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Nick
Experienced Roboteer
Joined: 16 Jun 2004
Posts: 11802
Location: Sydney, NSW
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I looked up this comparison of plastic bearings and Nylon is right down the bottom - PTFE or MDS Nylon looks like a better bet:
http://www.mcmaster.com/#sleeve-bearings/=38pj86
The ratings for plastic bearings are specified the same as for bronze bearings, the actual numbers for nylon are WAY lower than for metal bearings. Have a look at these design formulas:
http://www.mcmaster.com/#about-plain-bushings/=38pszl
.
For your bot with Dewalts in high gear and using four 1.25" ID by .75" wide bearings, I get the following:
Regular driving around, V=569.85, P= 6.67, PV=3,799. Nylon bearings can handle the load but not the velocity. the PVmax is too low as well.
Driving with another bot on the wedge: V is the same, P = 13.33 (double) and PV also doubles to 7,598. Nylon will wear out pretty quickly with a PVmax of only 3,400
Firing the weapon will put a huge shock load on the front bearings, could easily be 5 to 10 times the normal running load. This could easily deform plastic bearings.
In contrast, Bronze bearings have PVmax ratings of around 50,000 to 75,000, which looks like it will cope well in all situations. Needle roller bearings also exceed the load and speed requirements.
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Wed Aug 19, 2009 12:45 am |
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