Epsom steppers EM236

[wijnendael]

I recently removed a couple of motors from a old epsom printer EM236 & EM237. i am running the EM236 with a L298N ic and everything seems to work ok. However the motor will not run at a fast speed like it does in a printer when it travels very fast from one end to the other, is this because of the code i am using or does it have to be done through gearing ? my code is as follows:-

	let dirsB = %00001111			; make pins output
main:	for b3 = 0 to 20 			; start a for...next loop
	if pinc.0=1 then 
	gosub lstep
	endif
	if pinc.1 = 1 then 
	gosub rstep
	endif
	next b3					; next loop
	goto main				; repeat

lstep:	let b1 = b1 + 1				; add 1 to variable b1
	gosub stepit				; do the step
	return

rstep:	let b1 = b1 - 1 			; subtract 1 from variable b1
	gosub stepit				; do the step
	return

stepit:	let b1 = b1 & %00000011 		; mask lower two bits of b1
	lookup b1,(%1010,%1001,%0101,%0110),b2	; lookup code into b2
	let pinsB = b2
	return

 

[Dippy]

I can't help with the code, but are your power supplies and wiring good enough?

 

[wijnendael]

As far as i know the psu and wiring are good. As i am not sure what the operating voltage of the EM236 is i have tried on 9v and 5v. On 9v i am getting around 1A when running and on 5v around 500mA, so if anyone knows the correct voltage for these motors i would be grateful. The code i have used is pretty standard and has been taken from somewhere else on this forum i think with a couple of small mods. If i insert a pause before the next statement then i can slow the motor down but i do not know if it is possible to run the motor faster without adding some sort of gearing.

 

[hippy]

It could be the code. Don't forget even the simplest commands take around 250us at 4MHz. There's plenty of scope for optimising the code and you can use SETFREQ to increase speeds.

 

[SAborn]

Most steppers will run slow off a picaxe, and the epson steppers are 3.6 degree steps i think so will be faster than normal (1.8 degree) but will still be slow compared to a PC controlled motor.

My cnc motors travel at about 200mm per minute off a picaxe and about 800mm per minute off a pc, or even faster still if i dont mind the reduced torque.

Have a look on some of the cnc forums as there is much discussions on how slow the L298 actually is as well, and this might be where your problem is.

 

[matherp]

To get speed with a L298 (or any other driver) you must use the L297 (or similar) to drive it. For each step you have to overcome the inductance of the motor coil you are trying to energise. The way of doing this is to use a much higher voltage than the notional spec of the motor but to monitor the current flowing and keep this within spec typically by PWM. This is what the L297 does for you. I can run 1500mm/min using a L298 in half step mode with a 5mm/rev drive. I use the L298 boards from pminmo.com which are OK but fiddly to make. I keep meaning to do a new layout of this design to also allow L298 in parallel which can give a 3.5A drive

Best Regards

Peter

 

[inglewoodpete]

Some stepper motors need an "acceleration" stage to get up to full speed. If you hit them with a pulse sequence at their fastest rated speed, they can sit and hum due to mechanical inertia.