Different Servo Motors on One Machine

[mikkojay]

Hello All,
I am piecing a new gantry wood router together from my latest ebay scavenging. In doing so, it has got me leaning in the direction of eventually having a bit of variance in the chosen servos on the 3 axis (in size and voltage).
Since my previous machines have had identical motors on x,y,z so it feels a little odd in deviating from that, but the more I think about it, the duty, or about of work doled out by each axis, does seem to be spread out a bit unevenly.

Looking at the amount of force required to move each axis and the weight each is holding/pushing, here is my very unscientific/guess breakdown of the percentage of power required to move each axis:
X) 60% (needs to push/pull weight of Y and Z assemblies and gantry itself)
Y) 25% (needs to push/pull weight of Z assembly)
Z) 15 % (needs to push into material assisted by gravity/lift its own weight)
The above figures are a bit exaggerated, but illustrate my question-

Does anyone else run mismatched servo sizes on their machines?
I know it would be convenient to have them all be identical, but due to the recycling/scrap aspect of this machine, that might not happen- at least not for the first incarnation.

Thanks, Mike

[Al_The_Man]

??It is often rare to have all identical motor sizes on a machine, each have usually very different loads and acceleration rates?
Sometimes voltage variation between motors can require some changes especially when wanting to use a common supply, if supplies are separate, then it does not really matter?
Al.

[mikkojay]

Hey Al,
That's good it is more common than I assumed-
My Techno Isel had the exact same motor on all 3 axes, as well as the old mill I put together years ago (just because I happened to have 3 that matched). When I see "CNC XYZ motor kits", they (nearly) always advertise 3 identical motors. That is why I was stuck in that mindset. Breaking free from that is what felt odd at first.
Also, yes- I plan on having 2 power supplies. I have a 30v power supply that I am going to use for the Z driver and z brake. I also plan on a 70v power supply for the X axis (has a 60v MCG motor).
Follow up question- do you think that if my Y axis motor is rated for 38.2v that it would be streching it too far to run it from a 70v supply?
I see often a rule of thumb that says to use a supply that is rated at 150% the max voltage of your servo's voltage rating. I suppose I could just try it and see if it works- then if not, just get a bigger servo.

Thanks for the input, I appreciate it.
-Mike

[Al_The_Man]

70v for a 40v motor may be on the high side, it would mean your drive is going to operate in the 60% range to limit the rpm.
see Power-Supply Considerations For Servo Amplifiers
If these are linear supplies with toroidal transformers, you could easily remove turns to suit.
Al.

[mikkojay]

Excellent link- I will read and reread that one in detail tonight. I haven't bought the 70v supply yet, but the one I was eying is a toroid.
Thanks again- hopefully I'll have some more details to throw in a new machine build thread sometime soon
Thanks, Mike

[Al_The_Man]

Originally Posted by mikkojay but the one I was eying is a torroid.

Easy to mod, also if you need a small aux supply, just add an overwind.
Al.