EC750E brain dump

I'm still waiting for parts, but some have come in. The double rims with studs as a sprocket does fit well in size, but does not drive the track at all. I'll either have to use spur gears elsewhere to drive the track or use something else for a spur gear.

While I've been waiting for parts for the shoes I thought about tackling some of the other problems.

One of them is the drive system. The Volvo EC750E has a two speed automatic gearbox per shoe. This permits both high and low speed. It would be nice to have this in the model so what are the parts required. Two motive sources(maybe XL motors), two transmissions(one per shoe), one battery box, one receiver. Due to the rotation of the body I'm expecting to need to locate all of the parts below the body such as in the X-frame and shoes. I find the automatic transmissions done in Lego to be a bit clunky, but they work. I've also looked into Lego CVT transmissions, but they have a big problem in that if rotation is entirely stopped on the output shaft the internal gears battle amongst each other to counter-rotate and torque to the output shaft is lost. This will not do. I'll have to revisit the CVT concept as I would love to have a smooth final drive ratio like say 1:20 to 1:4 depending on the friction of the environment driven on.

The large technic turntable is roughly 7 studs wide, but I need something closer to 11 or 12 studs wide for the model. I've been playing around with all sorts of ideas about how to accomplish this like support rollers front and back, but none have stood up to tests very well. I'm not leaning towards a hybrid technic/system brick solution wherein the force on the turntable will be distributed across a 12L brick built ring and an internal turntable. First try at this resulted in parts pulling themselves apart because of an inability to anchor the weight of the body to the X frame. What I've come to as a solution in to have two stacked central large turntables so that the one on the bottom can pull up on the X frame from underneath and the one on top can push down while sharing the load with the brick built 12L ring that acts like a fixed washer/bearing. There is enough space to have an 8 tooth spur gear driving a type 2 large turntable on top. A type 3 turntable can be used on the bottom for added rigidity over the type 2. 

Then there is the problem of the boom drive and possibly the cylinders tearing themselves apart under too high a load. Just for fun I put a 3 pound jar (roughly 1.3Kg) on the front boom of my BWE standard model and supported the central frame with one hand while operating the gear to actuate the cylinders with the other. They held on just fine so I'll move ahead with my own paired design cautiously and do another weight test after the current body revision is built.

Lots more learning about the model and possible Lego implementation has been going on, but I'm a bit stalled while trying to solve too many problems at the same time. Maybe I'll tackle the CVT first.