1) If you put the motors on top, you need something to terminate the short lead screws into.
2) Most of the torque and force is on the plate that has the motors and screws in common. That would mean a fairly heavy top plate.
3) If all the electronics and control are going to be closely coupled to the motors, they would go up on top as well. Same thing for the power supply.
Most of that simply makes the printer top heavy. The real issue is how to do the mount so it does not bump into the arms. Since you have a bearing and end clamp, there must be some non-zero increase over the shaft diameter. You need some sort of structure to solidly hold the bottom of the shaft. The most likely ways to do that will also increase the "bump zone" for the arms. I suspect you would have a larger bump issue this way than with the motors mounted above the lower plate.
If you put the motors on top and keep the screws full length, there's no real advantage to the top mount motors. Weight low is always better than weight up high stably wise. It's also a lot easier to get cables in and out if it's all low....
2) Most of the torque and force is on the plate that has the motors and screws in common. That would mean a fairly heavy top plate.
3) If all the electronics and control are going to be closely coupled to the motors, they would go up on top as well. Same thing for the power supply.
Most of that simply makes the printer top heavy. The real issue is how to do the mount so it does not bump into the arms. Since you have a bearing and end clamp, there must be some non-zero increase over the shaft diameter. You need some sort of structure to solidly hold the bottom of the shaft. The most likely ways to do that will also increase the "bump zone" for the arms. I suspect you would have a larger bump issue this way than with the motors mounted above the lower plate.
If you put the motors on top and keep the screws full length, there's no real advantage to the top mount motors. Weight low is always better than weight up high stably wise. It's also a lot easier to get cables in and out if it's all low....