Thanks Hu / Al
What you say makes sense and I'll see if I can answer.
I previously decided to go stepper and have bought the driver card and software and so I am committed to an open system. Installing a servo with feedback control on the linear bearing makes perfect sense but .... not this time for me now.
So, being an open system means managing backlash which I want to do without having to resort to using stepper compensation but by keeping backlash out in the first instance.
I am driven by price and ease of construction and so I want to reduce the number of bearings and gears. I also want precision accuracy. My preference given those criteria was to use threaded rods (very cheap) and fixed at both ends (no bearings and easy to construct). I also like timing belts as there is minimal backlash. Given that design criteria, I am therefore committed to having the drive assembly actually on the gantry spinning a nut that when spun causes the gantry to move.
I can easily spin that nut using a simple timing belt pulley but that raises 2 problems for me.
1) I am cautious by nature and feel that gear reduction is required as I feel that gearing down will give me increased precision and control. I realise I will sacrifice feedrate but currently that is not important for me.
2) I have to replicate the assembly at the other end of the gantry to remove skew and therefore have to either use another threaded rod (cheap) or a very long timing belt (expensive and messy).
Given those problems, I would like to use a threaded rod with gear reduction. On the basis that I am employing simple gear reduction and as the two threaded rods at either end of the gantry are at right angles to the interconnecting threaded rod on the gantry, I was wondering if a worm drive might be the answer.
That was where my original question came from with respect to wondering if worm drives have an inherent backlash problem.
So, from the contributions I have got from this thread (thanks and thanks again) I feel that I have to now modify my design as worm drives seem too problematic. I think I now have two options shown below as A and B. Neither option should have any significant backlash issue.
The rack and pinion will be through a timing belt pulley and a timing belt laid flat and anchored at both ends. (Diagram B').
Andy
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