Is there a universal rule for servo drive gear placement?

I'm planning to use this servo for a robotics project, but I need to know exactly where the drive gear is located relative to the body. The technical sketch provides the other dimensions very nicely, but they fail to provide that important measurement.

I assume that one dimension is easily found by taking half the width, but the other dimension can't be eyeballed; although it appears to be roughly 3/4 of the length.

If anyone knows why they didn't provide this dimension and/or how I could find it, that would be greatly appreciated.

Note: If this isn't the right S.E. to ask this, would someone kindly point me in the direction of the correct one?

  • $\begingroup$ Indeed, due to rotational symmetry its same distance away from the body in both directions but there is no measurement for the body. Buy from other vendor. $\endgroup$
    – joojaa
    May 16, 2017 at 4:19
  • $\begingroup$ @joojaa That's the manufacturer's specs. I don't know why they'd include the other dimensions, but not that critical one. $\endgroup$
    – CoilKid
    May 16, 2017 at 4:25
  • $\begingroup$ @joojaa Ah! I think I see how I can find it. The drive gear is placed in a circle, the diameter of which is the width. The circle is tangent to three sides, so it must be located 1/2 the width from each. Perfect! Thank you for the enlightening comment about rotational symmetry. $\endgroup$
    – CoilKid
    May 16, 2017 at 4:32
  • $\begingroup$ They may have excluded the dimension simply because they thought that it was plainly obvious. Okay, glad to have THAT solved. $\endgroup$
    – CoilKid
    May 16, 2017 at 4:33
  • $\begingroup$ @joojaa One of the basic principles of dimensioning engineering drawings is "don't repeat yourself" (because if you do, one day you will make a mistake and give two different dimensions for the same quantity, and you don't know which number the reader is going to see first and believe is correct). The length of the body (23) is on view on the left, and from the view on the right it's obviously symmetrical with respect to the overall dimension of 31.8. People get lazy when they have 3D CAD models and can just measure off anything they need to know! $\endgroup$
    – alephzero
    May 16, 2017 at 5:43


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