Originally Posted by sixpence *snip*
4.motors: 12v .48A 1.8 deg
from rs components no:191 8340
5. drivers:built from scratch using L298 and L297 chips
from Geoff Williams book "build your own workshop bot(I don't want to do that again , ever) . Using 2 computer power supplies. 5v for the boards and 12v for the motors
*snip* |
I'm quite sure the motor/power supply combo is your problem. What's your maximum step rate before the motors stalls?
If you power the windings with the motor's rated voltage, the rated current will flow through the winding, which will give full torque, which is great. This is when the motor is stalled.
But the motor windings have an electric property called inductance, which resists the flow of current; that is, it takes a short moment for the current to build up after you (or rather the driver board) apply the voltage. So as soon as you start to switch the windings (as when the motor starts to turn), because of inductance less current will flow. The faster the motor spins, the less current, which means less torque, and the motor misses steps or even stalls.
If you increase the voltage, the current will rise quicker, and so the motor will give more torque. But now the problem is that when the motor is stalled, too much current flows and the motor overheats.
The solution is to regulate current. Two ways are common: using series connected power resistors or transistors (very inefficient and the resistors are expensive and get very hot), or using a chopper drive.
The chopper drive is fed with many times the motor's rated voltage. It monitors current and when it is lower than optimum, it applies more voltage to make it rise faster. When the current is at the rated value for the motor, it regulates the voltage so that the current doesn't rise any more.
So you probably need different motors, different power supply, and/or different motor drivers.
Arvid