Alright, I know most of you all are going to hate this idea. I see the downsides and there's a good chance I'll be reverting to manual shifting when this is all done. That said, I think it would be a fun project, and it would be interesting to have an actual working product to evaluate and say more definitively why it sucks.

What I have in mind right now is a unit mounted on the transfer case, right near the shifter shaft. Some rough measurements show that it will require about 12 ft lbs over about 90° of rotation.

I haven't been able to find a servomotor with integrated worm gearing and the encodor on the output, so I think I'll have to find individual components. I figure worm gearing would be best for generating high torque and preventing the transfer case from slipping out of gear. I've never had that problem myself, but I've read about other people experiencing it (though I'm not sure if that's because of the transfer case or the linkage).

Control would be provided via an Arduino I already use for my radiator fan. A high-quality potentiometer would be used to measure shifter position. The Arduino would also monitor at least vehicle speed and throttle position to prevent shifting at incorrect positions.

The whole thing would be enclosed in a waterproof (or at least, highly water resistant) case. Because of the relatively small forces involved, I think mounting to the transfer case itself would be fine, but I'd rather avoid drilling holes in its housing if possible.

I went and looked for some actual products to start with a realistic baseline:

Shaft: The base of the shaft has a sort of rounded rectangular 'key' for the existing lever. It is about 4 mm thick, 9.5 mm wide, 19 mm overall length, and 17 mm along the straight part of the length. The end is threaded - not sure yet what the exact threading is since I can't measure it while on the vehicle, but it's about 8.5 mm wide and 16 mm long.

Worm Gear: Max diameter closest to the transfer case is about 60 mm. Could squeeze a bit more in if the part that fits on the 'key' is smaller, and lifts the largest diameter of the gear away from the case a bit. I'll probably want a bore no more than 9.5 mm so that I can file it out to fit over the key. Ratio will probably be ~20:1, but that can vary quite a bit depending on the final motor choice. With all that in mind, I'm thinking about this: bostongear.com/ecatalog?page=product&cid=worm_gears&id=CG1043

Nut: I don't think anything special will be needed here. Will just use a bit of threadlocker.

Worm: This will mostly be a function of the worm gear and motor chosen. This should fit my current configuration: https://www.bostongear.com/ecatalog?...orms&id=LVHB-1

Motor: With 159 oz-in starting torque, and let's say... 20% losses from motor to shifting shaft, that's a max torque of ~22 ft lbs - about double what I estimate will be needed. One issue I see with this motor is that the shaft is only an inch long, and the worm is a bit longer. It's also a smooth shaft, but I assume I could just drill a hole in it for the worm's keyway. I think it will still be more than sting enough with a <.1" hole.

There's also a space consideration. I'd have to push the worm a little away from the face of the motor to keep the worm gear from contacting it. That would mean only ~.75" of interface between the worm and the motor shaft. I *hope* that if the motor can be secured well, this won't be an issue.

Potentiometer: Probably will aim for something with a slotted end. Looks like this one might work well: https://www.mouser.com/ProductDetail...Nq75HyBEFgA%3D
Not happy about that price tag, but it's IP67 rated, has a long enough life it shouldn't ever need replacing, has a very low temperature coefficient...


Here's a model of what I have planned. (Anyone know where I can get a model of the 242 itself?) Worm gear, worm, and motor are all manufacturer models. The shifter shaft and potentiometer are close approximations:
https://i.imgur.com/NXMCmmc.mp4


Thanks for any input!

 

Lost my model when my computer decided to restart while I was at work. Oh well, made me make a better one with some updates.

Gear has been changed to brass, and a 30:1 ratio. All parts have been modeled accurately. The enclosure has been added (3 mm aluminum sheet). Overall size is 6.3" x 3.9" x 2.2".

I'm considering adding a sort of half-wall in the enclosure at the base of the worm gear (the brass one) in order to act as a sort of trap for grease.

The front face of the enclosure will be sealed with RTV and secured with some bolts I haven't added to the model yet.

One nice thing is that the brass worm gear will the one that sees any significant amount of wear (although I expect it to last for several years minimum). If it does become very worn, I will be able to rotate it up to 3 times since it has <90° travel in normal operation.

Animation of model.

 

Cool! I look forward to seeing the prototype.