6 



A BICYCLE ERGOMETER WITH AN ELECTRIC BRAKE 



commonly used on motor cycles, which was fitted to a large copper disk, 

 40.5 cm. in diameter and approximately 6 mm. thick. A wooden split 

 pulley (W, fig. 2) was also placed upon the hub for experiments in which 

 the apparatus would be driven by an electric motor. This has been of 

 especial value in some physiological tests on coasting in which the ergom- 

 eter was driven by a motor, the feet of the man being on the pedals and 

 revolving without doing any work. 



The apparatus was substantially 

 mounted upon a base-board by means 

 of iron braces. A type of handle-bar 

 was selected which could be comfort- 

 ably adjusted for the various riders 

 who were to use the ergometer, and 

 the seat was also adjustable to any de- 

 sired position. Provision was likewise 

 made for recording the revolutions of 

 the pedals by means of a mechanical 

 counter attached near the pedal-wheel 

 hub so as to be actuated by each pedal 

 revolution. 



The electro-magnet used for the 

 brake was made of a high-grade mag- 

 net iron, which subsequent tests 

 showed to be especially satisfactory. 

 The general construction and the 

 method of mounting are shown in fig. 

 2. The length of the magnet, exclu- 

 sive of the yoke, was 14.7 cm., and the 

 dimensions of the pole-faces P P' were 

 as follows: length, 6.4 cm.; width, 5.1 

 cm.; thickness, 2.8 cm. The magnet 

 was wound with double cotton-covered 

 magnet wire, substantially mounted 

 on a framework made of standard }(- 

 inch brass piping, and attached to 

 the iron braces supporting the bicycle. 

 Four binding-posts at the top of the 

 magnet provide for joining together 



the two magnet coils C C and likewise permit the connection with the 

 electric current used to magnetize the field and with the mil-ammeter 

 which measures the current. When mounted on the brass support, the 

 magnet was so adjusted that the disk D rotates in the gap between the 

 pole-faces P P' with approximately 1 mm. air-space on each side. The 

 upper edge of the pole-faces forms a line which is tangential to the cir- 

 cumference of the copper disk. 



Fig. 2 



Electro-magnet and copper disk of er- 

 gometer II. The copper disk D rotates in a 

 magnetic field between pole-faces P and P'. 

 Currents of varying strength are passed 

 through coils C and C, thus varying the in- 

 tensity of the magnetic field. The grooved 

 wooden pulley W is used to drive the machine 

 by a belt from a motor. 



