# Machsupport Forum

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

Title: question on weight
Post by: dude1 on September 08, 2013, 05:59:10 PM
need some help working out weight of a gantry to convert it to kgf-cm or kgf-m to N m.
the gantry weight is about 200 kg.
do i just do 200kg-m to Nm or is it 200kg-cm to Nm.
i know how to convert one to the other im not sure if i use 200kg-cm or 200kg-m to work out the conversion from 200kg to Nm
Title: Re: question on weight
Post by: RICH on September 09, 2013, 06:54:20 AM
daniellyall,

1 kgf-m = 9.80665 N-m

The above conversion is for force at a distance from some point which is a TORQUE value. A N-m 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
Title: Re: question on weight
Post by: dude1 on September 10, 2013, 05:33:01 PM
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
Title: Re: question on weight
Post by: RICH on September 11, 2013, 05:54:53 AM
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

Title: Re: question on weight
Post by: dude1 on September 11, 2013, 06:45:19 PM
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.
Title: Re: question on weight
Post by: dude1 on September 11, 2013, 07:15:38 PM
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
Title: Re: question on weight
Post by: dude1 on September 11, 2013, 07:41:45 PM
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 oz-in  not the 800oz-in 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 1288oz-in stepper motor at 72v it should out put around 900 oz-in what should work fine if all calcatlations are correct.
Title: Re: question on weight
Post by: BR549 on September 11, 2013, 10:02:53 PM
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
Title: Re: question on weight
Post by: dude1 on September 11, 2013, 10:04:14 PM
how cant find info i this i can understand
Title: Re: question on weight
Post by: RICH on September 12, 2013, 06:30:30 AM
Attach the motor curve you are using.

RICH
Title: Re: question on weight
Post by: RICH on September 12, 2013, 06:32:54 AM
Attach the motor curve you are using.

RICH
Title: Re: question on weight
Post by: BR549 on September 12, 2013, 10:31:34 AM
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
Title: Re: question on weight
Post by: BR549 on September 12, 2013, 10:47:23 AM
AND a second reference

http://www.techno-isel.com/Tic/H834/PDF/H834P009.pdf

(;-) TP