[cbcnc]

I have 80 oz. motors on my router that will run the machine but can be stalled and prone to lose a few steps. They are 6v 1.2a Vextas and I am running them on 24 volts. I'm using a John K. Piker 4x Unipolar board to drive them.
If I was to run them in Bipolar mode using a Xylotex board or Gheko drives would I get more torque? Would I still keep the same speed?
Would I be better off increasing the voltage to 36v and run them Unipolar?
Or should I buy motors with a higher torque?

Chris

[limbo]

Torque is made by Amps, and Speed needs Volts. Do you loose steps at very low RPM or at medium RPM? If at low RPM, only increasing the current will help.

With a piker torque drops rather quickly at higher RPM's so if you are loosing steps during rapids or fast cuts, increasing the voltage would help a little bit. Changing to Xylotex or Gecko helps a lot.

John

[radio-op]

I would agree with limbo, your best bet would be going to bipolar drives. Increasing the voltage will not help with low speed torque. I would go with the Xylotex due to the cost and the demand of your motors, the Geckos would be overkill. Now if you intend to replace the motors in the long term, it might be worth the added expence of the Gecko drives.
Bill

[Sanghera]

Hi,
I have heard that before, that gecko's would be overkill for some motors. Why would this be true, the gecko's can handle the low amps for motors, and voltage, so if you set it right, shouldn't it be fine?
Thanks.

[ger21]

The geckos will work great for any size motors up to 7a and 80V. they would only be overkill in the cost department. The Xylotex should deliver similar performance up to 2.5a and 24V, but the Geckos have the edge over the Xylotex because of the Xylotex's low voltage limit. They'll both give you the same low speed torque, but with a higher voltage power supply, the geckos will let you run at higher speeds. But, for motors under 150-200 oz-in, the performance increase from Geckos vs. Xylotex probably isn't worth the price. Save the Geckos (and the money) for bigger motors.

If you do get a Xylotex, you'll still be limited in top speed by the 6V rating. So if you want to go faster, you really should upgrade both your motors and drivers.... I just looked at your machine thread. If you're going to keep that machine for a while and want better performance for low cost, get a Xylotex and try to find some 180-200oz-in motors.

[cbcnc]

Let me see if I can put the concensus together.

Bipolar and Xylotex will get me the most results right now.

Maybe increase my power supply to 30v (Max for Xylotex)

Stronger motors in the longer run.

Save the Ghekos for a more sophisticated machine and larger motors.

That works for me, as a large cash outlay isn't justified for this machine.

Thanks,
Chris

[ger21]

Bipolar and Xylotex will get me the most results right now.

I wouldn't get my hopes up too much if you use the same motors. When are you losing steps? All the time? Higher speeds? How fast are you able to go (ipm)?

I've seen people with homemade routers, using Xylotex, 1/2-10 acme, and these:
http://cgi.ebay.com/ws/eBayISAPI.dll...808786316&rd=1

get about 30-40 ipm. ymmv

[cbcnc]

I can do 30 ipm. That is the max I have TCNC set at. When I am cutting I slow it down to 15 or 20. I seem to lose a few steps at that speed but there may be other issues involved. Namely RFI. The problem is that it is easy to stall the axes. That tells me that the steppers are underpowered (my interpretation).

Chris

[radio-op]

If you aren't losing steps on rapids at 30 ipm, then as you discribe it seems the low end torque is lacking. I would switch to a bipolar setup; not sure but you should gain 10-30 oz/in holding over unipolar. Then even if you still have a problem, going to a 120oz/in motor won't add too much more to the bill.
Bill

[cbcnc]

I think what I am going to do first is purchase a Xylotex board and build a 30v ~8a power supply. Also finish my shielded wiring.
Maybe with those things I will see an improvement. One of the things I have found out is that the Porter Cable Trim router is noisy in RFI. That may be contributing to my lost steps. I think it is in part because of the two wire power cord with no ground. Maybe I will try a 3 wire cord and ground the frame. Right now the case is grounded but through the machine framework.

Thanks for all of your advice,
Chris

[ger21]

Just a word of warning, the Xylotex is sometimes notoriously susceptible to noise problems.

[lithium]

A 6v motor at 24v!!
can they handle that?

I have some 6v motors and run them at 11.5v and they get very hot so I'm afraid they will burn out.
Are they designed to handle that much overvoltage?

Mine are 6v, 56oz-in. Japan Servo Company motors
KP56LM2-097

thanks

[tachus42]

lithium
Either your not using a series resistor or it's the wrong value. Stepper motors should really be rated by current and not voltage. The power dissipation is related to the current in the coils. Double the current and the torque doubles but the power dissipation goes up 4 times so there is limit to how much more static torque you can get out of a given stepper but you can always go faster !
The voltage rating is the max voltage you can have across a coil with the stepper stopped. When it is in motion the inductance of the coil prevents the current from building up fast enough reducing the torque as the stepper speeds up. So a higher voltage is used to overcome the inductance with current limiting circuitry or a resistor to stop the motor from burning out.

Since you have almost doubled the voltage on your steppers you need a resistor about the same value as the coil resistance. Your motors seem to be 1.2A per phase. V/I=R so 6/1.2 = 5 Ohms.

Use a 4.7 ohm resistor (the closest value you can actually buy) in series with each coil common.

[lithium]

Thanks for the reply

I'm a bit surprised at how messy the stepper scene is.
Standard DC motors have a voltage rating and that's it. Some in here are talking about giving the motor 6-10 times rated voltage!! woot? : )

When I say very hot I mean around 45degrees C. Slightly hotter than holdable.

How hot is normal if such a thing applies?

[ESjaavik]

Davs Lithium,

A general rule is up to 25 times the rated voltage. But that is using a chopper drive. It is current limited to the nameplate current and then pulses the voltage to get that current. If using resistor current limiting, then it's the voltage before the resistors. And you cannot run that too high or you would burn off a *lot* of heat in them.

The stepper itself can be hot enough to give you severe burns before it's too hot. Yours are well within working temperature. If you spit on it and it fizzes off immediately, it's too hot (>100 C)

[Zagroseckt]

Ok this may sound silly to some of yall but i've kind of wonderd why some one hasnt thought of gearing down?

[ger21]

Because noone ever wants to go slower.

[DW61]

What I am trying is a gearing up. I got a 10 tooth timing gear on the stepping motor, and a 40 tooth timing gear on the ball screw.
So the motor turns at 150 rpm and the ball screw turns at 600 rpm. So far the set works better the direct drive.

DW61


"when in trouble, you call DW"

[DW61]

oops
I got that backwards, 40 tooth timing gear on the stepper motor. 10 tooth timing gear on the ball screw.
works better than the direct drive did on my machine.

DW61

"When in trouble, call DW"

[radio-op]

DW61, how has the torque been effected, wouldn't you see a 4:1 reduction in torque?
Bill