Tracking Board Encoder and Carving/Cutting bits on A and B series Machhines

[bergerud]

Thanks, it must be a more complicated reason. If you look at my spin up videos, how does your spin up pulse length compare? I get a very short pulse.

[ibewiggin]

Yes I have the spin up problem and my rpm sensor works as well. It does not do it when you put the bits in under the initial set up, but it does do it when you put each bit in right before being used. To me it seems like a programming issue, but that does not make sense as it does not happen to every one. I have also updated my software and that did not help either. But it is weird how in the setup it works fine.

[bergerud]

I think if it was software, we would all have the problem. It could be a time constant problem. Something like a capacitor on the base of a transistor or SCR stays charged too long. A circuit diagram would be useful.

[dbfletcher]

I watched your spin up video, and it appears to be very close to mine, however, when your truck travels to the left you can see your head make an aburpt stop, my will never be stopped by the time it gets to the left side. I have just always assumed the some machines just had more drag and the spindle was able to stop in time. I had made a suggest to add under user options a while back to let us specify a time in milliseconds after spin up before moving to allow us to adjust that. For now, I just hit stop right a soon as the truck starts moving, and then when the head has stopping spinning, hit continue again.

[bergerud]

I am exploring the possibility that the spin problem is caused by the motor controller. I will take mine out and sketch the circuit diagram. So far, I have only looked at Al's pictures. I believe the main controller part is a triac, (two SCRs for AC) controlled by pulses from the computer. These triacs work as switches which turn on with a small pulse to the gate. I have read that transients can trigger these things to turn on or stay on. In our case, with an inductive load with brushes, there must be lots of transients. An extra capacitor and resistor called a snubbing circuit is usually added to quiet these transients. I do not know if such a snubbing circuit is part of our controller or not. I only see one capacitor and if the the motor fails to run without it (as Al reports) it cannot be part of a snubbing circuit. If anybody else knows more than I about these things or about this circuit or has a circuit diagram, please jump in here.

[bergerud]

I do not know if anyone in interested in this but I have taken a closer look at the controller circuit and the capacitor and series resistor are the snubber circuit. The resistor and capacitor are in parallel with the triac. The main purpose of this circuit is to smooth out voltage spikes and transients that would trigger the triac to turn on. My theory as to why the cut motors keep running is that this snubber circuit is not able to handle the electrical "noise" from motor brushes. The triac turns off cutting power to the motor but then the noise turns it back on and then off and so on. This "feed back" loop dies out but the effect is that the motor is speed controlling to a stop instead of just stopping.

I would like someone with this problem to video it as I videoed my spin down so we can compare. (Use a thick board so you can let it spin.)

If the theory is right, this problem should happen more often with old motors with rough commutators and/or motors with worn out brushes. New motors should behave. (Why does the motor jump sometimes when you close the lid? A transient that gets past the snubber?)

Lets find out first if this is the problem and then maybe someone with electronic expertise can find a solution.

[Digitalwoodshop]

Good Discussion.... I am too busy with deadlines to jump in.... I will watch when I can...

AL

[dbfletcher]

I probably wont have a chance until this weekend, but I will take a video of my machines spin up, so you can see. I'll check the current hours on it as well, but both of mine had done this since day one.

[Digitalwoodshop]

It would be interesting to do a spin up test then change the brushes and try it again...

AL

[bergerud]

Doug, if both of your machines have always done this spin up thing, it makes me wonder. How many machines do this? Do some of the C machines do it?

If my machine did it, I could experiment with it. I would test the components and try replacing the triac. Has anybody replaced the cut motor control board to solve the problem? I would like to have a bad controller to test.

If anyone at LHR knows anything about this slow spin down, please help us and chime in.