official dewalt thread

[R.C.]

From Teched3

"Just to clarify, Buzz has been using DeWalts with a single CIM for the main drive for three seasons now, without any failure of motors or transmissions. However, we made modifications to the Joe Johnson NBD white paper to arrest certain concerns we had with the initial NBD design recommendations.

1- We do not cantilever the output sprocket/shaft, but support the output shaft on the outboard end with an additional bearing.

2- We fasten the output shaft to the end of the original transmission output shaft with 1/2-20 thread cross drilled and retained with a 1/8 hardened pin. We use the LH chuck retaining screw installed in the DeWalt output shaft, cut off flush to fill the void, so you won't break the carbide drill as it comes through the inner wall.

3- Where the 3rd stage is removed from the DeWalt, we insert an alumininum spacer ring against the transmission shoulder that acts as a depth spacer as well as to maintain the transmission/motor shaft on the drive axis.

4- We turn down the output shaft of the CIM to .250, and bore out the sun gear to .2505 for a sliding fit onto the CIM output shaft. The length of this reduced shaft diameter should be equal to, or slightly longer, (for clearance) than the length of the sun gear.

5- We machine the "top hat" of mild steel, index four 5-40 tap holes to match the pin locations of the sun gear, and tap for 5-40 FH socket screws. We also broach a 2mm keyway in the 5/16 bore of the top hat to match the 2mm key on the CIM shaft, and key it. We also cross drill (1/8) the top hat/CIM shaft and insert a 1/8 roll or tension pin.

6- We clearance drill and countersink the sun gear with a carbide 82 degree #2 centerdrill (5/16 OD, 1/8 point) and then drill the four holes out with a #30 (.128) cobalt or carbide drill to provide clearance for the #5 screws.

7- We add a stiffening 1/8 x 1 3/4 tension pin to the shifter rod to prevent the 1/16" shofter rod from bending.

We are planning to experiment with a 2 CIM adaptation to the above to reduce the amp draw of the single CIM setup, which limited our "gearing up" the drive for speed this season for Overdrive. The only tradeoff is the weight added for the CIMs and adapter ot mount them. Based on the weight of the robot, friction coefficient of the wheels, and amperage available to power the motors, additional motors for the drive only help to reduce the amperage drawn to the motors. In other words, if you don't trip the breakers, and the wheels slip on the carpet, more motors won't equate to more push.

I have also included some pictures of the DeWalts taken after a season of two regionals, lots of shifting, two tough after-season Invitationals, and demos to elementary school groups. They are tough, light, cheap, and easy to shift. Everyone always asks how we get so much on our robot. DeWalts go a long way to lightening for more capability in other areas of the robot. PM me if you have any questions.

Looks like the pics didn't attach, so PM me with your regular EMail address and I will send them to you if you want to look at them"