Where's the beef???

[B0SC0]

Hi all,
Just about finished with my Rockcliff 18"x18"x7" router.
I am using an ebay 3 axis TA8435H driver board from Univelop Tech LLC.
It is mounted in a small server case with two switch mode power supplies. One is +24v @ 8 amps and the other a multi-voltage which I am using the +5v for the driver pcb and +12v for a fan on the heatsink of three TA8434H's.
I am driving three 8 wire uni-ploar stepper motors with each axis wired in series. These are the kelinginc KL23H286-20-8B
dual shaft 425oz in motors.
With them wired in series mode, current should be 8.4volts@1.4 amps.
The driver pcb will do 1amp or 1.6amp and steps full,half 1/8etc.
I have it set for half turn @ 1.6amps.
My leads screws are 1/4" x 20T
I am running MACH3.
Motor tuning is set for 200, 125,9, 5us for all 3 axis. This has been the smoothest running that I have been able to attain.
Running(jogging) the y axis, maximum speed is 10s an inch.
That seems really SLOW to me(hence the "where's the beef?), The other two axis about the same.
If I try to make adjustments in motor tuning, I usually get the motors "rumbling" and not turning.
Now according to what I have read, with my setup, I should have motor tuning set to 4000 for half turn@1/4"-20T screw.
I tried this and at 2000, the motor just rumbles and screw doesn't move.
Can anybody tell me what I am doing wrong????

TIA

B0SC0

[ger21]

Originally Posted by B0SC0 Can anybody tell me what I am doing wrong???? TIA B0SC0

Unfortunately, lots of things.

First, I guess, is the 1/4-20 leadscrews. Steppers motors have less torque, the faster they go. For best performance/resolution, ideally, you want between 2 and 4 turns per inch. You have 20, so you're top speed is decreased by 5-10 times what it *could* be.

Second, bad combination of steppers and drives. First, the motors. For maximum performance, you want to supply a voltage equal to 32 times the square root of the motors inductance. So, ideally, for maximum performance from those motors, wired bipolar series, you'd want about 165V. At 24V, you'll only get about 1/6 of the top speed you *could* get, since speed is roughly proportional to voltage. Bipolar parallel offers much better performance than bipolar series. But your drive is limiting you there, due to the current limit.

By setting your steps/unit in Mach3 to 200, instead of 4000, when you tell it to move 1", it'll move 20". So it really needs to be 4000.

Now, how do you fix it? How much do you want to spend?

In an ideal situation, the best you'll get from 1/4-20 threaded rod is maybe 30ipm. But you'll never get it with those motors. Something in the 100 oz-in range will probably be best for that combination of screws and drive. If you really want to go faster, You want a drive that can output at least 2.5-3amps. Then get some 170-250oz-in motors, and change the screws to something like 3/8-10 acme. That would get you up to maybe 75-100 ipm.

For right now, set your steps to 4000, your velocity to 30, and your accel to 2 or 3 and see if you can get it moving.

[B0SC0]

ger21, thanks for the fast and detailed response.

I have on hand some Vexta steppers.PH268-22 6 wire uni-polar 12v 0.68amps 125 oz in. that I tried, but had this same problem.
Then I bought the 425 oz in steppers thinking that would be better.

With what I have, what would work the best with the minimum about of extras I would have to buy;lead screws, driver, power supply, etc?

I'm thinking of changing the lead screws, as you mentioned.

How about the driver settings? full,half,etc. What would work the best? I have read that full has resonance problems.

Also, I know electronics and can build my own drivers, power supply,etc. if I need to, just wanted something faster at the time.

I plan on doing some wood carvings, pcb's, and various parts to make other things. Some small aluminum parts would be great,but not necessary at this time.

B0SC0

[ger21]

Generally, for motors, the higher the current and lower the voltage, the faster they'll go. 12V steppers aren't going to help much. Ideally, you want steppers in the 2-3V range.

The power supply would be fine, with different motors. I use a Xylotex, 250oz motors and 1/2-8 2 start acme screws and get 150-190ipm at 24V.

Like I said, the 1/4-20 will limit you to about 30ipm, maybe a little faster. 30ipm is 600rpm from the motor. On my machine, 600rpm is 150ipm.

However, I don't think changing screws will help you too much.

Cheapest thing to do, is probably change the screws to something with between 2 and 10 turns per inch, preferably acme, as they are more efficient. And look at a HobbyCNC drive, for under $100, soldered yourself. I've seen those motors running on a HobbyCNC aith 1/2-10 acme get close to 100ipm at 36V. At 24V you'd get less, but maybe enough for your needs.

[B0SC0]

What motors are you referring to; "I've seen those motors running on a HobbyCNC".

The power supply is a POTrans 24v@8 amp ~$20

If I purchase a second one, I can bump up the voltage to 48v wired in series @ 8 amps.

Of course, I will need to use a different driver;higher voltage and higher current.

I am hoping not to buy, yet another set of steppers.

But I also want the best bang for my buck

B0SC0

[ger21]

Originally Posted by B0SC0 What motors are you referring to; "I've seen those motors running on a HobbyCNC".

Your 425oz-in ones. Wired unipolar for the HobbyCNC, they'll be 2amps, 6V, and about 300 oz-in.

[B0SC0]

thanks ger21 for your help.

I am going to do a little more research before I make a decision.


B0SC0

[ger21]

Originally Posted by B0SC0 I am going to do a little more research before I make a decision.

That's what I usually like to recommend.