Mechanical Reliability

[ChrisH]

Originally Posted by billbo911

If I were to make any suggestion, these two mentioned above would be the two I would give.


I have seen a "Safety factor" mentioned a couple times. A ball park number for safety is to design for double what you think is the max. you will ever need. For example, if your arm will, at a maximum, have to support 8 pounds at full extension of 3 ft. Make sure you can support sixteen, or more. Also, don't forget to account for acceleration/deceleration forces of that mass. (Do the math!!!)By following the KISS principle, you may save a little weight. Use the extra weight to build a stronger arm.

Actually you are describing a STATIC safety factor. This assumes no acceleration (like being slammed by a robot). For my analysis on arms or lifting gear I assume the static load, add a 1/2g side load in the weak axis to account for getting hit. That gives a reasonable static load. I then multiply that by 4 to get a DYNAMIC safety factor. Actually the impacts we see will rarely push it to twice the load, but it doesn't hurt too much to add a little more. We have never broken a structure this way.

ChrisH