[Falcon69]

Okay, here's what I have for a build, and after reading alot on how to calculate stepper motor, I'm still confused. Math is just not my fortay.

Anyway, Here's what I'm planning on building...

4'x8' router which will have the following:

• 25mm profile rails and blocks on Y-Axis (1 on right side, 1 on left side, with 2 blocks on each)
• 20mm profile rails and blocks on X-Axis (1 on top, 1 on bottom, 2 blocks on each)
• 2:1 reduction pulley system on X-Axis and Y-Axis (purchased from CNC Router Parts)
• Rack & Pinion on X-Axis and Y-Axis (20mm Pitch)
• 16mm ballscrew for Z-Axis (1605 I think for better accuracy unless you think I should go with a 1610)
• 20mm diameter rails with blocks for Z-Axis
• Z-Axis will be direct Drive with a Coupler connecting the motor to the ballscrew
• Table will have two Rack and Pinions and Motors, one on each side to help prevent racking.
• Gecko 203 Drives (or maybe 210 or 213 if better?)

The question i have, is, what size motors to use? Someone mentioned a 640 oz. Nema 34 in another thread. Okay, but should I buy four of that size, or X-Axis (x1), Y-Axis (x2), and Z-Axis (x1) should be different size? And, what do I look for on eBay when purchasing? How many Amps? 1.8 degree? Torque Rating?

Also, I would need x4 Geckdrives, and a seperate Breakout board, correct?

How big of a power supply? I'm assuming a 48volt one. From looking at the different ones on eBay, they have 3 +v and 3 -v outputs. So should I get like two (for example) 400watt ones? what amps? 7.5A? 12.5A?

I will also be running a SuperPID to control the router speedle of the Porter-Cable 7518 Router. So I need to purchase a seperate Power Supply for that? What voltage and power rating?

I want to try and purchase all the rails and electronics this weekend, so your advice and reply's are much appreciated.

I have the skills to build this thing, but I don't have the brains (yet) for the calculations.

The gantry will weigh close to 210lbs., with the motors , profile rails, blocks, Z-Axis, ballscrew, rails, and the rack & Pinion set-ups.

The Z_Axis will weigh about 45 lbs. with the router and stuff.

My idea is to cut mostly plastics, PVC, ABS, Polycarbonate, Etc. There will be some cutting of wood and Aluminum. So, I'm guessing when calculating, the strongest applied cutting force would be for the Aluminum, though, I'm not sure how to calculate that.

I would like to see my rapids better than 1000IPM. But, I don't want anything to fast that it would move the table when the gantry stops.

You can see my build here to get an idea of how solid I plan to build it. Falcon's 4ft x 8ft. CNC Router Build

So, what size motors should I be buying?

Please help if you can. If you need more info, message me or post here. I'll check it often.

Also, I'm going to purchase the computer too. Motherboards now-days are hard to find with a LPT port. Would using a PCI card with the LPT port work okay? Not sure on the software, but I'm guessing MACH 3 is what I'll use, since alot of people are using it.

[KOC62]

I have limited experience with CNC. However some of your questions need to be answered in a certain order.
For example, you shouldn't, in my opinion, order a power supply until you know what motors you are getting. You shouldn't order a stepper controller until you know what motor size (power) you are buying. One decision affects the other.

Since your gantry weight is heavier than I am, I'm thinking of what kind of power does it take to move me at 1000 IPM then suddenly stop me and then change directions? Without math we don't know. Experience might.

Are there other successful builds of your type and weight? Then use their selection of steppers for a start. Sound engineering is not throwing parts together without a good understanding of each part.

An experienced cncer's answer might be quicker, but in the meantime;
Selecting the Proper Size Stepper Motor - Developer Zone - National Instruments This article does require input of data for its math. I don't have your numbers to input.

[Falcon69]

For example, you shouldn't, in my opinion, order a power supply until you know what motors you are getting. You shouldn't order a stepper controller until you know what motor size (power) you are buying. One decision affects the other.

This I understand, that's why I'm here. I know what I want to do with the machine, I know the weights of things.

What I don't know is how to do the calculations. And I know from reading the threads on this site that NEMA 34 motors are what I need (However, Nema 23 will work, but not idea).

I've seen that site you linked, and many others, but it's all greek to me. I'm not very good in math and have no idea what information the formulas are requesting.

I've even tried using the nice worksheet they have on Oriental Motor site. I don't understand what is being asked.



These are what they ask for:

• Weight of Load (W1) = ____ lb
• Friction Coeffeicient of the Guide (µ) = ____ (0.5, 1, 3, 5)
• Rack Weight Rack Mass (W2) = ____ lb/pc
• Pinion Pitch Diameter (DP) = _____ in
• Pinion Pitch Weight (WP) = ____ lb/pc
• System Efficiency (ƞ) = ____ %
• External Force (FA) = ____ lb
• Primary Gear Pulley (Gear) Pitch Circle Diameter (PCD) or Diameter (Dp1) = ____ in
• Primary Pulley (Gear) Weight (WP1) = ____ lb
• Secondary Pulley (Gear) Pitch Circle Diameter (PCD) or Diameter (DP2) = ____ in
• Secondary Pulley (Gear) Weight (WP2) = ____ lb
• Mechanism Angle (α) = ____ °
• Stopping Accuracy (Δ|) = ±____ in
• Safety Factor ____ (1.5, 1.75, or 2)

It also asks for:

Fixed speed operation: Operating Speed (V1) = ____ in/sec

OR

Variable Speed Operation : Operating Speed (V1) = ____ in/sec ~ (V2) = ____ in/sec

OR

Positioning Operation: Rotor Inertia (JO) = ____ oz-in²
Gear Ratio (i) = ____

Where do I find these values?

[ger21]

I'd ask CNC RouterParts what they recommend for their components.
Since they sell both 640 and 960 oz motors, either should work.

Voltage is dictated by the specs of the motors.
If you go with the 640oz motors, you don't want more than a 36V power supply.

The max voltage should be 32 times the square root of the motors inductance.

You can probably use a smaller motor for the Z axis, but it's easier to just use the same size for all. Otherwise you might need different power supplies.

Yes, 4 Geckos, and a breakout board.

The SuperPID just needs 5V, which you can take from the PC.

[KOC62]

Falcon69

I can empathize with you. I too had all these questions. But I also know from my electronic background that you just can't design something for someone else on a forum like this. It takes a fair amount of homework that someone has to do. The answers to the questions that were asked is the "homework" part. Since many here don't have engineering training, many of the questions is "greek". Unless an experienced user has done all the experimental part of a similar machine, you can't expect anyone to know exactly what you need to do. We give guidelines from what we know based on our limited experience.
But we try to help where we can.

[Falcon69]

okay, so if the motor specs say mH is 6.8, that's √6.8*32=83.45

So that motors idea Voltage rating is 83 volts?


This is a 640oz. motor from Kelingc.net that has 4.5A

Now, other motors on Ebay say 2A. I'm confused, they all look the same. SO are the other motors basing there's off 2A * 2-phase? so it would be a total of 4A?

[ger21]

okay, so if the motor specs say mH is 6.8, that's √6.8*32=83.45

Yes.

All current ratings are per phase.

The Ebay sellers sell 2 amp motors so they can use them with their cheap chinese drives, which only supply 2.53 amps. But, they don't perform very well.

The motors from CNC Router Parts are 7 amps, with very low inductance. The downside is you need to use drives that can provide the 7 amps, which usually means Geckos. You'll also need a higher current power supply.

Generally, the lower inductance, higher current drives are capable of spinning much faster and have much more torque at higher speeds.

If you only need the motors to spin 300rpm, though, it doesn't make a lot of difference which motors you use.

[Falcon69]

Thank you Gerry, You answered my next question on difference of amps in motors.

That makes alot of sense, I'll be ordering the motors from CNCRouterparts then.

So, would I be better off ordering 3x 960oz. motors and 1x 640oz motor (for z_axis), or just get all 960oz, or all 640oz?

It seems you're right about the 640oz only having a max powersupply of 36volts. However, on CNC Routerparts website, they are selling the motors with their 48v 21A powersupply. It seems with the calculation that the 960oz motors can handle up to a 53volt input.

So, for my application, 960oz motors or 640oz?

And what type of power supply? 7A per motor x4 = 28A

640oz draws 252 watts at 36 volts
960oz draws 336 watts at 48 volts.

So, I would need a 808watt 36volt 28A power supply if I go with all 640oz?
Or, I would need a 1344 watt 48volt 28A power supply if I go with all 960oz?

[ger21]

It seems you're right about the 640oz only having a max powersupply of 36volts. However, on CNC Routerparts website, they are selling the motors with their 48v 21A powersupply

According to Gecko, 36V is all you need, and anything more will only cause excessive heating.

For amps, you need 2/3*7 for each motor, or about 4.66 amps. Call it 20 amps for 4 motors.

So, for my application, 960oz motors or 640oz?

Since I have no experience with any of the components in question, I'm not even going to attempt to guess.

[Falcon69]

okay, figured out the amp thing. 2/3 rating on power supply for total of all motors. so, 28A*(2/3) = about 18.7A.

K, so that's the amount of Amperage I need for power supply. Still gotta figure out the Watt.

[Falcon69]

Okay, I'm just going to buy the Power Supply that CNC Router Parts has, allthough, I think it's alittle expensive.

So, if I get all 960oz motors versus 640oz, what's the worse that can happen? Will I not be able to reach my rapid speeds of 1000+? Will I not be slow enough for cutting Aluminum?

I just don't want to purchase the smaller ones, then find out later I need the bigger ones. Money isn't really that much in difference, so is not a problem.

Advantage of going a higher motor vs. smaller motor (torque) ?
Disadvantage of going a higher motor vs. smaller motor (torque) ?

Again, thanks for everyone's help.

[ger21]

In some cases, larger motors can be slower. I don't think it will be an issue in this instance.

[Falcon69]

okay, thank you Gerry.

I'll go ahead and buy them now then. thank you!

[Falcon69]

$240 seems alittle high for that 48v power supply.

Could I get away with running four 48v 350watt 7.3A (or even 5A i think will work for those 7A motors) Power Supplies bought from Ebay? It's like $100 cheaper doing it that way.

[ger21]

I'd probably go for this one.
Unregulated Linear 1000W/50VDC/20A Toroidal PSU (KL-5020) | | Automation Technology Inc Automation Technology Inc

[Falcon69]

awesome! Thank you. SO I just wire the motors to the gecko drivers, then wire those parellel into this one power supply?

[lgalla]

Hay Fal I am pretty bad at math as you.Here is a motor size formula in watts from Gecko that is simple....


Q.) Should I use servos or steppers in my machine?

A.) If you are designing a machine and you get to motors, the first thing you should do is calculate the power you need. Never buy a motor (stepper or servo) first and then figure out if it will fit what you need.

Motors are motors. They couple power to your mechanism and power is what makes things happen. The choice of a motor comes after you know what's needed.

Power is velocity times force or torque times RPM. It doesn't matter if the motors are steppers, servos or a gerbil in a spinning squirrel cage at the start.

To separate what motor need (neglect the gerbil), is the power your mechanism needs.

Rule #1: If you need 100 Watts or less, use a step motor. If you need 200 Watts or more, you must use a servo. In between, either will do.

So, how do you figure the power you need?

Method 1: You have a plasma table, wood router or some other low work-load mechanism. You have a clear idea of how many IPM you want but you’re not sure of what force you want at that speed.

Pick the weight of the heaviest item you are pushing around. If it weighs 40lbs, use 40lbs. multiply it by the IPM you want. Say that's 1,000 IPM. Divide the result by the magic number "531". The answer is 75.3 Watts so use a step motor.

Eq: Watts = IPM * Lbs / 531