Confused about Steppers and Voltages.

[cap9qd]

First off i am building a gantry mill and have built and tested 3 linistepper drivers. I have some small Vextra 12V 0.5A motors (50 Oz-In) that i planned to use for this but i know that these just wont hack it. I am looking for new motors and was thinking of getting some of the #23-200-DS8 (200 oz-in) motors from HobbyCNC. The question is that these are rated at 3V and 3A. The driver board that HobbyCNC sells says that they recommend you run it at 24VDC or more. So im confused about the rating of the motor? I dont think that my linisteppers are going to hack it either since i dont think they handle more than 1.5A. Any insight would help me out alot. Thanks!

[ger21]

If you only supply 1.5A to a 3A motor, you'll only get half the torque. Torque is proportional to the current supplied.

Typically, you'll want to supply a stepper with 10-20x the motors rated voltage. A stepper's torque falls off quickly as rpm's increase. Higher voltages allow current to flow through the motor faster, maintaing torque at higher rpm's. Doubling the voltage will usually double your useable top speed. Too much voltage, however, will cause excessive motor heating, so there is a limit to how high you can safely go. Usually around 20-25x the rated voltage.

[cap9qd]

Thanks for your help. Makes sense since the faster you switch the coil the more the coil resists the flow of current. I’m an electrical engineering student and my intuition said run the 3V motor at 24V and you let the magic smoke out.

I’m not sure what to do. I was doing some research and it looks like I can use the Linistepper drivers at up to 3A or so with some tuning of the current resistors. What do people suggest I do? Should I dump the Linisteppers and go with the HobbyCNC CNC kit or should I give them a try? I am going to buy the 200 oz-in motors though. Thanks for your help.

[pminmo]

If you want to build something might take a look at my website:
http://PMinMO.com

just added some info on 6 wire motors:
http://pminmo.com/6wire/6wire.htm

[jeffs555]

Since you already have the linisteppers, you might give them a try. The main problem with the linistepper will be power dissipation of the output transistors, so you will need more heat sinking and cooling than you would with a chopper drive. At low speeds, the power that the output transistors in the linistepper need to dissipate is equal to the supply voltage minus the motor voltage then multiplied times the motor current. Increasing the supply voltage will greatly increase the power disipation and heat. The maximum disipation for the TIP122 output transistors depends on how cool you can keep them. At a case temperature of 80 degC it is only about 30 watts, so at 3 amps, you would be limited to a supply voltage about 10 volts higher than the motor voltage.

With a chopper drive like the HobbyCNC, the heat dissipated by the transistors in the drive depends mainly on the motor current, and increases very little as you increase the supply voltage.

[cap9qd]

Well the more i read if i dont want to used the microstepping of the linisteppers then if i have a large heatsink (okay...really big...) then i should be able to get away with it. Then if i want to upgrade to the chopper drive later i can do so and get some more accuracy out of my mill. Thanks for all your help guys...im sure ill be back befor this is all said and done!

[cap9qd]

I decided to just do it right and what is proven to work and just bought the HobbyCNC 4 axis kit. I plan on only using 3 of the axis now...but figured ill use the 4th axis eventually so why not. Thanks for your help guys!

[James Newton]

Just so you know, the Linistepper activly regulates the current supplied to the motors. So no matter what you supply it with in terms of motor voltage, it is only going to allow the specified amount of current to flow into the motor. You can change the sense resistors on the Linistepper to allow more or less current.

The Linistepper kit is rated at 1.5 amps/phase in microstepping modes and 3 amps in full or half step. More than that is possible but A) you have to be very carefull and know what you are doing and B) you may fry the drivers. If you do, they aren't terribly expensive to replace, but best to do it right. I've seen Linistepper run 5 amps in full step mode, but I don't recommend that.

Over all, the bigger the heatsink, the better. Active cooling with a fan is a good idea but should not replace the heatsink.

Since the current is regulated, the supply voltage can be much more than the rated voltage of the motor. Much higher supply voltages allows the driver to get the winding voltage up right now! and so supports faster stepping and reducing missed steps.

In normal operation, the supply voltage to the Linistepper should be 2 to 3 times the motors rated voltage but of course, what ever current is not allowed into the motor must be dissipated by the drivers on the Linistepper so high voltage equals more heat.

Microstepping controllers can supply much more current without the controller getting hot, but the motor will run hotter due to eddy curent losses in the windings.

I sell the Linistepper kits just in case you don't know.

[cap9qd]

Thanks for your help. You are alittle too late...i already bought the other driver. I am undoublitly going to build another CNC (everybody does!) so i am going to save them. I have them hooked up and running very well (the Linisteppers). I have them running my Egg Plotter right now. Thanks again!