# Precision of a steeper motor and gears vs multiple motors

We are a student team trying to design a low cost CNC plasma cutting machine. The CNC will be a table with two rails and a bridge moving on them in which the head of the plasma torch will be.

Now we have to decide on the configuration of the steeper motors to move the bridge. It has to be pushed from each end of it, we have tought about:

• Two motors, one on each end of the bridge.
• One bigger motor in one end (or the middle) and a mechanical transmission (a shaft and a couple of gears) to push from the other end.

Given that the small motors cost about $15 each and assuming the big one is double the price, mass, torque, etc, what option would give the most precision with an acceptable cost? Shaft would be a metal rod, but I dont know how much money could be precise enough gears. EDIT 1: We finally went for double motors. As the project is aimed at managing the project itself and setting up a production chain, and not at designing a good product, we didn't think much about the pros and cons, and thought that just doing two of the same was less work than designing the mechanical transmission and its production and assembly process. • Have you looked how these are made? Downloaded plans for making cheap 3d printers? Oct 6 '20 at 13:55 • You should really define a target precision or target cost, then work backwards from there. An acceptable cost for NASA is different than a autobody shop. How "low" is low cost for you? 50 dollars? 50,000 dollars? Second @solarmike look around at how existing machines are designed and see what advantages/disadvantages their layouts have – jko Oct 6 '20 at 15:18 • @jko so you include me to make similar points to me... my son made an adjustable gate for a flume using a single motor with fine control, gears and toothed wheels & belt... Oct 6 '20 at 16:22 • @SolarMike We looked at some designs but found little explanations. Oct 12 '20 at 17:33 • @jko The target production price would be about 2000€ /$2400. Aimed at small machineshops mainly. Oct 12 '20 at 17:37

If you are looking to move the whole bridge (gantry might be a better term), and size of the length of the gantry is more that a couple tenths of a meter (>0.3[m]), then using a large motor with gear is not going to be economic at all.

With a single motor your only viable solution might be a synchro belt, or a chain.

Having two motors will probably be more easy to go.

For other issues that might crop up you can have a look at this question also