Building a smaller desktop cnc machine, stepper choice questions

[imprez55]

I am building a smaller 13 x 13 x TBA cnc machine from scratch. This is meant as a budget machine that will hopefully make components for a better machine in the future (or convert a mill, but thats a ways off). The design is using the x-axis to move the y-axis, as opposed to the gantry style (so the table moves, just like a mill). The main things I will want to carry over to the next build would be my driver (flexible on this) and steppers.

Now on to the main part. I have all but ordered the hobbycnc EZ driver board and am looking for steppers. I have narrowed it down to what I think would be three different good options. The first are for all 3 axises and are here from circuit specialists. The next two options revolve around automationdirect because of circuit specialists' shady practices. I would either use two of these for the x and y axis and thisfor the Z, or just use the first one for all three axises.

Thank you for looking

[ger21]

Spend a little more and get something closer to 300 oz-in, and don't skimp on the Z motor.

Something like the KL23H276-30-6A at www.kelinginc.net

[imprez55]

A few clarification questions: Why would I need a 300 oz-in motor for such a small table? I have seen it run at much lower than even I was looking into, what would be the advantage (or reasoning) behind such a larger counterpart?

Why do you recommend the 6 wire version if the 8 is also readily available, because the driver I chose does support that? So you agree than that the hobbycnc driver would be good for this application?

Should I just get 3 of the same stepper for the 3 axises then? I just thought that since my z-axis was not heavy, a smaller motor might actually be conducive.

Please correct my flawed reasoning! I would definitely like to understand the choices here. Thank you

[TOTALLYRC]

Why not just get the hobbycnc package with the motors included?

If you use one of the other suppliers, use automation direct. I have had good luck with them at work.
Use all three of the same size motors.
http://web4.automationdirect.com/adc...P-MTR-23055The
The z is fighting gravity and you don't want the z to be too slow. Unless your z is extremly light.
Mike.

If your budget allows step up to a driver system that you will happy with on this machine and others.

[imprez55]

The hobbycnc package is $80 more than just buying the 300 oz-in steppers from either automationdirect or kelinginc and hobbycnc board for just a cap, rectifier, and 20 oz-in per stepper. Thats a little much to me considering I already have a power supply (not just a transformer). If I was just buying a transformer this would seem like a good option though. I am just trying to cut costs where I can, and this seems like a perfect place.

TOTALLYRC: you directed me to the ~200 oz-in stepper as opposed to the ~300 oz-in ones ger21 suggested. What made you decide to pick these to recommend over the 300's?

[TOTALLYRC]

Your machine has such a small footprint and they are a better match for the hobby cnc boards power output. As the motors' inductance goes up they will go slower for the same amount of voltage. The larger motor had more inductance if I remember correctly.

I have absolutely no experience with the hobby cnc products other than what the website says. I am also not bashing them.

I would make sure that it will do what you want now and in the future by reading other stuff other than their website. Do a search on the zone and the like.

Does it have optioisloation to protect the computer?
Does it have mid band compensation, without which the motors will stall at a much lower speed reducing you machines usefullness?
Have other people had good luck with it?
Will it play well with your next machine or are you going to have to buy all new components, including motors again?
If you are going to convert an X2 size mill, which is not a large machine, and very popular, will this drive it?

I know money is tight, but I learned my lesson with my taig and the xylotex driver. It is a fine product and well supported, but it isn't gecko.

Just my 2 cents.
Mike

[imprez55]

When comparing the larger motor to the smaller one at automationdirect you are correct about inductance, however the larger one ger21 posted at kelinginc is rated at 0.16 mH less than that of the automation small. I would prefer not to have to upgrade steppers on my next project so that is why I would like to get this part squared away.

I know the hobbycnc board is no gecko, but I would have quite a bit of cash telling me at this stage it doesn't matter ha ha. I have been recommended their drive so I think others have had success with it, if not it could be due to them assembling it wrong (it is a kit). I don't mind not having the best for this build, to me its more of a test of what I can do first. Next build I will definitely be more inclined to spend the cash on gecko

[TOTALLYRC]

If you want to use the steppers on the next project as well, you need to decide what the next project is and what size steppers it will need. Then see if the motors will fit both machines. The other way is to say that this whole machine is a learing experience and just use what is cheap and easy for this one. Then go "all out" for the next one.

My Bad, you are using a unipolar driver. The keling motor is 3.0 amp unipolar, which is the same for the hobbycnc board 3.0 amps max.

The automation direct motor is 4 wire and will not work with that driver.
Hobby cnc specifically says 4 wire motors won't work.
i am working on a nice Migain, so if I cease to make sense, do't mind me.

Mike.

[imprez55]

Well I think I only have one more question, the kelinginc steppers are actually rated at 200 oz-in when run in unipolar mode. The original recommendation by ger21 was to get a stepper closer to 300 oz-in. Does this mean I should be looking for a 300 oz-in stepper in unipolar, or was that taken into account already. I was thinking maybe you missed the specs on the board and didn't know it was unipolar only.

I think these will work with an upgraded driver for my next build. I don't plan to go any bigger, just more precise and possibly a 4th axis. If not, I can easily chalk it up to experience and have fun with the parts.

[TOTALLYRC]

Originally Posted by imprez55 Well I think I only have one more question, the kelinginc steppers are actually rated at 200 oz-in when run in unipolar mode. The original recommendation by ger21 was to get a stepper closer to 300 oz-in. Does this mean I should be looking for a 300 oz-in stepper in unipolar, or was that taken into account already. I was thinking maybe you missed the specs on the board and didn't know it was unipolar only. I think these will work with an upgraded driver for my next build. I don't plan to go any bigger, just more precise and possibly a 4th axis. If not, I can easily chalk it up to experience and have fun with the parts.

The motors are 3.0 amps which is max for the driver you are looking at.
Amps translate into torque and Volts into torque at speed as a general rule.
If you use a 6 amp motor, at 3 amps,you will not get its rated torque anyway.
I think they are 8 wire and can be wired as unipolar for this project, and bipolar for the next machine, with new electronics. This means they will work now and later.
In my opinion they will work fine for a small machine like you are building as you are already making choices to keep the costs down. Unless you are going to be cutting steel, which I doubt on a scratch built machine, you should be fine.
If you make the choice now that this will be a learing experience, and plan for the possibility of new everything on the new machine, I think you will be much happier.

What I try to do when building a machine is to take more of a total systems approach.
What will I be cutting? how fast is the necessary cutting speed?
How much low speed torque will I need?
Can I get all of the above for the amount of money I want to spend?
There are more questions but I forget at the moment.
Mike.

[imprez55]

I did originally try to do the "total system approach" you say, but my knowledge in this field is so limited I think a good starter machine would be there perfect learning experience. I am a hands on learner so its hard to gather the information from here and translate it without any real experience.

So yes, I will get the 8 wire ~300 oz-in steppers and wire them temporarily in unipolar with the hobbycnc board. I will only be doing an occasional PCB, but mostly wood. I hope to keep the motors and run them with a gecko for my next build.

Thanks a lot TOTALLYRC for all the help you have provided over such a short time, its much appreciated. By the way, what type of rc's are you interested in? I have an original traxxas revo for bashing and a honeybee fp that I toy around with from time to time.

[TOTALLYRC]

My familly and I ran a hobby shop for ten years or so. I have been flying planes since 1988 and r/c cars since 2004. Touring cars are my passion. Boats on occasion and I have tried helicopters on and off. Late winter, early spring, I hope to get back into it. I have taken a 1 hiatus to get the workshop up to speed.
I am always glad to help.

Mike