'Distance' marathon - a review ..............................................by Alistair Nicoll NO.1 CLOCKWORK MOTOR MARATHON by the Meccano Society of Scotland The challenge was simple; make your no.1 Clockwork Motor travel as far as possible on a single winding. Five members of Meccano Society of Scotland entered and all took different approaches. What they were all doing,(although they may not have realized it!) was to optimize the function pi*DN as this represents the distance traveled. In the formula D is the diameter of the driving wheels and N is the total number of revolutions made by the shaft on which these wheels are mounted. Like all engineering problems however, it turns out not to be as simple as that. If it were, the model with the largest diameter driving wheels would have won - and it did not. The complication is that the value of N can be changed by gearing the drive shaft up or down from the motor shaft. The temptation is to gear up as a drive shaft going at e.g. twice the speed of the motor shaft will complete double the number of revolutions and hence double the distance. Hang on a minute though, there is another variable, to wit the torque of the motor. If you gear up you reduce the torque available to rotate the driving wheels and this could make your model stop. Four major approaches to design were evident: 1. A "traditional" design, with the driving wheels geared down from the drive shaft by about 3:1. 3" Pulleys with tires were normal driving wheels. 2. A simple design with 1" Pulleys with Rubber Rings connected directly to the motor drive shaft as driving wheels. 3. A friction reducing design where the drive wheels were not journalled in normal bearings but rested between overlapping Face Plates which were free to rotate in secondary bearings 4. A variation on the simple design with the drive wheels 6" Pulleys. This competitor bent the rules by asking for a second "go" with the pulleys replaced with Circular Girders (diameter 5.1/2") 5. An original idea which involved suspending the motor on a single drive shaft which bore two Circular Strips (diameter 7.1/2"). The drive to the shaft carrying these was geared up from the motor shaft by 2:1, a 2" Pulley on the motor shaft driving a 1" Pulley on the driving wheel shaft. As the motor tended to rotate about the road wheel shaft a 2" Pulley was mounted in the side plates to make contact with the ground if the motor swung too far. A side effect of this clever design was that the swinging of the motor actually helped the device along as, if it slowed through hitting some small discontinuity in the floor surface, the motor would swing forward and, in swinging back, would give a small impetus to the whole device. Results are given in the table below. Congratulations to Chris Shute on a brilliant solution to the problem. Name Design type Distance travelled Jackie Inglis 1 12.3m Bobby Middlemas 1 17.0m Peter Hodkinson 2 31.9m Bert Hutchings 3 35.9m Alistair Nicoll 4 108.5m Alistair Nicoll 4 119.7m Chris Shute 5 180.0m Of course, the one variable that has not been discussed at all is the actual running time of the motors in the unloaded state. It would have been interesting to compare these results as well.