Okay, I've played with real numbers for a bit today and I've come up with this very ugly, marginally useless spreadsheet of data. It's attached to this post.
Again, this is all based on the initial equation for a differential that I mentioned earlier in the thread, but reversed for the purposes of this design.
To recap., it's:
output = (inputA + inputB) / 2
This means, of course, that our differential's range of output RPM lies from 0 to ~12,500.
Within that range, there are three distinct spheres of operation.
- In the first, found from 0 to ~2100 (coded yellow) the Chiaphua motor alone is more powerful than the output of the differential.
- From ~2200 to ~8000 RPM (coded red), the differential offers more torque than either motor could provide individually at that RPM. At best, this is ~30% more powerful than the drill and ~90% more powerful than the chiaphua as it approaches its free speed.
- From ~8000 to ~12000 (coded green) and beyond, the drill motor alone provides more torque than the differential.
Out of curiosity, I also looked at what would happen if the drill output was geared down approximately 3.5:1 so that it better matched the Chiaphua's free speed of 5500 RPM.
This is what has me most confused, now. Using the same formula, it appears as if by gearing the drill motor down, the small range where there's a benefit to the system ceases to exist. In fact, in all cases, it appears that a drill motor geared down produces more torque on its own than if it were input into this differential with the chiaphua running at its output speed.
The data for that can be found on the far right. It makes no sense to me, so perhaps there's an error somewhere. Beyond that, the original green, yellow, and red colored data seems to corroborate what Joe Johnson and Andy Baker have said -- as if they need corroborating.