Quote:
Originally Posted by Dale
Did anyone use shock absorbers, perhaps like these , on their robot? Given all the shock involved I'd love to find something to use going forward that doesn't add too much weight. |
The shock load of a crash like this can be impressively large. Here is a good paper that discusses calculating the shock loads and designing the isolations for it.
http://www.novibes.com/documents/fil...onAndShock.pdf
See the shock section where it discusses a "drop". C-Rio are rated at 50Gs (thanks Greg for the correction).
Battle-bots have been shock mounting their electronics for years. I believe that "Kicking-Bot" by Imaharra has a good section on this.
*Extra info*
An important thing to understand, when shock isolators are under-designed, they can actually induce higher "Gs" into the object being isolated. While this seems counterintuitive, this is exactly what happens in a car crash. When a car hits a wall, it begins to slow down the instant it touches the wall. For a 30 mph impact (standard test) engineers design for the car to see about 20G's. Thus the time for a crash is 30mph = 44ft/s & 20G's = 644 ft/s^2. Thus a crash averageing 20G's will last 44/644 =0.0683 seconds. The distance traveled during this time is D=1/2*a*t^2 or 0.5*644*.0683^2=1.5 ft. Now assume that the seat-belt requires about 2 inches of travel to lock, and your fluffy coat has another 1 inches of travel. This reduces your stopping distance to 1.25 Ft. Your time also gets reduced by Distance .25 ft=1/2*644ft/s^2*t^2 => t=0.0279. thus your new time is 0.0683-0.0279=0.0404 seconds. To figure out your average rate of deceleration then take your speed a=44ft/s/0.0404sec=1088ft/s^2 = 34Gs. This numbers gets even worse once you add in chest compression and belt streatch. Often in a car, you will feel 2X the decel rate the car sees during the impact. For cars, this is why they have air-bags. The air-bag deploys so fast, that is helps you start to slow down sooner. In Racecars, this is why you where your harness extremely tight.