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Author Topic: Calculating What kind of power i need for rack and pinion 4x8 table  (Read 9564 times)

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Offline eloid

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can someone look this over i think i may have a error here,
Im planing to use dual drive motor on my x axis with rack and pinion set up
5x9 table.

how does that change this calculation...

rack
S1811Y-RB-1P
24 diametrial pitch 20° pressure angele

Pinion gear = 1” in diameter
One rotation = 1 * pi (3.141) = 3.141 in travel per rotation
Target rapid transverse = 1300 ipm

NEMA 34 HIGH TORQUE STEPPER MOTOR 1810 oz-in,
http://www.kelinginc.net/SMotorstock.html
RPM of pinion to achieve rapid transverse = 1300 / 3.141 = 413.88 ~ 414 rpm
Estimate stepper RPM = 3000 rpm
Required reduction ratio = 3000 / 414= 7.24:1 ratio
Available peak servo torque = 1810 oz-in
Torque output of reduction gearbox = 1810* 7.2 = 13032 oz-in
Torque at radius of pinion gear = 13032/ (7.2 / 2)
.........................................= 13032/ 3.6 = 3620 N

Acceleration = F = m * a

Available peak force at pinion radius = 3620 N

Estimated mass of gantry = ~150 lbs

3620 = 150 * ?
= 3620 / 150
= 24.133 ipm

Target rapid transverse = 1300ipm
Time to achieve rapid transverse = 1300 / 24.133 = 53.86 sec

how do i calculate my resolution?

Offline docltf

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Re: Calculating What kind of power i need for rack and pinion 4x8 table
« Reply #1 on: November 14, 2007, 12:04:37 AM »
looked up the torque and speed for your motor at the keling site.at 1000 rpm motor strength is 1/10 of the rated value.I do not believe you will ever see 3000 rpm.

Offline DAlgie

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Re: Calculating What kind of power i need for rack and pinion 4x8 table
« Reply #2 on: November 15, 2007, 09:59:43 PM »
I have essentially this machine you have. It will rapid at those speeds, but with motors about half the size you have. Note that voltage is your friend when you need power with steppers, mine runs at 90 volts. Mine has some reduction before the rack, I have never counted teeth on the belt drive but would estimate it to be 10:1 reduction. I think that you will get what you want with those huge motors if you have maybe 70 volts feed to them. Apples to apples engineering you know....
               DaveA.

Offline Whacko

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Re: Calculating What kind of power i need for rack and pinion 4x8 table
« Reply #3 on: November 16, 2007, 01:08:47 PM »
What is the impedance of your motor windings? Low impedance high voltage adaptive drivers gives you high motor speeds, but you must be carefull not to overheat the motors, as that destroys the magnetic armature for good. High speed gives huge eddy currents as the current is also recycled in the off period of the pwm. That translates to temperature rise. I've hammered a nema 23 motor to beyond its capabilities just for fun. I was impressed. I got close to 3000 rpm with some reasonable torque, but I must add that it is on a 400V 16A adaptive drive. The current was limited to 4.65A and the motor was supplied by USDigital. The armature is now demagnatised, and I now call it a BLDC motor. (Brushless DC motor)

Whacko for destruction ;D
Nothing's impossible
Re: Calculating What kind of power i need for rack and pinion 4x8 table
« Reply #4 on: November 16, 2007, 08:04:34 PM »
Eloid,

You really need  a proper maths expert to answer all your questions but I'll have a try and then they can shoot me down.
"Pinion gear = 1” in diameter"
Gears operate on their pitch circle diameter (PCD) . A 24DP 1.00 inch OD gear has a PCD of 0.917ins.

"Estimate stepper RPM = 3000 rpm"
DAlgie and Docltf are giving you good advice. At 3,000 there is not much torque available. Is there enough to drive your gantry? 80-90 Volts and a good driver will give usefull torque up to maybe 2,000 rpm if your slide are low friction you should be OK. Don't be tempted by Whacko's 400V - it only lets out the magic smoke!!

"3620 = 150 * ?
= 3620 / 150
= 24.133 ipm"

You are mixing units here stay with metric or imperial. Acceleration should be in inches/sec/sec and you can set this in Mach3 so that the stepper does not stall running up to your target speed.

"Target rapid transverse = 1300ipm" 
200 ipm would be more realistic with your steppers. It depends on torque available. Factors that rob you of torque include - motor detent torque, friction and the inertia of your gantry. If you want real torque at speed you need servos.

Time to achieve rapid transverse = 1300 / 24.133 = 53.86 sec

Formula you need is v=at . Final velocity = Acceleration X Time applied.

how do i calculate my resolution?

Your resolution will depend on several constants - reduction gearing, how many microsteps from the driver and is your computer powerfull enough to drive Mach3 at 100kHz kernel speed. Answering these will give you resolution in steps/inch for your table travel.

There you go, at least I have tried to help you along but I am not an Expert. Where are you all?

Ian



Ian