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

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

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

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.

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.

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

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?ViewItem&category=12577&item=3808786316&rd=1

get about 30-40 ipm. ymmv

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

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

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

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

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

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.

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?

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)

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

Because noone ever wants to go slower. :D

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"

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"

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

right now I only have the "X" axis this way. I am changing the "Y" and "Z" also.
Before I change to the timing belts, My machine would not go over 10 ipm with out losing steps.
Now with the stepper only going 150 rpm, I think I have more useable torque, (lower rpm, higher torque)
Due to shaft whip I can only go 30 ipm with no lost of steps.


DW61


"When in trouble, you call DW"

Okay, I was a little confused. You have a 4:1 increase in torque and a 4:1 reduction in RPM? Sounds interesting.
Bill

Bill, he didn't day he had a 4:1 increase in torque, just more useable torque. Because steppers at low voltages usually have torque curves that drop very fast, by keeping the rpm's down to 150, he's probably able to get almost constant torque all the way up to his machines limits, vs. before where he didn't have enough torque at higher speeds. But for any given motor speed, the 4:1 reduction in rpm should give him 1/4 the torque, I think. But that 1/4 is more than he was getting before, probably.

So, let me recap, 40 tooth on the stepper and a 10 tooth on the ball screw, 4:1 gear up to the ballscrew. DW61 can run the steppers at a lower speed to achive the same rapid, what his table can take, 30ipm. By doing so, the motors are at a better part of the torque curve. Yes that makes sense, but wouldn't the holding torque still suffer a 4:1 reduction? Couldn't there be lost steps during a hard cut when the feedrate is low and you need high torque? DW61, I'm sorry if I seem to be nit-picking (if it works don't fix it), just trying to get some insight. With small PM DC motors they have 1-2000 RPM but not a lot of torque and you need about 10:1 reduction to move a load. Of course they develop their torque at high speeds unlike a stepper.
Thanks for the input.
Bill

It will take me another day to get my machine put back together so that I can test it. I will post then.
I think I have more useable torque with 40 tooth timing gear on the stepper motor and 10 tooth timing gear on the lead screw.

DW61

DW61, please keep us posted, I am interested in how your changes work out. I have seen quite a few servo systems using timing belt transmissions and assumed that was to improve the torque/RPM balance.
Thanks
Bill

I got my machine back together last night. I ran a program at 30 ipm with no lost steps, Before I could not run at 12 ipm without losing steps with the same program.
Seeing my machine cut at 30 ipm was GREAT!!!!!

BTW: 116 oz motors, 24 VDC, Xylotex boards, 22"x22"x4" cutting area,


"When in trouble, You call DW" (Theme form Dark-Wing Duck)

This is the same theory I used when designing my router. The motors I have are 2.3a bipolar series. Since the Xylotex can't run them in parallel, I have to use them wired in series, with the resultant lack of high speed torque. So, I decide to use 4 tpi acme screw (1/2-8 2 start), to give me higher rapid and feed speeds while keeping the motor at lower speeds where the higher torque is. If you're getting good results with those 116oz motors, my 252oz-in motors should work out good for me. Btw, what type of leadscrews are you using?

I have 1/4-20 all thread. That come to .000125 per step. I was going to start cheap, and later if I need to upgrade to something else.

DW61

Let me just think out loud:

So if I replace my 1/4-20 lead screw with a 4 tpi acme screw I should be able to go 5 times faster as I am going now with the motors turning the same speed. With less shaft whip. due to the bigger dia. screw.

DW61

Ah Ha! But you also get a decrease in resolution - or how small a distance you can move? (at least theoretically)
These seem to be the trade-offs. Just wondering if you know what the machine will do now (measure it) and if you change - what it does then.
It would be good data from your experiment for all!
Cheers - Jim

So if I replace my 1/4-20 lead screw with a 4 tpi acme screw I should be able to go 5 times faster as I am going now with the motors turning the same speed. With less shaft whip. due to the bigger dia. screw.

Yes, but you will also have about 1/5 the torque at the nut (I think that's right) , plus, you'll need more torque to turn the larger screw.

You'll probably need a bigger motor to compensate for the loss of torque.

Ah Ha! But you also get a decrease in resolution - or how small a distance you can move? (at least theoretically)

With a 200 step motor, and 4 tpi, the machine "theoretically" can move in .00125" increments. Is anyone's homemade router that accurate?

Righto! I won't quibble over the capability of homemade DIY machines, but DW61 said earlier:

I have 1/4-20 all thread. That come to .000125 per step. I was going to start cheap, and later if I need to upgrade to something else.
and now (from ger21):
With a 200 step motor, and 4 tpi, the machine "theoretically" can move in .00125" increments. Is anyone's homemade router that accurate?
That does represent a 10x decrease in capability.

I just wanted to point out how integrated the choices we make on these systems. In this effort DW61 is trading off "speed for system resolution" and "speed for torque" (previous posts). And of course, forr all these choices there is a "bill to pay."
This may be a less expensive path than trading motors for speed and torque while maintaining the same resolution. Given he's replacing Allthread -- the costs are small. But if ballscrews were involved - he might check the cost of a new motor for the one axis.
Cheers - Jim

I check on replacing my stepper motors with bigger ones,($200+ for each motor- times 3 motors-). That is when I found the timing gears and timing pulleys. Parts order off the net for 3 assembles $75. I did the "machining" on the plates on a drill press and a scroll saw.

So now I can cut at 30 ipm, I think I will keep my allthread for now. Next I am going to look at ways to keep the shaft whip down.

I will be happy with +/- .005 on the parts I will be cutting.


DW61

Can you apply tension to the rod, and support both ends with bearings?

I have bearing block at both ends, made out of MDF on my machine (it takes a milling machine to make a milling machine). I have roller skate bearing in the blocks with nuts holding them in place. The all-thread is ~36" between the bearings. I think this is why I am getting so much whip when the all-thread spins at 600 rpm.

DW61

Try pulling them tight between the bearings, and lock them in place to hold the tension. It might help a little, but you're probably just asking to much from the 1/4-20.

I'm glad to hear of the positive improvement on your table DW61, as well as the discussion you sparked. I for one have 'designed' by the rule of "if it worked for him, should work for me." My first 'instinct' would have been to save for bigger motors, which in your case is the most costly route. The design trade-offs concerning steppers continues to surprise me.
Bill