Turntable Bearing Options
Bearing Selection
Key Bearing Loads (No Safety Factor Applied, Max Value Estimations)
| Load Type | Symbol | Value | Units |
|---|---|---|---|
| Radial | FA | 50 | N |
| Axial | Fr | 160 | N |
| Moment | M | 130 | Nm |
Note that these are the actual estimated forces, not the equivalent bearing loads. Once we nail down a general selection, we should like to supplier data sheets for load estimation.
Bearing Options
There are many options available for a turntable. However, based off of some minor design research and sketching, I think it would be pretty useful if we can select a face mount bearing with mounting holes on the inner outer race, as shown below. This may be design fixation, but it seems like selecting such a bearing would help with load distribution and axis mating using minimal parts.
This is a very lightweight option we can use if we want to minimize our mass for the bearing, as it uses plastic sliding elements to significantly reduce overall weight.
https://www.igus.com/product/18969?artNr=PRT-04-60
Note: Specs shown above for 120mm diameter variant
| Pros | Cons |
|---|---|
| Very lightweight (250g) | Low Safety factor on tilting moment although larger (more expensive) variants may increase this load rating |
| Relatively low cost for a new slewing bearing (167 USD, plus shipping probably) | Does not use ball bearings or rollers, but plastic as the sliding element (iglide material). Not too sure how good this stuff is |
| Large-ish diameter profile, should give ample space for mounting the base of A2 | |
| Quick Lead time on website (2-4 days) |
Note 2: igus also has other slew bearing options that are heavier and more expensive with higher load ratings, like this one: https://www.igus.com/product/643?artNr=PRT-01-50. however, I think the main selling point of the igus bearings is the light weight variants - if we are going to use a heavier option might as well get something with ball bearings that will be more reliable in the long run for a similar mass.
Another option is buying a used crossed roller bearing (VERY similar to slew bearing in application) off of eBay or Alibaba. Many Chinese vendors resell used crossed roller bearings from THK, a Japanese bearing supplier.
https://www.ebay.ca/sch/i.html?_nkw=cross+roller+bearing&_frs=1&_oaa=1&rt=nc&Brand=THK&_dcat=185120
There are MULTIPLE options for part numbers, sizes etc. Here is the analysis of one such example.
https://www.ebay.ca/itm/193821899017?hash=item2d20af7909:g:hlcAAOSwtBZf5rty
Finding the exact product specs for this part have been difficult, as I don't think THK continued this specific part model. Waiting on an email to hear back from them, below are some sketchy chinese datasheets. 
That being said, other models can be found online.
| Pros | Cons |
|---|---|
| Cheaper way to get actual crossed roller bearings | Quality is not guaranteed as we are buying used |
| Very high load ratings, no major concerns on loading failure | Lead times may be unreliable from vendors like ebay or aliexpress |
| Mass is not crazy high, as ball bearings are much smaller and stronger compared to igus bearings | |
Equivalent Bearing Load Calculations
Note: Although this information may vary by slightly supplier, I just took the calculations from a reputable looking source and figured that the constants would be relatively same.