Problem 5: The Mini-Mac Mobile (MMM) is a fun ride for kids who live on farms. I
ID: 1767383 • Letter: P
Question
Problem 5: The Mini-Mac Mobile (MMM) is a fun ride for kids who live on farms. It consists of a cart that is pulled by a minature cow (named Mac). We want to pick out a bearing that will work for the wheels of the MMM. The following is known: When fully loaded, the MMM and its passengers have a mass of 20 slugs. At full speed the MMM moves at 20 ft./sec. At full speed, the MMM can turn in an arc with an outside radius of 6 feet. When it is turning through this arc a good (conservative) assumption is that all loads are shared equally between the two outside wheels and the inside wheels are unloaded. The wheels of the MMM are 17 inches in diameter. The axle that the wheel is mounted to has a minimum diameter of 1.500 inches. The MMM should be designed to last 20 years if it is used at full speed for 4 hours per day. The bearing should have a reliability of 95% over the 20 year life. Using page 41 of the online Timken ENGINEERING Guide and page D40 of the the online Timken Ball Bearing Catalog, select a bearing that can be used for the MMM.Explanation / Answer
TIMKEN Bearing No 7201K. This is based on calaculation of mass of the MMM & its passengers. The given mass is 20 slugs.