Linistepper update

[student1616]

thanks all of you for designing and updating the linistepper.
iam following posix made epineh modified linistepper layout.i am trying to make professional board.once i get them i'll populate and test them.
mean while i have a doubt.i'll be mounting all of them(3 boards) on one big heat sink.so is it ok if their grounds(TIP122) become one.i can place a insulator in between them.still i wanted to know what will happen if their grounds get shorted.
and isn't possible to adjust the current using pot and a resistor combination? like in L297+L298 where we see reference voltage and adjust the current accordingly.
my motor is rated at 0.95,so i placed 2 1ohms resistor on board.and it felt like current is low.bcz i can stop the motor if i hold it tight.i need more torque.(i powder the board using 12v supply and use ATX supply.)

[James Newton]

If you short the transistors, they will blow up.

Yes, you can use a pot to fine tune the current, but it must be a high power POT, just like the high power resistors.

You didn't say what voltage your motors are rated at. You should use a power supply that is more than the rated motor voltage; up to 2 or maybe even 3 times. If your motors are rated below 1 amp and 6 volts, that is only 6 watts of power... you /should/ be able to stop a 6 watt movement with your hand. No driver will make a difference with that. Get a more powerfull motor (e.g. 2 amp 6 volt or 1.5 amp 12 volt with 24 volt supply) and you will have better luck.

By the way, you do know there is a very nice professionally made PCB already availble for less than anyone could possibly have one made? They are available for 3 for $35 at
http://www.piclist.com/techref/io/st...index.htm#kits and there is a kit with all parts at that same page for $35 each or 3 for $30 each. Each board is 1 axis, but there is no reason you can't hook all 3 to one heatsink.

[student1616]

thanks for the reply james.
abt placing all the transistors on one heat sink,seems a bad idea.so shld i place a separate heat sink for each transistor of a board?
all i wanted to know is,if i place a board on one heat sink,whech has 4 TIP's,their collectors will get short.so is it ok?

and iam using 3 motors.2 rated at 4V@0.95A and one 4v@1.3A
i think i'll go for higher voltage.now iam using 12v.so may be 24v will solve my problem.

and can't i just use a 1Ohms-5watt resistor and a small trip pot combination to get the required current setting?

[James Newton]

I don't know how to be more clear on this: If you short the transistors together, they will blow up. The kit I supply comes with mica isolation spacers and washers to keep the mounting bolts from contacting the heat sinks electrically.

The supply voltage should be at most 2 to 3 times the rated voltage of the motor. With those tiny little 4 volt motors, your 12 volt supply is already more than they should be getting. Again, the issue is that they are tiny motors. Nothing is going to make them stronger.

The current that flows through the 5 watt resistor will also flow through the trim pot. If it isn't rated to drop the watts, it's going to melt. Ohms law is a law.

[ejohn]

Originally Posted by tivoidethuong did you make Hex file for pic16f628A?

another question,
can I insert PIC16F84A to Pisox's PCB ??
because may be I can only programe PIC16F84 now

[student1616]

i got it.thanks.those mosfet shouldn't have single ground.i ordered some mica spacers along with plastic screws.bcz if i use metal one,i might short the collectors.
below is the pics of my motors(some guy posted it.thanks)
http://www.cnczone.com/forums/attach...0&d=1192411595
http://www.cnczone.com/forums/attach...2&d=1192411595

i ran these before with L297+L298 combo.and they did well.but it was in bi-polar config.i know bi-polar gives more torque than uni-polar.

[student1616]

I tried both A and non-A versions of PIC.both worked well.

@James Newton
sorry for bothering you again and again.
i couldn't find any motor which is abt 1.5 to 2A current rating.
but i have some whose rating is 3.6v@2.9A.i know i can't run these at 2.9,as the linistepper is not capable of it.
but what if i run the same at 2A.it will give me low torque but at least it will give me more torque than previous one.
so can i do like this?
and say if i use power transistor like 2N3055.can i pump in more current?

[student1616]

Man... its a big mess.
at last i found out the issue.
It was the resistor i used (1 ohm-5watt).but when i measured it.its showing 2.5ohms.so i bought 2-0.5ohms resistor and tested the motor and board.
it worked well.the motor was drawing 1.8A(motor is rated for 1.3A per phase) and the torque is ok.(better than previous)
and i mounted the TIP's on a really big heat sink.(i tried IRLZ44 but the didn't work.i guess pin config is same as TIP)
i'll try much lower values of sense resistor.i know min possible is 0.6ohms as per the tutorial.but what worse could happen?motor will run hot.as stepper is designed to run at 50-90 degree,it is ok for me.it is lot better than L297+L298.

My Heat sink is 4''X12''.so iam planning to mount all the TIP's at equal distances and will use pulgin type wires to make contact with the board.

[James Newton]

You can run any motor that is rated higher than the current you put into it, and probably you can get away with "overclocking" a motor a bit as well, as you suggest. It might burn out the motor, but that is the risk you take.

You can "beef up" the transistors on the Linistepper to manage more current, but heat will be the limiting factor. You can only move so much heat away...