Drill motor gear measurement

[Tristan Lall]

Try this. (From FIRST's 2003 spec sheets.)
But watch out for this. (From FIRST's 2004 spec sheets.)

Notice, that the documents are not the same! The 2004 describes a 13-tooth gear, and the 2003 describes a 15-tooth gear. The 15-tooth gear was used in 2004 and 2003--the 2004 spec sheet is in error. (I've linked to it, because it may be easier to read--but use the numerical values from the 2003 sheet.)

Also, PIC Design is just about the only source that anyone's been able to find for 0.7 module gears (high-precision metal ones, anyway). They've been very slow with orders (think 1-2 months, when they promised a couple of weeks, even with nagging phone calls, etc.), so it might be wise to order ahead. If you think you can make them work, Stock Drive Products has plastic moulded spur gears in 0.7 module, but they obviously aren't as strong or as precise.

Also, I've found that the drill motor pinion seems to like a little bit of extra centre distance, in order to mesh correctly (due to a slightly enlarged, non-standard tooth form). I'd suggest using about 0.007" to 0.010" extra centre distance, to allow for a better mesh. If you use the standard theoretical centre distance (based on pitch diameters), the gears will mesh too tightly.