This may sound like a naive approach, but isn't the turntable overkill in this case?

Did you try a simple Technic pin peg to connect both parts if the robot, or do you actually need some transmission to go from one half to the other?

If a Technic peg isn't robust enough, maybe an axle would do the trick. I'd suggest using one Technic Axle 8 with Stop (), on which you first slide 3 regular Technic, Brick 1 x 2 with Hole () which will be attached to one half of your model, then 5 Technic, Brick 1 x 2 with Axle hole () which will be attached to the other. Maybe the strain on the axle will be too much (I read it's prone to breaking), but it could be worth trying.

And if that's not solid enough, build a staple of 2x2 round plates around an axle, fix that to one half of the model, and build a hole on the other half to have it slide in (a square hole is fine and easy to build: just a two bricks wide, two bricks high gap and you cover the studs underneath with a tile. Use archs if you want for the higher half, but don't bother for the bottom one). Of course you have to finish the pseudo-axle with something bigger than 2x2 to lock it in place.

And if THAT's not enough, there are 4x4 round plates now with which you could do the same.

This may sound like a naive approach, but isn't the turntable overkill in this case?

Did you try a simple Technic pin peg to connect both parts if the robot, or do you actually need some transmission to go from one half to the other?

If a Technic peg isn't robust enough, maybe an axle would do the trick. I'd suggest using one Technic Axle 8 with Stop (), on which you first slide 3 regular Technic, Brick 1 x 2 with Hole () which will be attached to one half of your model, then 5 Technic, Brick 1 x 2 with Axle hole () which will be attached to the other. Maybe the strain on the axle will be too much (I read it's prone to breaking), but it could be worth trying.

And if that's not solid enough, build a staple of 2x2 round plates around an axle, fix that to one half of the model, and build a hole on the other half to have it slide in (a square hole is fine and easy to build: just a two bricks wide, two bricks high gap and you cover the studs underneath with a tile. Use archs if you want for the higher half, but don't bother for the bottom one). Of course you have to finish the pseudo-axle with something bigger than 2x2 to lock it in place.

And if THAT's not enough, there are 4x4 round plates now with which you could do the same.