Gilbert D.C. Motor

© Brooke Clarke 2007

Joshph Henry published the idea making a tight winding of insulated wire to form electromagnets.  William Sturgen combined that with a Commutator to make a rotary DC electric motor.  He made a two pole motor that needs a manual spin to get started.  By using three poles the motor is self starting.  Sturgen's electromagnet used bare wire and so had a small number of turns and required high currents.  It would not allow things like a telegraph since the transmission wires would be too big and expensive.  The electromagnet by Henry ran from a much lower current and that allowed it to work at longer distances using practical wire sizes.  DC motors are one of the logical follow on developments once you have an electro-magnet.

This is a three pole DC electric motor.  Gilbert called it the P58.  It was used in Erector Sets made between 1914 and 1936.  The magnetic field the armature works in is provided by a filed coil instead of a permanent magnet.  The field coil and the Commutator brushes are both brought out to thumb nuts.  This allows for a number of experiments both in terms of changing the motors direction of rotation and in terms of driving the them from seperate power supplies to see the effect of each.  See the Links section below for a method of characterizing a DC motor.

In the above photos you can see that the front and back sheet metal parts are identical although the front and back sides make use of different holes.  It's usually less costly to make twice the quantity of one part than half that quantity of two parts.  Note the cost savings does not stop at the manufacturing operation for the part but continues to storage, documentation, inspection, etc.

The mounting holes are on a 2" square pattern and will clear number 8 screws.  This matches the hole pattern in the Erector Set parts.  The base can contain either a direction reversing switch or a switch that includes a slow speed position by switching in a resistor.  The first patent filing date is in the 1916 time frame and as late as 1923 this motor was being designed into new Erector Set toys.

This motor uses cylindrical metal screen brushes which is a more advanced method than the sheet metal brushes that were used on the early DC motors like on the Electro-magnetic Toy engine and Weeden motor but not as advanced as carbon (Graphite) brushes.

Problem As received the motor is non operational.  The problem is somewhere in the armature where there's an open circuit on two of the pole coils, only one has continuity.  This should be a straight forward repair, but we'll see since I've never done it before.  Here's a photo after separating the armature from the field.  The above photos are from eBay.


The field coil and electrical steel laminations can be seen at the left along with the brushes.  The four terminals and thumb screws are below the left image.

On the right is the armature.  On the frame facing the armature there's a circular mark about 0.35" diameter like a washer had been sitting or turning there.  The pulley is a press fit on the shaft.  The Commutator  assembly is pressed onto the shaft which has serration's to keep it form rotating.

With three coils there are six wire ends.  The Commutator has three sections.  There are two ways to wire the coils to the Commutator.  One way would be to run the two wires from a coil to adjacent Commutator segments which would result in two wires going to each segment.  But this motor has only one wire going to each segment.  The other way would be to connect one wire from each coil to a common point and bring out only three wires.  This causes two poles to be energized in series when adjacent segments are under brushes.

Using a sewing needle in a pin vise the cloth at the back of the armature was picked away revealing the three wires soldered together.  Measuring the resistance from the common point to each of the commutator segments showed which coil was open and the other two were OK.  A scale drawing was made of the armature and in particular the area were the coil is located.  This made clear the direction of winding and where the start and end points were.

If a splice was made there would be a big bump and also then the wire would be too short or there would be fewer turns so a new 24 AWG wire was wound.

The wire was unsoldered from the commutator.  At this point the resistance was double checked to make sure that the problem was not in that joint and to make sure this was the correct winding.   After a couple of feet the wire was open.  Then the rest of the wire was unwound.  Rather than disturb the existing solder joint the old wire was cut off.   A length of 24 AWG was cut from the spool by threading it and the old wire side by side using both pieces of old wire and then adding 12 more inches.  After using a file to get the insulation off the new wire it was soldered to the common point and wound back onto armature.  This was done under a stereo zoom microscope to keep the turns packed tight.  There may be a few more turns since when the coil got the the ending point there was only 6 inches of wire left.  it was cut to the proper length, a few turns unwound so it could be stripped, then rewound and soldered to the armature.

An interesting discovery is that the brushes are not carbon rods as were expected, but rather a tight roll of very fine brass screen.  Because of some slop between these rather short rolls of screen and the tubes that are the brush holders the brushes are better behaved when the motor turns one way than another, so the polarity of the DC was adjusted for that direction.

The Red and Black wires are each 14 AWG super flex and have ring tongue terminals crimped on each end.  They have extremely low resistance which I've learned is appropriate when working with this vintage electro-magnetic motors and No. 6 Dry Cells.

or play it here:

Gilbert Erector Set Switch Base Top	Gilbert Erector Set Switch Base Bottom

The red parts are fiber insulating material sometimes called Fish Paper.  It was also used in the motor as an insulator.

The Gilbert motor uses a roll of wire screen, maybe brass or copper and the movable element (brush).  The Motor Kits use bronze wire as the brush. The small motor below, the 10-100 Demonstration Motor Generator and the Weeden  use what's probably bronze sheet metal.  Modern motors use a brush that's made from a blend graphite and copper.  By controlling the resistance the brush provides some spark suppression.

The Gilbert motor has the armature wired in a "Y" so that only one coil is in the circuit at a time.  The same is true of the Electro-magnetic Toy Engine and Weeden.  So when the power is removed from a coil there's a large voltage spike generated and sparking. 

The small motor below has the armature coils connected in a delta wiring.  So the full DC voltage is across one coil and also across two other coils in series.  When the commutator changes the voltage spike that would have been large is snubbed by the other coils.  These motors only have 2 commutator contacts but other DC motors may have numerous contacts and numerous coils.  How the coils are wired to the armature contacts is a very complex subject.

In general G.E. which is related to Edison and DC motors and generators has most of the patents relating to DC rotating machines and Westinghouse which is related to Tesla has most of the AC motor and generator patents.

1066809 Toy Construction Blocks, Alfred C. Gilbert (Mysto Mfg Co), Jul 8 1913, 446/112 ; 446/113; 446/124 - the basic beam with flanges
1261019 Toy Building Element, Alfred C. Gilbert (A. C. Gilbert Co), Apr 2, 1918, 403/108 ; 403/109.5 - beam with angled flanges
1230887 Toy Building Construction, Alfred C. Gilbert (A. C. Gilbert Co), Jun 26 1917, 446/108 - roof construction
1232463 Toy Building Construction, Alfred C. Gilbert (A. C. Gilbert Co), Jul 3 1917, 52/634 - box girder or I-beam members have flanges at 90 degrees
1351565 Toy Submarine, Alfred C. Gilbert (A. C. Gilbert Co), Aug 31, 1920, 446/165 -
1492597 Toy Vehicle, Alfred C. Gilbert (A. C. Gilbert Co), May 6 1924, 280/248 - 4 wheel children's riding metal toy propelled by pumping a lever to and fro, but how to steer it?
1677281 Electric Heater, Alfred C. Gilbert (A. C. Gilbert Co), Jul 17 1928, 392/429 ; 219/481; 219/536; 219/538 - parabolic reflector type
1724470 Construction Toy, Alfred C. Gilbert (A. C. Gilbert Co), Aug 13 1929,446/96 ; 104/DIG.1; 123/41.1; 238/10E; 238/10R; 446/112; D21/495 - made from Erector Set parts
1763302 Construction Toy, Alfred C. Gilbert (A. C. Gilbert Co), Jun 10 1930, 446/90 ; 446/113 -
1815708 Construction Toy, Alfred C. Gilbert (A. C. Gilbert Co), Jul 21 1931, 446/90 ; 446/113; 446/93; D21/542 - boat shape made from Erector Set parts
1820660 Toy Building Construction, Alfred C. Gilbert (A. C. Gilbert Co), Aug 25 1931, 52/731.2 ; 446/113; 52/634 - an "L" shaped girder allows making box beam
1860835 Hoisting Apparatus, Alfred C. Gilbert (A. C. Gilbert Co), May 31, 1932, 254/330 ; 192/18R; 254/350 - P56-G AC motor operates two cable drums

1218076 Commutator, Alfred C. Gilbert (A. C. Gilbert Co), March 6, 1917 310/236- How the three brass segments are attached to the fish paper disks.
1219452, Toy Motor Installation,  Alfred C. Gilbert (A. C. Gilbert Co), March 20, 1917, 74/414- Combines this motor with control switch and gearbox.
1307094 Electric Switch, Alfred C. Gilbert (A. C. Gilbert Co), June 17, 1919 200/11G ; 200/1V; 310/68A- Connects a battery to the motor and filed coil in either polarity or off.  The motor can sit on top of the switch, like in patent 1219452 or the switch can be separated from the motor to provide a remote control.
1310613 Toy Gun, Alfred C. Gilbert (A. C. Gilbert Co), Jul 22, 1919, 124/29 ; 124/39; 124/49 - hand cranked fires two magazine fed rounds by action of spring.
Electric Switch Alfred C. Gilbert (A. C. Gilbert Co),
1323045 Toy Electric Motor, Alfred C. Gilbert (A. C. Gilbert Co), Nov 25, 1919 [filed April 18 1916] -
D58904 Electric Motor Casing, Alfred C. Gilbert (A. C. Gilbert Co), Sep 6 1921, D13/112 - two sheet metal cups jouned at the open faces, closed design.
1381985 Electric Motor, Alfred C. Gilbert (A. C. Gilbert Co), Jun 21, 1921, 310/91 - closed type for mixer, blender, fan has to do with base and mounting
1381986 Electric Motor, Alfred C. Gilbert (A. C. Gilbert Co), Jun 21, 1921,248/660 ; 310/66 - flexible mounting arrangements
1424720 Electric Switch, Alfred C. Gilbert (A. C. Gilbert Co), Aug 1 1922 [filed Nov 26 1917] 310/1 ; 105/49; 310/68A- a different way to make the switch in patent 1307094 using a cylinder like a commutator.
1445678 Rheostat, Alfred C. Gilbert (A. C. Gilbert Co), Feb 20 1923 [Filed Jan 28 1918] 338/215 ; 338/200; 338/234- This is for a fan and is just a power resistor that gets switched in to cut the motor speed in half.
1476708 Electric Motor, Alfred C. Gilbert (A. C. Gilbert Co), Dec 11, 1923, 476/64 ; 248/667 - motor tilt base for driving sewing maching flywheel
1523764 Electric Motor, Alfred C. Gilbert (A. C. Gilbert Co), Jan 20, 1925, 310/40R, - motor casing is made from two sheet metal cups that are bolted together
1526333 Toy Gear Box, Alfred C. Gilbert (A. C. Gilbert Co), Feb 17 1925, 74/397 - bolts in front of and behind the Gilbert DC motor
1832456 Electric Motor, Alfred C. Gilbert (A. C. Gilbert Co), Nov 17 1931,  310/236 - Commutator for small AC/DC motor. dia is > than armature
1832457 Vacuum Cleaner, Alfred C. Gilbert (A. C. Gilbert Co),Nov 17 1931, 15/323 ; 15/400; 15/422; 15/DIG.10; 383/40; 417/423.2 - "Kirby" type fan on motor shaft
1863320 Toy, E. N. Anketell, June 14, 1932 178/47- a crane that uses this toy motor
1914888 Fruit Juice Extractor, Alfred C. Gilbert (A. C. Gilbert Co), Jun 20, 1933, 99/501 - uses the 1832456 electric motor
1918695 Vacuum Cleaner Motor, Alfred C. Gilbert (A. C. Gilbert Co), Jul 18 1933, 310/89 ; 15/413; 310/258; 417/423.2 - combined motor and fan frame also cools motor
1926441 Electric Motor, Alfred C. Gilbert (A. C. Gilbert Co),  Sep 12 1933, 310/40R ; 310/239 - 
2027036 Kitchen Utility Device, Alfred C. Gilbert (A. C. Gilbert Co), Jan 7, 1936, 366/201 - mixer with optional juicer that fits on top, bowl sits on lazy susan off center beaters
2030201 Toy Locomotive, Alfred C. Gilbert (A. C. Gilbert Co), Feb 11 1936 105/37 ; 104/DIG.1; 105/108; 105/172; 446/447; 446/484- A locomotive that's made from Erector Set parts and uses this toy motor.
2031769 Kitchen Utility Device, Alfred C. Gilbert (A. C. Gilbert Co), Feb 25, 1936,366/201 - mixer with optional juiceer that fits on top
2047025 Humidifier, Alfred C. Gilbert (A. C. Gilbert Co), Jul 7, 1936, 261/91 - less noise than others, uses the 1832456 electric motor
2154653 Battery Holder, E. N. Anketell, Apr 18 1939 429/97 ; 200/60; 362/120- a two "D" cell holder and on-off switch to power lights, small motors, etc.  maybe to have something smaller than a couple of No. 6 Dry Cells.

Patent 1195768 assigned to Knapp Electric and Novelty Co. of New York

I think that Gilbert bought out Knapp. 

This may be a Gilbert sewing machine or small appliance motor.  The shaft that's outside the pulley is tapered and shows signs of being used. 0.145 big end, 0.116 small end, 0.220 len.

6 Apr 2008 - a similar looking motor on eBay was called a Knapp motor.    A little Googling of patents found the Knapp Electric and Novelty Co. of New York.  The first patent I found assigned to them was:
1195768 Combined Reversing Switch and Brush Holder for Dynamo-electric Machines, Carl Bergman Jr. (Knapp Electric and Novelty Co), Aug 22 1916, 310/219 - the motor looks very much like the Gilbert shown above with the new reversing switch and brush holder added.

Pulley End	Shaft End with thumb nuts as the connection terminal

Electro-Magnetic Toy Engine - sounds like a gas or steam engine
Build it YOURSELF!, a REAL ELECTRIC MOTOR - Kit to make a 2 pole D.C. motor & modern version made today & Science First demonstartion motor -
MESCO 1011 Toy Engine - works like a steam engine
Weeden D.C. Motor -a 2 pole D.C. motor
No. 6 Dry Cell - and  Flash Amps as measured with Pocket Ampmeters
Self Winding Clock Co. "Western Union" clocks - uses electromagnetic motor to wind spring page 1, page 2 

Girders & Gears - A.C. Gilbert Erector Sets - History of the Erector Motor

Kt = 1352.4 / Kv,  Ke= Kt / 1.3524 , Ke = 1000 / Kv , Kv = 1000 / Ke
So what good is all this? It means that given a source of known rotational speed (an electric drill, or drill press if you have one), you can compute Ke for a given motor (clamp the motor shaft in the drill's jaws, measure the resulting open-circuit voltage, then do the math).
Ke, along with the above information will then give you Kt (so you can compute your motor's theoretical torque at any given current), and Kv (so you can compute your motor's maximum speed at any given voltage). If you can measure stall torque, you can then compute motor efficiency (measured torque expressed as a percentage of the theoretical torque).

The above web page is aimed at permanent magnet DC motors that can act as generators.  This motor when spun by hand only generates about 50 mv with the field series connected with are armature.