-8 (not shown)

Abstract Of GB 1114543 (A)

Improvements in miniature electric motors.

Abstract Of GB 1114543 (A)

1,114,543. Electric motors. G. & R. WRENN Ltd. 31 Aug., 1966 [15 Oct., 1965], No. 43782/65.

Heading H2A.
A miniature motor has an air-core field coil 18 whose
sides are in the same plane as the axis of the permanently magnetized rotor 17.

The motor shaft carries an interrupter cam 37 and the coil ends are cranked to lie
on the bearing pedestals 15. The base 11 is of plastic