Thanks m_c

I'm finding it hard to keep the weight down with an epoxy granite filled steel gantry of a suitably rigid shape.

I'm probably over compensating quite a bit. I'm going to try and bring the weight down.

I'm also failing to understand how to calculate which motor I'll need for a given linear system.

I'm basing the servo on Boyan's massive purple machine. Which I believe used a 400w servo for a 120kg gantry.