I reckon they're both right :) Jonathan's calcs are ok if you are not microstepping cos then you have to derate the torque significantly not to lose steps, so Dean's answer is pragmatic in the likelihood you will be microstepping.
Personally I would still use two motors, but for other practical reasons - not due to the torque rating.
Last edited by Jonathan; 23-10-2014 at 09:01 AM.
I've just about reached the stage on my machine where I have to decide one motor/twin belts or two motors. Sounds like the received wisdom is to go two motors. So, that means buying one more motor, another driver - but the old analogue ones I have at present are obsolete, so that will mean two new digital drivers, and, what's worse, ditching LinuxCNC and having to use Windows/Mach3 to be able to home two motors, and, probably, an external motion controller. Ho hum...
They don't and can't take into account all the factors that make up a working machine. They don't account for miss alignment or poor materials and how machine is designed and built or the affect this as on friction etc.
They don't account for the affects of resonance. They don't account for Cheap drives running on PC with poor pulses from a ropey parallel port.
They don't account for the DIY affect and the numerous things that can affect how machine performs.
All these things come into play and have a big affect on the overall performance and the calculators can never know these variables so IMO they are only to be used as a very rough guide.
This particular case is a prime example because while the Calculators says 1 x 3Nm Nema23 turning 2 x 1300mm screws connected with belts should all be hunkydory I can tell you with confidence you won't get anything like the performance that as been suggested. Yes it will move them but at much slower feed rate and acceleration than the calculator suggests to give a stable working machine.
So Neil believe me your Not Erring on the side of caution your doing what's is needed to get the level of performance your looking for.!!
The single or Twin motor argumant falls down to ONE real differance.! . . How stable and accurate do you want your machine.?
If you wan't very stable with virtually no chance of screws losing sync even with cheap electronics then you need single motor/belts.
If you want to use twin screws then while they do work well they only do so provided certain things are correct.?
They are much more sensitive to motor tuning and need careful attention not to push too hard.
IME They work best and get best performance from them with Modern digital drives and External motion control cards which can provide nice clean pulses compared to ropey parallel port.
IMO it's crucial they have some form of stall detect or Error signal on the drives so if one motor stalls or drive fails the system shuts down. I won't build a twin screw machine without this option and Those that have built using twins motors and had this happen at speed will tell you how scary the big potential for damage.
I build more machines using Twin motors than single motors because it's easier but will ONLY do so provided I can build like the above. I Only build using Motion control cards and Digital drives and still leave a comfortable margin on tuning for best reliabilty and safety.
I never have any issues with twin screws building this way but it comes with a cost. Single motor and belts while more messy and involved is cheaper and more forgiving with lesser electronics.
I never truely trust twin screws not to stall or twist up the machine in some way if pushing hard for exteneded periods and I'm always mindfull while using and setting up. Where has I have complete trust in single motor setup and it never enters my head in use no matter how hard I push, no matter how long I push it for.!!
Last edited by JAZZCNC; 23-10-2014 at 02:14 PM.
The Following User Says Thank You to JAZZCNC For This Useful Post:
M = Misalignment
Q = Materials quality
D = Design and build
F = Friction etc.
R = Effects of resonance.
C = Cheap drives running on PC
P = Ropey parallel port.
Y = DIY effect
O = other miscelaneous effects
For each of the above assign a value between 0 and 1; 1 = 'perfect' or negligible, 0 = 'total shite'
JazzFactor = M*Q*D*F*R*C*P*Y*O
(Note: if any value=0 then JazzFactor=0 hence idea=total shite so don't even bother.
Actual calculation = theoretical calculation * JazzFactor
theoretical torque = 0.75Nm
JazzFactor = (0.9 * 0.95 * 0.9 * 0.99 * 0.9 * 0.95 * 0.9 * 0.85 * 0.85)
actual torque = 0.75 * 0.42
actual torque = 0.32 Nm
Last edited by EddyCurrent; 24-10-2014 at 08:21 AM.Spelling mistakes are not intentional, I only seem to see them some time after I've posted
Well I dusted off the frame this afternoon and took the last of the epoxy off. It's actually set really hard so I could have used it after all....but better safe than sorry I'm going to re - do it from scratch. 10 mins with a hammer and chisel (screwdriver) and and angle grinder with flapper disc and it's back to bare metal. Going to cut mdf sides this time and seal the gaps/edges/joins with silicone sealant. Got to do a bit more proper work now this afternoon on the lathe but hope to get the moat done tomorrow.
Video showing the hardness of the set Epoxy...
Last edited by njhussey; 18-12-2014 at 05:01 PM.
Only managed 1/2 hour on this today but cut the MDF for the moat. Tomorrow I'll glue it together and seal it, thinking of sticking it to the steel with silicone sealant which will also act as a sealant to stop (hopefully) any leaks as I don't want a repeat of last time where despite my best efforts (obviously not good enough) I had leaks at some joins.
If I can get it together and sealed then I might go for a pour so it starts to set over the weekend. Whatever happens I'll not be rushing this....lesson has been learnt from last time :)
I trust you read silyavski's thread about his epoxy method ?Spelling mistakes are not intentional, I only seem to see them some time after I've posted
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