"Weak" z-axis won't plunge cutter - router turned off
 

I have a unique setup in that I have 3 motors which are rated @ 640 OZ and one 430 OZ which I use for the z axis with a 1:3 reduction.

I have a powersupply of 32V DC @ 5A to the Gecko for this axis only.

http://www.mechmate.com/forums/showt...8&postcount=22

the above link gives my motor and PS specs

When I do a plunge in Vishnu's router it pierces the MDF base - In my case it just bounces and its sort of starts jumping at the end, no idea why it does that and why there is so less torques on the motor :(

I will chk the following

1. Replace the cap on the powersupply
2. chk for wiring defects

anything else is required for checking?

RGDS
IRfan

This is the reason I prefer to have all 4 motors identical - fault finding and power supplies are easier. Unfortunately you can swop a motor to test under load, but it might be interesting to swop Geckos?

Your spring holding the motor to the rack is maybe not strong enough....what you describe ..bounces and its sort of starts jumping at the end ....I have seen if I plunge to quickly too deeply when doing PECK DRILLING.

Well tried all that - swap the Gecko - connect the higher PS to the Z motor - changed the cap on the PS - removed the spring - shortened the spring on the z motor and made it much more tighter, still problem persists .

what we are seeing is that the pinion is not leaving the rack - the motor is just oscillating at this position.

Now I need to chk now if the motor shaft is slipping..... - that's the only other decent explanation - I can have

I am uploading the video of the phenomenon - http://www.youtube.com/watch?v=tRXTGBX2F-A

RGDS
IRfan

If you have verified that the voltage is correct (when measured at the Gecko stepper driver) and if you have verified that all three gears/pulleys are tight, then the next step would be to verify that the motor is getting the necessary current from the power supply via the current-limiting resistor. Check the current-limit resistor with a meter to verify that it is the correct resistance.

Also, verify that the motor is wired properly and that the Gecko stepper driver terminal screws are firmly contacting the wire (not the insulation).

On my test bench, when I've had similar problems, the cause was either 1). low voltage, 2). wrong current-limit resistor, or 3). improperly wired motor.

the resistor same on all four drives 100K, voltage at Gecko is 32 V, wiring at all ends have wire lugs - I will again put new lugs and reconfirm the wiring.

Have you got specs on the motor?

1.7mH is a low inductance, maybe too low for Geckodrives. I have understood that Geckodrives only work for a certain range of inductances, but I don't know the exact numbers that apply for them.

That is a 6 amp motor, it needs a 282K resistor on the Gecko.

The Gecko G203v can be used with motors having inductance of 0.5mH to 20mH. The G202 can be used with motors having inductance of 1.0mH to 40mH.

With the motor disconnected from the Gecko, measure the resistance of each coil. The 'A' coil's resistance should match the 'B' coil's resistance. As Gerald noted, you should have a 282K resistor (+/- about 5%). Verify the resistance with a meter with the resistor disconnected from the Gecko.

The cutter that won't plunge into the material.....is it designed for plunging?

The cutter is the same which I have used for all the plyboard cuts and the surfacing of the table - in my other machine - it just pushes it deep - thats why I was wondering - I think I should change all the resistors - will do that tomorrow and report.

RGDS
IRfan

Irfan,

You said you were going to check the pinion and pulleys on the Z axis to make sure one of them wasn't slipping. Did you do that?

Dough - chkd everything - I also changed the resistor on the gecko to a 282K one - but still same results as in the previous video - I think it is typical of a R&P systems.

i have yet to chk the resistances on the motor coil - btw while cutting there are no problems.

RGDS
Irfan

Irfan, can you put a bathroom scale under the z-axis to see the force which your axis is creating?

(If your pinion is 0.5" radius, you should be seeing over 60kg [135 pounds] on the scale)

Definitely not 60 kilos's _ I can feel it. 60 kilos on a bit will push that bit through - the MDF - here it is not!

RGDS
Irfan

Do you have a lot of friction in your belt drive, or friction elsewhere?

no friction anywhere G' I just re-assembled the whole gearbox on tuesday and refitted it - the belt is just tight and not too tight to cause the problem.

I have yet show my doubt on the motor????

RGDS
IRfan

Does the motor's detent feel good? (Is it still well magnetised?)

how do I know about that :)

should I turn the shaft with hand and feel there is a lot of resistance?

Yes, quite a bit of torque is needed to turn it by hand. If you short the 4 leadwires together, it should be much more difficult to turn.

Irfan,

I'm not sure you have a problem. You said that when you cut, you don't have a problem. On my machine, if I turn off my router motor and plunge my bit into my support board, I only get a loud noise out of the stepper. My bit won't pierce the mdf. If it seems to be cutting okay, I think you are fine. Just keep your Z Axis feed speeds low.

On the other hand, maybe I'm misunderstanding the situation.

I am also starting to wonder if Irfan's router is running during the "pierce test"?

Dough - think you are right :)

G' on any of your machines can you try this - I don't want to run behind some problem which in the actual sense does not exist.

RGDSIRfan

Irfan, did you really expect the cutter to penetrate the MDF without switching the router on? I can't believe it . . . . .

Well on my other router it does - that let me to believe it could - here too!

Check all your grub screws.

Hennie - already done that multiple number of times :

this is something we have to leave with.

Just a thought- Is the test board the same density as your original test boards?

Hi Gerald and others,

stupid question,...if you write z-axis should bring 60kg or more on a scale (3:1 geared like irfan), does that mean direct drive z-axis is normal in the range of 20kg plunging "force" or is that too weak and indicates fault in the system?
thanks and greetings ecki