HobbyCNC board Z-axis losing steps

[raiven]

Hi everybody,

I hope you guys can help me with this one. I build the hobbycnc board and hooked up my 3 80oz-in steppers. I ran a test with TurboCNC and noticed that when I jog the z-axis slowly the motor just "wobbles" (takes 2 steps CW, 1 CCW). On high speed jog it turns OK but has no torque (I can stall it by just laying a finger on the axis). The X and Y-axis both function normally. I tried swapping motors (X to Z, Z to X) but this has no effect. I'm at a loss.

Any suggestions?

Thnx,

RaiVeN

[ger21]

Is the z-axis binding. Does it turn easily by hand?

[H500]

Do you have your coil phases hooked up correctly?

[raiven]

The motors are not on the machine yet (still building. So little time ).
I checked the connections to the board. All motors are hooked up exactly the same. Is there anyway to check if the driverchip is dead/dying?
I have got an scope available but don't know what exactly to look for. I also read somewhere that chopper drivers are sensitive to noise due to the high frequencies. Any thoughts on this?

Thnx,

RaiVeN

[H500]

Noise could be the problem. Ideally, each board should have there own power and ground wires going direct to the filter caps. It might also help to use a shielded signal cable and also try different grounding points for the signal. Sometimes it's more an art than a science.

[Chris D]

Check for binding, chances are real good that is the problem providing you have everything corrrect on the board. Check again the obvious, current setting and missing or bad (Cold) solder joints.

80 Oz in is not much force at all. I have 200 Oz in on my router and I can grab the ball screw with my hand and stop it from rotating, or, if stopped, I can overcome the holding torque of the motor. If anything is not aligned good binding will occur and even the slightest binding can cause a motor to have fits. Also, keep in mind that the Z axis (if vertical) has to overcome the weight of the entire moving assembly. Gravity is working against you.

Chris

[raiven]

Thanks for the suggestions guys. I'm going to test some things when I get home from work. I'll keep you posted on the progress.

RaiVeN

[joecnc2006]

Originally Posted by Chris D Check for binding, chances are real good that is the problem providing you have everything corrrect on the board. Check again the obvious, current setting and missing or bad (Cold) solder joints. 80 Oz in is not much force at all. I have 200 Oz in on my router and I can grab the ball screw with my hand and stop it from rotating, or, if stopped, I can overcome the holding torque of the motor. If anything is not aligned good binding will occur and even the slightest binding can cause a motor to have fits. Also, keep in mind that the Z axis (if vertical) has to overcome the weight of the entire moving assembly. Gravity is working against you. Chris

Interesting you mentioned gravity, I took this into consideration on my large machine i built, and used Springs to help the motor lift tool. It was a Fast and Easy solution.

http://www.cnczone.com/forums/attach...achmentid=7257

Joe

[miljnor]

I just built a 3 axis set up on these boards I had a similar problem and it ended up being a bad solder joint on on of that axis components (don't remember which piece).

did you set the trim pots as per the instructions?

If I would have done this I would have seen my problem right away. because the voltage reading i was getting was spotty and not what it was supposed to be.

thats my two cents.