Newbie- Electronics sharing question

[rb765]

I am in the process of my first build to get into this great venture, but have a question that I would put to you all. The machine I am building will be an approx 20"x40" machine to start and will be using 425oz NEMA 23 steppers with a 36v power supply so that I will be able to move the electronics up to a 4x8 machine in the future.

My question is if I build a small machine also using a dremel for light cutting and engraving out of printer steppers, would I be able to use the drivers and other electronics on this machine also. I was planning to pre-wire both machines with connectors that will allow me to detach the electronics from the machine anyways for portability and to keep the electronics out of the dust of my shop when not in use. I got the idea of the connectors from some of the less expensive Chinese systems that I see on Ebay (I do not plan on buying these as I believe in getting what you pay for).

Forgive my ignorance on how the interface works as I have been concentrating on the physical build and learning the software I will be using. Times are tough right now and would prefer not to buy two sets of everything just yet. I know that I can make another mount for a dremel on my main machine, but wanted the convenience of a small unit that I can bring into the house during the winter.

Thanks in advance for any help with this.

[RomanLini]

That sounds perfectly fine.

Just make the connecters easy to get at and clearly labeled so it's as easy as possibly to swap the control box from one machine to the next.

[rb765]

Thanks for the quick reply. I hope to make the electronics side have a fixed connector with the machines having leads with plugs that connect. I have not done any research into it yet because I was not sure if this could be done, but would like to make the connection with one plug. I should be able to find something in the 36-40 pin range that will handle the current and allow for expansion to a 4th axis and the limit switches.

[doorknob]

You may find that the drive requirements are different enough between the larger machine and the smaller machine that you will need to swap more than just the motor connections in order to move from one machine to another, though...

[rb765]

Could you elaborate more on the differences? I know there might be an issue with bipolar vs unipolar wiring, but what else should I look for?

[doorknob]

For example, if the current required to drive the motors on one machine is significantly different from the current required to drive the motors on the other machine, you will probably have to adjust the drivers when you swap machines. On at least some common drivers, selecting the current may require either selecting a different resistor value (possibly even by soldering in a new one!) or setting a DIP switch or something similar.

One other thought - when you want to switch the drivers from one machine to the other, it's a good idea to first turn off (at least) the power supply for the motors (by switching the AC line switch to 'off' and waiting thirty seconds or so for any residual DC voltage to drain off). Otherwise, if you simply break the DC connection to the motors by disconnecting your multi-pin connector (or 'make' the connection by inserting the connector with a powered-on circuit), you could possibly fry some of the driver electronics (because an abrupt change of current to the motors could cause an inductive voltage spike that might exceed the voltage rating of your driver transistors, possibly including arcing at the connector pins, and you could compound the problem if you happen to rapidly make and break the connection several times while wrestling the multi-pin connector on or off of its socket).

[vger]

RB765,

I do almost exactly what you are planning. I have a small machine, 5" X 7" X 2" with a dremel spindle, and a larger 24" X 24" X 9" machine. The current to the motors on the small machine is 1 amp, and 2.5 amps on the larger machine. My drivers have a small rotary switch to change current settings so I adjust those each time I make the change. I went with seperate connectors (Molex) for the individual motors and used connectors with a different number of contacts for each. My X motors use 4 pin, Y use 6 pin, and Z use 8 pin. Makes it easy to keep them straight. All my limits and E-stop are on DB25's. I do absolutely kill the power to the drivers before making any connector change.

Steve