theory on lead screws/stepper motors etc

[monkeyturnip]

assuming everythnig being perfect, no backlash/slop/play in the motor, screw, nut and the weight of the gantry being 1kg, and the motor running at 1rpm

just checking my maths but if i get a stepper motor with a 1.8 degree step it will take 200 steps for a 360 degree rotation.

if i connect that to a acme lead screw with a 5mm pitch that will move the nut 5mm for every 360 degree rotation = 200 steps

the nut will move 0.00025mm per step

if the bed is 1000mm long it will take 40,000 steps to go from one end to the other = 200 360degree rotations on the screw/motor

= 200 (3 hours 20 mins) mintues for it to move the nut from one end to the other

i was doing this to try and work out the formula for torque, i would then adjust the variables to calculate the torque of the motor required, to make sure i didnt under or massivly over specify/purchase but i cant get my head round that part

[ger21]

Originally Posted by monkeyturnip assuming everythnig being perfect, no backlash/slop/play in the motor, screw, nut and the weight of the gantry being 1kg, and the motor running at 1rpm just checking my maths but if i get a stepper motor with a 1.8 degree step it will take 200 steps for a 360 degree rotation. if i connect that to a acme lead screw with a 5mm pitch that will move the nut 5mm for every 360 degree rotation = 200 steps the nut will move 0.00025mm per step if the bed is 1000mm long it will take 40,000 steps to go from one end to the other = 200 360degree rotations on the screw/motor = 200 (3 hours 20 mins) minutes for it to move the nut from one end to the other i was doing this to try and work out the formula for torque, i would then adjust the variables to calculate the torque of the motor required, to make sure i didnt under or massivly over specify/purchase but i cant get my head round that part

What exactly is the question?

[monkeyturnip]

Originally Posted by ger21 What exactly is the question?

oh yeah i forgot to put that

origionally that was just cheking i was correct with my maths and that i was barking up the right tree.

basically im trying to work out all the forces involved with making my router, so i can calculate the thickness and type of the materials for the base, gantry etc, the size of steppers needed, as apposed to blindly buying parts and hoping they arnt under spec, or spending money needlessly on over spec parts thus wasting money.

im having trouble calculating the maximum torque the motors will encounter, and then i can translate this into the forces the different parts of the machine will encounter to get the type and thickness of material for the other parts, i also want to factor in (later in the clacs) minimising vibration etc

[pminmo]

Originally Posted by monkeyturnip assuming everythnig being perfect, no backlash/slop/play in the motor, screw, nut and the weight of the gantry being 1kg, and the motor running at 1rpm just checking my maths but if i get a stepper motor with a 1.8 degree step it will take 200 steps for a 360 degree rotation. if i connect that to a acme lead screw with a 5mm pitch that will move the nut 5mm for every 360 degree rotation = 200 steps the nut will move 0.00025mm per step if the bed is 1000mm long it will take 40,000 steps to go from one end to the other = 200 360degree rotations on the screw/motor = 200 (3 hours 20 mins) mintues for it to move the nut from one end to the other

Maybe my brain is foggy this morning, but I come up with one different figure. Yes, a 1.8 degree stepper at full step will have 200 steps per rotation/360 degrees. With a 5mm pitch screw one rotation will move 5mm, divide that by 200 (number of full steps per rotation) you will move .025 mm per step not .00025mm per step. A 1000mm bed would take 200 rotations with a 5mm pitch screw. At full step then you would need 200 rotations * 200 steps or 40,000 steps. At 1 rpm, you would need 200 minutes (3 hours 20 minutes) to move the full length.

BTW, 1rpm is really really slow, are you doing something you need slowness?

[monkeyturnip]

Originally Posted by pminmo Maybe my brain is foggy this morning, but I come up with one different figure. Yes, a 1.8 degree stepper at full step will have 200 steps per rotation/360 degrees. With a 5mm pitch screw one rotation will move 5mm, divide that by 200 (number of full steps per rotation) you will move .025 mm per step not .00025mm per step. A 1000mm bed would take 200 rotations with a 5mm pitch screw. At full step then you would need 200 rotations * 200 steps or 40,000 steps. At 1 rpm, you would need 200 minutes (3 hours 20 minutes) to move the full length. BTW, 1rpm is really really slow, are you doing something you need slowness?

just realised what i didn i divied 200 by 0.05m then x 1000mm as aposed to 1m if that maes sence

im using 1rpm as 1 is an easy number to work with at the mo to refine my calculations, then i'll change it to its true rpm when i know my maths work

[Oldmanandhistoy]

Hi,

Just wanted to say it’s nice to see you’re taking this approach to building a machine and not just second guessing.

Time taken to do the maths will save you a lot of time, money and headaches. I will look out for your build log it should make good reading (hopefully you will be doing one).

Good luck,
John

[pminmo]

You might want to look at this to help you also: http://pminmo.com/PMinMOwiki/index.p...chanical_Power

[monkeyturnip]

John cheers, ive made some expensive mistakes before by using my or others gut instincts and i try to not make those mistakes again, plus i like doing research and learning new things. this might sound arogant but i know i can build a CNC router, it would have its way over spec and parts way under spec, but building it right is the challenge, and knowing for sure that it will be able ot do the job i designed it for.

Pminmo thats a cool site you have there, lots of information, cheers thats some bed time reading

[Oldmanandhistoy]

Hope you are prepared for lots of searching
If there's anything you are having trouble finding information on, post here and I will try to point you in the right direction.

John

[monkeyturnip]

yeah alot of searching has been done, and alot more to be done, but its keeping me out of the way of my G/F LOL

cheers John for the offer