Depending on how heavy the bed is (mine is 5.4lbs), a 4:1 ratio gearbox will not hold the weight of 1/2 the bed and the rear lift system will drift. I added an additional 2.2lbs with the u-joint assembly. The 4:1 ratio gearbox on the front arms is enough to hold 2.7lbs/2. So in the end we get no drift on power loss and the motors are not driving additional weight.

The idea of the front arms it purely to hold the bed up from bouncing from a traditional cantilever bed. The bed being uncoupled from the front arms allows the bed to pivot, in two directions, without being constrained. It's vertical travel has no effect on the bed's position laterally and thermally will not be issue to cause binding. Another plus to this is the front vertical rails do not need to be accurately mounted. The vertical movement's accuracy is all controlled from the rear. Most designs have the lift arms in the corners due to the availability of that corner extrusion. What better place to put one where a mounting point is already there. The bed's bolt holes are usually further in from the corner and make the lift arms long to reach. This creates additional moment on the carriages and any deflection/backlash, torsional, will cause the bed to move/twist. The only allowed movement of the balls or cup magnet in the front is from either deflection of the rear extrusion(or even the V block assembly) or thermal expansion. It literally cannot move much under those conditions. Now if you want to get into non planar printing, there is only so far the lift arms can be out of alignment, vertically, before the balls will fall off the arms. Maybe 50mm or so. But I didn't make this to do non planar printing. For that I could have made the front lift arm pads bigger.

@@MrRocksalt 😬 sorry, should've said, I'm a CNC machinist, so I get the kinematic constraint concept. Great explainer tho👌 So if I'm understanding ...despite making for a longer arm, and reducing the area to mount a bed heater... it seems everyone designs around the existing in-board bed mount holes because they're placed by manufacturer🤷 Sorry to repeat myself: with the 2 front balls mounted on the sides of the bed... could you still fit a sufficient XY thermal accommodation mechanism between bed & carriage? (Assuming one is only doing planer printing.. a tiny compliance joint should be sufficient, yeah?) I have to figure it's just beyond most hobbyists to drill and tap mounting holes on the edge or corners of a large bed, because I've never seen anyone do this. It would be a win-win right?!?.. p.s. Hats off to you sir, admire your expeditions into 3D printer design! I'm thinking about what designs I'm going to adopt and refine when I get around to building a printer (I'll be sure to give credit in any posts ☺️) Thanks for the conversation! 😁

@@Metapharsical Yes, if the ears were welded on or you have a custom plate made, having ears on the front would be good(I have seen some like this already). Many ways to cook eggs :) I just thought this design was neat and wanted to try it. Hard to do for most people and jury is out on it's viability. Still printing on it to see what happens.

You could also build a frame under the bed to reach the carriages and use maxwell /kelvin couplings

It's a Kinematic bed system. Heat causes the frame to move, this displaces the bed and the belts/lead screws/whatever, allow the bed to be trammed to form a plane. It removes the need for bed adjustment screws to fine tune as the steppers re-align the bed automatically.

@@MrRocksalt Displacement as in bed is not level once frame heats up? Also, how much movement are we talking about here?

@@user-lx9jm1wo3h I don't want to go into details here with pictures and data, but it's enough that they have these systems! Not only that, when the bed is rigid affixed, the heat causes the bed to bind during Z moves, making inconsistent layers. We are talking chamber temps from 50C to 90C(122F-195F) or more. This is quite warm!

@@MrRocksalt I see. Thanks for all the info on that.

Cantilever beds will bounce in the front and this system has freedom to pivot and thermally expand without being constrained. Cantilever beds are usually supported by 10-12mm rods and IGUS bearings, which are sloppy.