It’s been a little while since I went “Make it your damn self!” on the DeWuts and left everyone hanging with the waterjettable pieces. Since then, the billet style design has evolved some. I’m proud to announce that it has been sent off for manufacturing by Sketchy-Ass Chinese CNC Co. Ltd., to return to me hopefully by mid January. This is a product which is in immediate need by robotland ever since the old style 18v DeWalt “Team Delta” systems stopped manufacture, so, oddly enough, it might be my “launch product” instead of Ragebridge! Here’s what’s been going down.
This is the fully modeled design as of two weeks ago or so. As can be seen, I’ve actually bothered to model the DeWalt 3-speed gearbox! I’ve made the gearbox and motor available as a downloadable widget, if you want come up with your own design. The files are in Autodesk Inventor 2012 format, as well as a STEP and Parasolid.
While I tried to make a workable output shaft for the motor, I began to realize that it was perhaps more fruitful to replace the final output stage altogether. The 3 speed DeWalts have an advantage here because their antibackdrive (“that thing which makes it so you can’t crank on a drill’s chuck and have the motor turn”) system is very simple and planar. The idea would be to replace that ABD stage with a custom-machined ‘socket’ of sorts that wraps around the output carrier and has an integrated 1/2″ keyed bore, so in principle any 1/2″ keyed shaft can be used with the motor. If this is not clear from the above picture, then it will surely be elucidated by…
So, basically, the output stage planetary carrier has 5 little claw things. It’s easy enough to make a doohickey that wraps around those 5 claws. Normally, roll pins fit between those claws which are just barely smaller than the distance between one face of the weird decagon output coupler and the outer ring with 4 nubs on it (seen in the previous image). If you attempt to backdrive the drill, the decagon hub turn just enough to wedge the roll pins against the outer ring, locking the whole thing up solid.
This whole arrangement of course contributes much backlash to the system. While I could just say “take these 5 little derpy pins out”, that’s one more step in the instructions which, if not followed, would surely result in undesired behavior as the ABD rapidly alternates between locked and unlocked. A custom output coupler would also alleviate those concerns.
This is what the output coupler looks like, a 5-sided flower thing. In real life, this would be waterjet-cut from a high alloy steel like 4140 and moderately hardened. The shafting is a piece of stock McMaster 1045 steel shaft I bought to test fits.
The new output carrier pushes right against the inside of the inner ball bearing due to a chance alignment of English and Metric units. So, it truly is bring-your-own-shaft – the motor doesn’t provide any retainment force.
With this problem taken care of, I began addressing some fine details. With larger, heavier motors like this, face mounting screw holes are often not enough to keep the whole assembly planted under shock loads. A second set of mounting holes is provided at the rear to keep the heavy motor end anchored. These holes are designed to be 3″ apart and 1.375″ between centers. Why the weird dimensions? Because it’s compatible with a Banebots P80, just like the front mounting hole pattern.
This revision of the design also saw these little gearbox-retaining nubs on the inside, which help with setting the torque clutch tightness without having the motor installed yet. It allows more modularity in the assembly since previously the motor was the only thing pushing back against the torque clutch plunger (pressing on the spring steel wear washer immediately next to the gears, anyway).
The next logical step in the design was to combine the 5-sided flower thing with a shaft. This would fully constrain the output shaft, allowing direct coupling to a wheel.
Here’s what the whole thing looks like in mushy 3d printed plastic form:
This is the version I’m sending out to be manufactured. The integrated shaft is specified to be made from 1566 steel as-rolled 1″ (/25mm…) round, which should offer a yield strength in the mid 50s to 60ksi (400-ish MPa in Unamerican Units). So, the total setup if I were to kit this up would be:
- Integrated output shaft
- Output mount with 2 FR8 type ball bearings
- Motor mount
- Motor clamp
- The nifty barrel shifter holder
- 4 hex nuts to constrain the NBS holder
- 4 long cap screws to hold the output and motor mounts together
- 2 short cap screws to screw down the motor clamp
- 1 set screw to adjust the torque clutch
- A retaining ring, because retaining ring.
I’m wondering if I should make a version that has the “socket” output carrier such that the motor can hitch into any existing 1/2″ keyed shaft. The 5-sided flower thing will likely be available separately. I’m also going to pre-emptively make it available in downloadable form for your own waterjetting amusement (Inventor, ready-to-cut-DXF, STEP, and Parasolid). I strongly advise making it out of a high carbon or alloy steel for strength reasons.
For now, enough product development. I need to turn my attention to more pressing matters…