15T CIM Shaft Pinion Gear (DeWalt project)

[craigboez]

As an offseason project I bought a few DeWalts and have been working on an updated NBD type transmission. My goal is to take the original idea but morph it into a direct drive system (similar to this 1213 setup, but without removing the first stage of the DeWalt transmission). Long story short, I'm looking for a 15T spur gear/pinion with an 8mm bore and 2mm keyway so it can be mounted to the CIM shaft and plugged directly into the DeWalt tranny without modification.

Has anyone done this? If so, any suggestions, and in particular, who sells gears like this? SDP-SI seems to have the best selection, but they don't have exactly what I'm looking for. Also already checked: McMaster, Boston Gear, Small Parts, Martin Sprocket, Google, etc.

[Jack Jones]

The second stage planet gears in the DeWalt (the longer ones) are the right size to drive the transmission. Just buy an extra tranny and you'll have five to use as pinions. We use them all the time for a FisherPrice hook-up by having the pinion EDMed to 0.127" and press it onto the FP shaft.

I doubt that there would be enough meat on them to EDM them for an 8mm press fit. I guess if I were doing it, I would turn the CIM shaft down enough to press into the gear. But then, I wouldn't be doing it because removing the first stage planets and using a disk to drive the carrier pins is a whole lot easier to do.

BTW: With the first stage left in, you can expect to see 160, 480, and 640 RPM no load output for 1st, 2nd, and 3rd gear. With it removed, you get 480, 1440, and 1920.

[craigboez]

Hey Jack

Thanks for the reply. I was thinking of PMing you directly, so this worked out well.

My motivation for leaving the main stage in is to get a lower RPM so we can actually use the shifting capability of the transmission AND get the benefits of direct drive. I'm guessing with your setup you don't use med and high gear (at 25 and 33 ft/s)? Using 4" diameter wheels and keeping the first stage in gives theoretical speeds of 3, 8, and 11 ft/s - which seems fairly ideal for slow, med, and fast bot speeds.

Buying an extra tranny to steal pinions from is a great idea. Thanks for the input. How would one go about turning down the CIM output shaft? Can that be done reliably without damaging the motor?

[sanddrag]

Originally Posted by craigboez

How would one go about turning down the CIM output shaft? Can that be done reliably without damaging the motor?

I would imagine you could probably chuck up the entire motor in a lathe, power it from a battery or power supply or whatever, and take VERY light cuts, and probably be fine. I wouldn't really recommend this though. Suppose you cook a motor during competition? Are you going to have modified spares on-hand. Perhaps you may want to design your drive system to use the motor as-is.

[Jack Jones]

How would one go about turning down the CIM output shaft? Can that be done reliably without damaging the motor?

IDK - I'd hate to give bad advice, not having done it and knowing I'd probablly lose a CIM or two in the learning process.

FYI - We got about 8 fps with the 4" wheels locked in low gear. We attempted shifting in '06, but it was too unreliable and wasn't worth the hassle.

Attached are the DXF files for the adaptors we use. They are ready for watercutting - on an Omax, and maybe a Flow (since they're now the same company). The meaning of the layers (colors) are as follows:
0: Traverse
3: Cut w/ quality = 3 (normal)
5: Cut w/ quality = 5 (slow precise cut)
9: Lead In/Out

Good luck...

EDIT: use 0.25 - 0.27" stainless or TI for the adaptors

[craigboez]

I got some advice via PM from Teched3 on how they turn down the CIM shafts. To summarize what that message said:

* To turn down CIM shaft on the lathe, disassemble the CIM and secure the tail end of the shaft in a collet.
*Centerdrill the other end of the shaft (transmission side) using a bushing to center a 5/16" centerdrill. Now that end can be supported by the lathe tailstock with a BB center.
*Turn the shaft end down where it is supported by the tailstock. It has worked well for us for about 4 years.

This process sounds fairly straight forward, but also a little complicated for what I'm trying to do. I'm really looking for an easier solution to this DeWalt/CIM interface issue. Any other suggestions?

EDIT - I'd also really like to keep all the parts un-modified, or at least as close to COTS items as possible.

[JDNovak]

I know you are looking for someting simple but just to add another tested solution. . .

We interfaced a CIM to the first stage of the Dewalt by milling the CIM shaft into a hex. I believe it was done by chucking the end of the shaft in an index head and milling the exposed part. After the hex was complete the end of the shaft was cut to the insertion depth. I don't think the motor was even dissassembled.

The pinion (taken from another gearbox) was EDM'd to a mating hex. No fastener to the shaft was needed.

We put extreme pressure on the resulting gearmotor by driving the first joint of an 8' arm. The backdrive pins failed a time or two but the motor interface survived the whole season and still looked good. During the offseason we even used it to pick up chairs and stack them as a demonstration.

[Greg Needel]

I was thinking about this and if you want a direct drive solution why don't you get the interfacing gear and mount it to a shaft which can then be coupled with a flexible coupler (spider) to the cim motor. It would require the use of another bearing set, but could be done without modification of the cim motor or transmission. The only downside I see is that it would not be a compact package.