- Cody Harris wrote:
- Ive always felt bronze was to heavy, plus you can get to higher speeds with bearings
This brings up more food for thought (Dan has touched on a lot of this as well)
In building combat bots with weight limits, we are always looking at what components weigh.
In my simple example above, you might find that a simple thin wall bronze bushing might weigh less than a bearing(s).
Some other factors to consider are: (please note that these are very general statements)
1) Speed....rolling elements such as bearings are generally better for high speed applications.
2) Load....bushings will generally support MORE radial moa than bearings. Ball bearings are the worst, in that they only have POINT contact...i.e. the load is supported by contact between the balls and the iner and outer races of the bearing. Needle bearings are a better choice if radial loads are high. Bushings have the most surface contact and can support a large radial load. Other bearings such as tapered roller, cylindrical, etc. could also be considered, but they also have thier limitations.
On the other hand, ball bearings can resist some AXIAL loading (about 1/3 of their raial load rating), while needle bearings provide NO axial load resistance. Bushings can be designed to support axial load. Tapered roller and angular contact bearings provide both raial and axial support.
3) Friction...rolling elements such as bearings create much less friction than sliding components such as bushings.
4) Lubrication...In most combat robot applications, grease lubrication is desirable. Some greases can also be used at fairly high speeds. In extreme speed applications, oil lubrication is preferred.
5) Component life and service factor...Items 1 thru 4 above all play a role in determining how long components will last.
Shock load is often either overlooked or underestimated. For example, A ball bearing of a certain size might be a good choice for a simple pulley rotating on a shaft, that won't see much shock loading, but in the case of a wheel that might hit the ground from 5 or 10 feet in the air, it may not hold up. When choosing components, we need to add a service factor to the expected load ratings.
6) Machining of components...For longest life and best performance, machining accuracy of shafts, housings, etc. must be considered. Bearings generally require higher machining accuracy than bushings.
More to follow.....