Jeshua Lacock wrote: > > Well lets just say the only thing that I am sure about is the drive is > under-damped. > > ;) > > Tuning is proving to be insanely difficult for me, I guess mostly because I > don't really have much of a clue what I am doing. It is also kind of scary > because if I turn a POT on the Gecko just a tad in the wrong way the drive > violently rattles the whole table. > > When it was just the Gecko, that was something I had a grip on. But now it is > a combination of the Gecko and the PID settings. > > So, first you need to tune the Gecko, by itself, so that it works OK. Set DIP switches 1-4 to OFF, to go to open-loop mode. This allows you to generate step pulses without LinuxCNC trying to respond to the movement. Get the drives set stably, and you may just want to turn down the "gain" setting until it is stable. Gain is not so critical, as you will be increasing it when you go to closed-loop mode. Once the Gecko is working OK in the open-loop mode, set the switches to ON, and observe performance. Start with low settings of P, and minimal I and D. Increase P in small steps until the following error gets better, and then add a bit of I and D to get the best performance. That procedure is described in the document I sent the link to. > It may be that I am just trying to accelerate the drive faster than the > system can adequately damp it. This gantry is probably close to 200 pounds, > and I just don't know how fast I can expect to be able to accelerate it. > Yes, possibly. You might put an amp meter in the motor wires and see how much it draws, but you can actually detect this with Halscope. By slowly increasing the acceleration until following error spikes, you will know the acceleration the system is capable of. > Does gearing a drive help with this? I seems in my mind it should. Gearing it > down further would give me increased torque and resolution so seems like a > win win. > Yes. Gearing down increases torque at the leadscrew. The only downside is that the motor rotational inertia is increased by the gearing down. To reach the same linear speed, the motor needs to accelerate X times faster, where X is the reduction ratio. But, when you simply run out of torque, then the reduction helps. But, there's no way to know for sure whether this is really your problem.
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