Drive for 3-phase hybrid stepper motor

[Newbie2CNC]

Hello u all!!

I've bought 3 KT60LM06-551 (http://www.japanservo.com/digital/ge.../c_ste_019.pdf) and 1 KT60LM06-552 hybrid stepping motors, from Japan Servo, on eBay. The only problem is that i don't know how exactly to control them, since they have a very low source voltage.
I know that i have to build 3 half H-bridges (saw some interesting in International rectifier website), but the problem is that i have to source KT60LM06-551 with 2.77V. How can i acheve this? Any Drivers suggestions? I'm really confused with this, because it's the first time that i have to control stepper motors of this kind.


Thank you for reading, more thanks if you reply...


Bye!

[ESjaavik]

You can, indeed should, supply a lot more than 2.77V when using a chopper drive. Actually the voltage rating of the motor is one of the least interesting parameters. Other than it should preferrably be low enough that your DCbus voltage can be 10-20 times higher. That is necessary to get some torque at higher speed. In your case, no problem. If you look at the top of the column of torque charts, you will see that your DCbus voltage should be 24V to get these advertized torque vs. speed characteristics. With a lower DCbus voltage you will start with the same torque at 0 RPM, but it will drop more with increasing speeds.

Your problem is that most, if not all hobby-grade stepper drivers are for 2ph motors. You are quite right in your statement that your driver needs one more transistor pair than the H-bridge. It will be a I-I-I bridge instead of a I-I bridge (Drawing H as I-I). But you can use the same driver chips, as they usually come as only one pair.

[Newbie2CNC]

Thanks for the reply... In the past few days, after i posted, i've collect valuable information regarding the control of this kind of stepper motors (si-7600 from Allegro microsystems is a good example case). Besides that, some good people reminded me some concepts that were with a little bit of rust .
The only thing that makes me confused right now is the current in the widdings (U,V,W), for example, having this full step timming sequence:

U V W
1 + - -
2 + + -
4 - + -
5 - + +
6 - - +
7 + - +

This means that in the case sequence 1 the current in widding U is 7,6A and widdings V and W have 3,8 passing through? Since the datasheet says that there must be 3,8A/2-phase. The other cases are equal...
This may appeard has lack of experience... Well, in fact the problem is that i don't have any person qualified to talk about control of stepper motors and so the language in the datasheets must be well comprehended in order to do everything right and without burning something up. So... I asking YOU guys to help me to enter in this (very) addictive world of CNC's.

[Newbie2CNC]

In addition to my last post... Does anyone can explain me what are the acceptable limits for the current in a widding when it's being choppped... I read somewhere 10%, can anyone confirm this?
I was thinking of making a window comparator for the chopper drive. are there any constrains?

Thank you...

[ESjaavik]

It's 100%.

The easiest would be a chip like LMD 18245. It has almost everything you need except the sequencer. Has everything needed to hook up to a microcontroller. It also has a 4bit DAC, so microstepping is easy to implement.

[Mariss Freimanis]

Dumb question but why bother with this type of motor? The motor data shows 50 in-oz of torque at 625 RPM which is an output power of 23 Watts.

A good 2-phase NEMA23 single-stack motor can develop nearly 90 Watts of mechanical power, 120 in-oz torque and easily exceed 3,000 RPM (40 in-oz @ 3000 RPM). It can also accelerate to 1500 RPM in 0.015 seconds (mach2, unloaded).

What is the advantage here to compensate for the additional complexity?

Mariss

[Newbie2CNC]

If it's dumb and complex... give-me simple solutions!
I don't need speed... I need precision! And i'm not pushing or pulling big weights either.
Please answer to my doubts!...
These are the motors that i have and the ones that i'll work with.

[Mariss Freimanis]

Some problems do not have simple solutions. This is one of them.

Try a 3-phase switching type BLDC controller IC with a built-in pulse by pulse current limit. Set the current limit to 3.8A

Feed the 3 output 6-state phase sequence to a 3-bit D-flop. Take the 3 Q outputs back to the Hall sensor inputs. Clock the D-flop with your step pulse to increment the motor CW or CCW based on the direction input on the BLDC controller IC.

Bon appetit

[Newbie2CNC]

Well i was trying to do a microstep drive, but i think i will do firstly a simple drive using si-7600 from allegro microsystems. For the moment is the most practical chip to this situation...

[pikocnc]

Originally Posted by Mariss Freimanis Dumb question but why bother with this type of motor? The motor data shows 50 in-oz of torque at 625 RPM which is an output power of 23 Watts. A good 2-phase NEMA23 single-stack motor can develop nearly 90 Watts of mechanical power, 120 in-oz torque and easily exceed 3,000 RPM (40 in-oz @ 3000 RPM). It can also accelerate to 1500 RPM in 0.015 seconds (mach2, unloaded). What is the advantage here to compensate for the additional complexity? Mariss

If we compare the generaly 2 and 3 phase motors

3 phase motors/drivers;

1. Less vibration
2. Less torque ripple
3. Simple and cheap driver ( 6 mos and 3 mos driver )
4. 1.2 degree mechanical angle
5. low risk for resonance
6. High power