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Old 08-28-2012, 12:18 AM   #148 (permalink)
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Reinstall transmission Aug 27

I went to a mechanical supply company today to pick up a coupler that I thought would work for connecting my electric motor to the drive shaft ... somehow I misunderstood at some previous time because I thought the solution was off-the-shelf and was stocked. This time, I went through 3 possible solutions with the tech and none of them will, it appears, work. I believe him - I'm a bit unclear as to what I thought was a solution, and who I had talked to.

So - a bit of a shock ... and where do I go from here? The project has had a few challenges and is now going in a direction that I would not have chosen from the start. Now it appears that the mechanical coupling of the electric motor and the drive shaft is quite a problem. The size of the motor shaft is 2.125 inches, or two and an eighth. We looked at three couplers - taper lock, like for a pulley, weld-on, where the coupler has a key-way and slides onto the motor shaft, then you weld whatever your like to the end of it, and chain sprocket, which is very similar to the weld-on.

All of them are built to deliver a lot of horsepower. These weigh several pounds each and their outside diameter is 4.375 - 4.5 inches. This outside diameter is larger than the end of the drive shaft.

And to put the icing on the cake, all the couplers are special order. It appears that motors and gearboxes with that size of shaft normally deliver hundreds of horsepower for short periods and over 100 HP continuously.

This is a bit of a problem. I have enough of the truck assembled pretty close to how it was originally so that it should move, and now I can't deliver any power to the power train.

I have a couple of smaller motors, that I could line up with the drive shaft pretty well. Still no way to couple the motor shaft to the drive shaft. They don't deliver enough torque to move the truck. I pretty much proved that by moving the truck from it's old parking space onto the concrete pad.

With a 3 foot bar on my ratchet direct to the rear differential I could move it over a couple of small bumps. But I could not push it - so 250 lbs force on the ground is not enough. The pressure on the bar was not huge, but more than 50 lbs for sure. So I need the torque that the 40 HP can generate, but I can't drive the front drive shaft. 50 lbs on a 3 foot bar is 150 to the rear diff, it has a 3.43 ratio so there is 515 foot-lbs torque to the wheels, and since they are an effective radius of 13.85 inches, that gives 445 lbs of force to the ground. That seems a bit high since I was close to keeping the truck moving ... well, 50 lbs was a guess on my part .. maybe 30 lbs is a better guess?

Start with what I need. Moving the truck on small bumps, is 50 lbs of torque on a 3:1 pry bar, so 150 foot-lbs at the rear end, 515 foot-lbs on the rear axles, 445 lbs force to the ground.

If I use a small 5 HP motor - 15 foot-lbs is rated torque. So a 10:1 reduction would be needed. A chain drive or a belt drive to the rear drive shaft (which moves up and down with bumps) would require 12 teeth and 120 teeth. The driven sprocket is almost the size of a tire.

How about 2 of those 5 HP motors both driving the rear drive shaft? 5:1 is much easier. 12 teeth driving 60. It would have to be pretty close to the support point for the drive shaft, and tensioning the chain would be ... interesting. I think this is possible.

How about the 40 HP. 120 foot-lbs is rated. 150 would be 5:4. 40 teeth driving 50 teeth. Or 22 teeth driving 26 or 27. I'd have to make it fit into a standard range. It will be tough to get the motor close enough to the support point for the drive shaft - the cab is sort of in the way. I think that this 40 HP motor is just too big, too hard to move around, too hard to deal with. It was a good deal surplus, but it was not a good fit for the truck.

I'll get the bolts put into the transmission mount, the drive shafts, get the transfer case bolted onto the transmission, and see what I can come up with for the mount on the front of the transmission, the bracket to attach to the motor mounts, etc. At that point, I need to get some yard work done that has been piling up for ... 3 weeks now ... and I guess I will not be moving SalvageS10 under electric power this month.
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