Originally Posted by pminmo  I like to use extremes sometimes to make a point. Consider one screw is 10 tpi, the other is 11 tpi, they wont travel very far without binding. Now lets get more practice, realize that all screws have tolerances, one maybe 10.001 tpi, the other might be 9.998 tpi, then factor in that they aren't necessarily linear, one maybe 10.002 for the first foot, then 9.998 the next foot, and the other is opposite in non linearity. What you wind up with is along the length of the travel, mechanical inefficiency. As long as you have plenty of power, it's not a big deal. BUT steppers loose power significantly as you go up in rpm's. This mechanical inefficiency becomes an issue. |
Now, if your gantry has some flex and could easily rack maybe .1 or so, wouldn't that cancel (wrong word) out the inefficiency? As the two sides aren't really fighting each other, just moving a little differently.
I'm curious, how much of a performance hit are we talking here? 5%? 10%?
Now, connect the two motors together with a belt, and they'll be fighting each other constantly, which would be a much greater performance hit.
Well, I can tell:
1. You power off machine;
2. Your kid (or any other person) enters the room and spin one of the leadscrews.
3. You guess what's next. |
You home the machine to square it back up.
On my router right now, I have my Y axis (single motor) set at 185ipm rapids. The dual motor X axis is set at 175ipm. The reason for that is I have a slightly bent screw that starts whipping and binding in a certain area. I'm fairly confident that when I straighen the screw a ittle later this week, I can get the speed about the same as the Y axis. And it's moving about 40-50 lbs more weight. So I don't think the performance hit of two motors is very great.
And, it's a lot easier to use two motors, then build a gantry that won't rack.
