Hi dlang!
I don’t have this setup and I’m unfamiliar with the problems you guys are having.
Can you please elaborate on the problems you encounter when the sled is high on the board?
I know as high the sled gets, the more force the motors need to keep pulling it up, as closer the sled is from the same height of the sprockets harder it is for the motors, to the point that the motors will be pulling against each other.
But if you add weight to the sled AND compensate it on the counterweight side, you’re not adding any extra load to the motors, besides the extra side load on the sprocket that i mentioned before.
Counterweights are used everywhere, it’s a simple and effective way to reduce loads, think of how a building elevator works. The weight of an empty elevator is compensated on the counterweight side, and the motor is only lifting the weight of the load in it (cargo, people, drag…).
In the case of the sled, the tension of the chain is never reduced, the sled still weights the same, chain still have the same tension and gravity still pulling it down the same way, the sprocket is the one that has to deal with the increased side weight due to the fact you are doubling the weight on it, but you are also reducing the force the motor need to lift the sled due to the counterweight, everything else still the same.
I have no experience with step motors, but since it is worm geared, how can it rotate in any direction without being commanded by motor side?
As I said before, just came across this wonderful project two days ago, so excuse my ignorance on this, unfortunately there are no kits for sale so I cannot experiment.