Originally Posted by
cnc1000
If I run the Gecko, will it just limit out at 7 amps and therefore, I'd have 7/8 of the torque that the original Boss 5 controls gave it? If so, I can live with that.
I'm using Compumotor drivers rather than Geckos on my Boss 3 so there may be some differences in my experience, but I think it is representative.
First, low speed torque is not an issue with these machines. The 8 amps you refer to will really only be noticed at the low end.
Second, my machine runs better at 6 amps than it does at 8 amps. I believe the different current level affects the resonance characteristics of the motors. It so happens that this resonance is more of a problem at 8 amps. I discovered this with my own experimentation.
Third, the voltage will make more difference. This is because the limiting factor is torque at a higher speed. Stepper motors have a lot more torque at low speed than they do at high speed. These machines need more torque at the high end to be able to handle the rapid moves.
The inductance of the motor will limit the rate that the current can rise in the coils. At low speed, there is ample time to get to the rated current because the phase stays energized longer, before switching to the next phase. At higher speed, due to the rpm, the phase will turn off before the full current is reached. Since torque is a function of current and the number of turns in the coil, the torque drops off at higher speeds.
Increasing the voltage will "push" the current to rise faster, thus increasing torque at the higher speeds. Geckos do this well.
The bottom line is...
1. 7 amps will work fine
2. use as much voltage as the Geckos will handle
3. wire the motor in parallel
4. MAKE CHIPS!
"Perfection is achieved, not when there is nothing more to add, but when there is nothing left to take away." Antoine de Saint-Exupery (1900 - 1944)