[brian_]

I recently purchased a set of love joy couplings before realizing that it wouldn't work out because it was too small for the Warp9 motor I'm using. Here are some pictures to show what I'm talking about:
View attachment 127364 View attachment 127363 View attachment 127362
The motor shaft is too long for the coupling so it sticks out (shown in first image) so when I put the second part of the coupling on, it doesn't sit all the way on properly leaving space in the middle (shown in second image). If I lift the bottom up, then it fits properly but it's elevated from the motor (shown in third image). If I put a key in and used the hex screw to jam the key in place, would that keep the coupling safely elevated and connected or is that not reliable?

Why are you insisting that the motor side of the coupling sits against motor case? Of course it can't touch the case because it would rub; the coupling is mounted on and located by the shaft, locked in place by the set screw, not the motor case or any step in the shaft diameter.

Here's a collection of support information from Lovejoy, which might help with understanding of how these couplings are used:
Product Resources – Installation Instructions, Videos, Catalogs
You appear to be using a keyed and set-screw equipped type L coupling, so the guide would be Jaw Couplings L-Line (L, AL, SS, C, H) Installation Guide (plus the accompanying video). As the guide explains, the face of the hub is normally aligned with the end of the shaft, and the exact positions along the shafts of the hubs are adjusted to give the correct space for the spider.

 

[brian_]

Motor torque output is basically proportional to current. The combination of 72 volts and 335 amps is enough electrical power for the 32 horsepower listed, but that combination of voltage, current, and power won't occur at either 5,500 RPM (that will be maximum speed) or 70 lb-ft (that will the maximum torque, at a lower speed); the 32 HP is a rated power for some condition that they think can be sustained, and perhaps the 70 lb-ft is for another sustainable condition, but the peak torque and power are both higher. The performance data for the WarP 9 at 72 volts shows 100 lb-ft (1200 lb-in) at 500 amps. That puts the Lovejoy L150 right on the edge for a WarP 9, and of course with more voltage and a controller able to handle more current both torque and power can be higher.

 

[brian_]

I have a 500A semiconductor fuse so even if I hit 500A, the fuse will blow, cutting off all power. Considering this and the fact that my system will be running on 88V nominal (96V peak), I think I'll be safe using the L150 lovejoy coupling. Do you agree?

It's on the edge of torque capacity, and speed would need to be limited... but the data says yes.

 

[brian_]

... the long and the short of it is that LoveJoys are very good at lower RPMs and torque loads that rise gradually (relatively speaking). In real world conditions of an EV, you've got neither of those, and the pliable center "spider" just eventually gets chewed up. Additionally, the little bit of "play" that you get with a LoveJoy that is seen as one of its advantages in many of its applications turns out to not necessarily be to your advantage, again, in a typical EV conversion. You end up with unwanted unbalance. A solid coupling between your motor and tranny is most desirable. Think about it like this, if a LoveJoy-like connection was what was best between a motor and transmission, then automakers would have been using them (or again, something like them) for a long time now.

There's no need for a compliant coupling between an engine and a transmission bolted to it, but in the propeller shaft (the drive shaft from a transmission in the front to a final drive in the back) many cars still use "giubo" or flexible disk couplings, which is like a traditional Lovejoy with the rubber part bolted to the yokes. It can work, but it's not a desirable thing, especially where compliance is not needed.