[SteinHDan]

Thanks Mark and Ben! :-)

This electric version even exceeded my expectations. I was planning on testing the electric motors and then converting to hydraulic if it didn't work out. And I didn't actually think it would work, because the arm is so long and the leverage it puts on the motor axle is enormous. But it did work quite well and it can dig normal dirt, which was the goal.

it even dug that gravel you see on the video. That's pretty tough stuff to dig.

I also got rid of that gear backlash I discussed with Joe previously. It was by most part caused by a machine key inside the gear motor that wore down and not by the gears themselves. To combat this I welded the gear motor's final gear to the axle. The weld looks so bad that I don't think I can show it here.. but it works and removed the backlash. I've only done it on the stick motor, though, and I'm planning to do it on all the motors.

The gear motors are so strong (320kg/cm) that they will rip themselves apart if not limited in some way. That's why I added the current limiting and the position sensors.
I've set the current limiting to match the scale force of the original full-size machine. For example, I've set the current limiting for the boom so that it can lift 12kgs. Multiplied by the scale (1/14)^3 (three dimensions), we get 12kgs * 2744 = 32928 kg which is around 33 metric tons. That value is close to what the real machine lifts with the same arm configuration and arm position.

So, the machine doesn't need to be any stronger to be a scale replica of the real CAT 390. I still don't feel too well about the leverage the arm has on the motor axle, though, so I've been thinking of maybe adding an external final gear that bolts directly to the arm and not feed the force from a 1m long arm through a 10mm axle. That also would remove the need to weld inside the gear motor.

I guess the things I like best about it being electric is that it's very quiet and there's no oil anywhere.


Stein :-)