Machsupport Forum
Mach Discussion => General Mach Discussion => Topic started by: dude1 on September 08, 2013, 05:59:10 PM

need some help working out weight of a gantry to convert it to kgfcm or kgfm to N m.
the gantry weight is about 200 kg.
do i just do 200kgm to Nm or is it 200kgcm to Nm.
i know how to convert one to the other im not sure if i use 200kgcm or 200kgm to work out the conversion from 200kg to Nm

daniellyall,
1 kgfm = 9.80665 Nm
The above conversion is for force at a distance from some point which is a TORQUE value. A Nm is used to provide
motor info....usualy.
You don't have a turning force from the weight until you calculate the force required to just move the weight along
a path. That force, refined .....based on gearing, friction factor and screw / gear / belt influence, times the offset distance to the driving
axis will give you a torque value.
RICH

the nuts and bolts of it is, pin pully 90 tooth, stepper pully 18 tooth, the rack pitch is 3.78 the pin is 23 tooth the axis can move 2.4m. i cant under stand the formullars for working out the required forces, im bad at math

Most of the major motor / rail / screw suppliers provide sizing software on their web sites to do the calculations for you based on supplied information of your sysytem. Do a search and try some of them as they all do the same but the input interfaces are different. The result
can be used as a guide for intial selecton of components. I say guide because it provides a theoretical value and one still needs to
use some common sense on how conservative they want to be on sizing.
There is a practical way.
Once you build your system, ADJUST / LUBRICATE IT, but before you purchase motors, find the the torque to just move the axis by measuring it. Just use a torque wrench (or an equivilant like hung weights) to find the value. Then double or triple the value. Be consrvative
as this allows for acceleration at higher motor rpm values ( remember that a steppers torque decreases as rpm increases ) and a servo is sized differently.
There is nothing wrong with comparing equivilant size equipment to get a quick ballpark figure. But do make note of YOUR desired
operating conditions.
Designing a system can get complex quickly and one needs to understand what they are doing.
So, you intial question is a loaded one, and hope replied information helps you out.
RICH

i have been trying to work it out its on r an p i am have trouble working out the pitch of the rack i counted 50 tooth it was 189 mm long, when i work it out its wrong i used a ball screw calculator and worked out the pitch is 300 to get the same steps/per as what the machine is out putting when it is calibrated.
if some one has a good formular to work it out help.
i have attached a copy of the step cala i used to work it out.

i have been trying to work it out its on r an p i am have trouble working out the pitch of the rack i counted 50 tooth it was 189 mm long, when i work it out its wrong i used a ball screw calculator and worked out the pitch is 300 to get the same steps/per as what the machine is out putting when it is calibrated.
if some one has a good formular to work it out help.
i have attached a copy of the step cala i used to work it out.
its wrong its a pitch of 40 to get it correct i checked it of against the axis that i have with a ball screw so 40 is correct for pitch

this is correct this time had someone else look at it :[
thanks rick i have just finished doing that it works out that the stepper is doing 187 rpm it should easly do 2400mm/min but only can do 800mm/min max in acurucy going faster than 800mm/min its just *********. had a look at the torque vs speed chart it shows the motor this machine has will be running at about 500 ozin not the 800ozin it is ment to be out putting thats useing a stepper calcalator that works out the rpm as well as steps/per this version is correct can someone check please. if its correct going by the weight of the gantry running a 1288ozin stepper motor at 72v it should out put around 900 ozin what should work fine if all calcatlations are correct.

What you need to calculate for is the torque required to accellerate the mass at the level you require. It is an inertial calculation.
Just a thought, (;) TP

how cant find info i this i can understand

Attach the motor curve you are using.
RICH

Attach the motor curve you are using.
RICH

This should get you started look at the tangent drive calcs it is what a rack and pinion setup is.
http://www.baldor.com/pdf/brochures/br1202_1_02_sectj.pdf
(;) TP

AND a second reference
http://www.technoisel.com/Tic/H834/PDF/H834P009.pdf
(;) TP