[samualt]

I take it the Gecko G320 is limited to only 20A: "0 to 20A current limit adjust range".
I'm guessing that means I can never reach my theoretical maximum of 1500 oz-in with the following drives:

Reliance Electric DC Brushed Servo Motors, Model E712
37.51 Oz-In/A
25.0-30.5 V/KRpm
Motor Terminal Resistance .75-1.02 Ohms @ 4A.
Maximum Terminal Voltage 60V
Maximum Continuous Speed 2100 RPM (No Load)
Maximum Peak Torque 1500 Oz-In.
Maximum Peak Current 44.5A
Maximum Continuous Stall Torque At Max Motor Temp 300 Oz-In.
Maximum Continuous Current 8.9A

Is there any way around that? Or, should I just not worry about that at all?
Also, does anyone here have any experience with these motors? Will the encoder that comes with them work with the Gecko?

[kong]

Rutex offer some drives that run upto 40Amp motors, but they are twice the price of the geckos. You must be planning one big machine to want 1500 oz/in?!
edit - just a thought, if you could run them at 20Amp, losing half the torque, you could run them on a reduction pulley, halving their speed, but boosting your torque back up. Obviously you'd need to go for a course ballscrew to regain the speed loss.

[HuFlungDung]

Samualt,

I wouldn't get too distracted by the big numbers of max peak torque and peak current. Those are design limit parameters, not optimum running conditions.

The motors will stand 9 amps continuous at 60 volts, so that is what you need, plus a little reserve. If the power supply has a capacitor or two, it may give you the capacity for the peak surges, which are only momentary conditions.

[balsaman]

I am with Hu. 10 amps at 60 volts is close to 2 HP. That's a whack of power.

Kong,

Using a 2:1 reduction and then using half the pitch is mechanically the same as twice the pitch and no reduction.

Eric

[ToyMaker]

At 746 Watts per horsepower, 10A x 60V is a little shy of 1 hp.
Which is still a healthy amount of power.

robotic regards,

Tom

[HuFlungDung]

Yup, you can easily break off a 3/4" endmill with 1/2 hp twisting on your screw.

[samualt]

Hmm...I'm still a little confused.
The Gecko's say no more than 20A.
So, do I build one power supply for all three motors? If so, what Amps should it output (because its going to 3 motors)?

Do I build a single power supply at 60V @ 60A (for all three motors)?
Or, should each motor have its own 60V @ 20A power supply?

[ToyMaker]

samault:
three 60v20a pwr sups might be cheaper than 1 60/60 but you will have to shop and see what's available.
speaking of high current supplies, what kind of voltage does a small (<100A) cracker-box welder put out?

robotic regards,

Tom

[HuFlungDung]

Originally posted by samualt
Hmm...I'm still a little confused.
The Gecko's say no more than 20A.
So, do I build one power supply for all three motors? If so, what Amps should it output (because its going to 3 motors)?

Do I build a single power supply at 60V @ 60A (for all three motors)?
Or, should each motor have its own 60V @ 20A power supply?

Neither: one 30amp/60V supply should do.

Chances are slim that you are going to be pushing all three motors that hard at once, depending on whether you want jack-rabbit acceleration, or not.

FYI, I've run Knee mills for years with 12 amp servomotors, and never had a trip out because I was using all three axis at once. Most of the time, the motors have it pretty easy, and are barely warm to touch. The Z axis gets the most workout, if drilling a few hundred deep holes on a peck cycle. My entire controller package runs off a simple 15 amp, 110volt circuit, and I've never tripped a main breaker yet.

[balsaman]

Originally posted by ToyMaker
At 746 Watts per horsepower, 10A x 60V is a little shy of 1 hp.
Which is still a healthy amount of power.

robotic regards,

Tom

You are correct, my quick math was a little too quick...

Eric

[turmite]

samault may I ask a question here that is real close to what you are needing? I don't want to hi-jack your thread.
turmite

[samualt]

turmite:
Hi-jack away! I don't mind. Really!
I think I have a good idea of what to look for now (I wonder where I can find some of those time-sequential dilithium warp-field amplifiers though? ;-)

[turmite]

Thanks samault. Ok guys here is my motor specs and the rpm spec the fellow I got these from sent me. Rpm first.


The motors will go 15 RPM for every volt applied.
At 60 volts, that is 900 RPM.

Reliance Electric DC Servo motor
Micro 100 Series
NEMA 34 Frame
Model 0675-03-018
Back EMF Constant, ke = 68 V/kRPM
Torque Constant, kt = 5.75 lb-In/Amp WOW!
That's PER Amp of motor current.
At just 10 amps, that's 57.5 Lb-In = 920 Oz-In.
Rated Peak Torque: 1080 Oz-In

Can you give me the formulas as to how these #'s were arrived at?

I want to move a 200# load at 300 ipm. This includes the weight of the load plus the resistance load of the cutter at full cut. At 900 rpm using a .200 pitch double nut ballscrew with a dia of 1.125, how do I figure the step up/down using timing belts and pulleys.

What kind and size of ps or multiple ps would I need to use to be able to achive my carving speed of 300 ipm. Could I also use the same ps to supply power to a stepper driver and step motor?

That ought to about do it. Thanks in advance.

turmite

[turmite]

BTT Hi guys. I was hoping someone could give me a little help/advise.

turmite

[turmite]

and again

[kong]

Your ballscrew would run at 900/5 IPM = 180 IPM, so to get to your desired 300 IPM, you would need to run a ratio of 180:300 or 18:30 or 9:15 which is motor:leadscrew.

[HuFlungDung]

Turmite,

Do you really need 300 ipm feedrate, or is this your rapid traverse rate?

It takes lots of fancy software and a fancy controller to actually control a machine accurately at that feedrate. Talk to Hardmill

[turmite]

Thanks kong. I still need to know about the stepper using the same power supply as the servos plus what would be the correct supply to be able to run the 300 ipm I want.

Hu, I will be carving wood and I don't require the accuracy as you guys in the metal industry do. If I can maintain.0000002 that will be close enough! Seriously I am basing this speed on what I have seen much larger machines do although they were also much, much more money that what mine will be. One was a 4 head 4 axis Shoda that can carve 4 of the most complicated gunstocks made in 38 minutes and they are smooth enough you can hand sand them if you want to. I suppose you could carve them with an axe and still hand sand them if you wanted to also but that wasn't what I wanted to do. The other machine was a 10 spindle Kitako that was slower but still carved 10 stocks in about 45 minutes and they were much smoother than those on the Shoda.

I see the folks on the homebuilt forum talking about hrs and hrs to carve a small plaque or the boat model but I can't afford to spend that much time when we can carve them by duplicator faster. I need both the speed and accuracy the cnc should be able to give. I

I am currently carving one of the more simple stocks on a very slow open loop system and am having to hand index my part six times which also includes 3 bit changes. I think the stopping of the machine to change bits and hand index the part is taking more time than the carving is. The total time involved now is about 4 hrs and I am carving at 50 ipm so as you can see I am trying to get in that 30-45 min range.

All input is appreciated and more is very much welcomed. BTW if you guys that really know big and fast machines thinks this is something that will end up causing me more grief than good please speak up. I cannot afford another costly mistake.

turmite

[ger21]

Isn't a machine like that Shoda about $200,000? And you're looking for similar speed for what, $3000?

Gerry

[HuFlungDung]

Turmite, what kind of controller are you planning to use?

You are going to want software with plenty of "look ahead" to keep enough nc data fed into it for smooth motion.

You also need a motion card that can output a smooth vector profile from all the data, something like a Galil motion card is capable of. Check on Ebay, there are a few cards on there right now at a decent price compared to new. A Galil DMC 1832 3 axis PCI card might serve your purpose. Or, anywhere from a Galil DMC 1730 to 1780 ISA card might also serve, if you have a pc with an ISA slot available.

I think the motors you have selected might be adequate for 200" per minute feed, and likely 300 or 400" per minute rapid. You've got to give them time to ramp up to speed, and it is going to take a bit of distance to accomplish this. This is typically where the compromise in speed is made, because if you have a foot to accelerate in, you can get any decent motor going pretty fast. But if you want it to accelerate to full speed in an inch or less, that is where its going to be sucking hard on the power supply.

If your cuts always begin and end in the air past the end of the part, you may not have much trouble with the acceleration/deceleration factor.