calculating size of stepper

[rofuth]

Hi everyone, this is a great place. Does anyone know the right way to calculate what size stepper motor I need. I am putting my list together for my 4x8 router together but want to verify the size of the stepper motors. the gantry will be 5' wide, running on 35mm thk rails for the distance of 8'. It will be a u shaped table so the 2 x 6 gantry should be surdy. It will be rack & pinion with a 3:1 ruduction/ spring loaded. I'm looking at the rs34-1840 but don't want to be to big. thanks for any help.

[Robin Hewitt]

You want a motor that can achieve the velocity you require and still maintain the required force to push the cutter through whatever you are cutting. If the motor can go faster without the torque dropping away then you can trade cutting force for speed and get a fast reposition/home movement between cuts.

Find a motor and look at the graph of speed against torque. The torque will usually fade away gently as speed increases then suddenly plummet. You want to work in the bit before the plummet.

Motors usually come with several graphs to show how they perform with different voltage/current combinations and also whether the coils are connected in series or parallel. Check out whether your requirement means an expensive power supply/driver combination, just because the motor can do it doesn't necessarily mean it is your best choice.

Hopefully your software allows you to program an acceleration so you don't have to worry about getting it up to speed, presume you will keep the rolling resistance low.

Good luck