[pmurdock]

G'day all,

I've got an Applied Motion stepper (HT23-401) NEMA 23 , 187 oz/in holding torque motor, 3 V, 3 A/Phase hooked up to a Gecko G202 drive. Power supply is 36V 4.5Amp supply. Motor wired up in Bipolar Parallel (8 wire motor)

Arduino connected to this on the Step, Direction, and Common (+5V) ports on the Gecko..


I can get it up and running - but even with the Arduino doing nothing and supposedly full holding torque I can move the shaft on the motor.. It's tight don't get me wrong, but I can defintely move it (should I be able to do that with 187 oz/in holding torque?

I have the current set resistor to 68kOhm to provide roughly 4 amps.


HOWEVER even though the current set resistor is set for that I only see about 0.7 amps off the power supply in holding position.. I am wondering if the Gecko drive is shot somehow.. I did the test as mentioned here on the forum and none of the MOSFET's showed 0 Ohms to either GND or VCC.


When I spin to higher RPM there is absolutely no strength (torque) I can stop the spinning with my hand freely.


any ideas?

cheers,
Paul

[storm2313]

G'day all,

I've got an Applied Motion stepper (HT23-401) NEMA 23 , 187 oz/in holding torque motor, 3 V, 3 A/Phase hooked up to a Gecko G202 drive. Power supply is 36V 4.5Amp supply. Motor wired up in Bipolar Parallel (8 wire motor)

Arduino connected to this on the Step, Direction, and Common (+5V) ports on the Gecko..


I can get it up and running - but even with the Arduino doing nothing and supposedly full holding torque I can move the shaft on the motor.. It's tight don't get me wrong, but I can defintely move it (should I be able to do that with 187 oz/in holding torque?

I have the current set resistor to 68kOhm to provide roughly 4 amps.


HOWEVER even though the current set resistor is set for that I only see about 0.7 amps off the power supply in holding position.. I am wondering if the Gecko drive is shot somehow.. I did the test as mentioned here on the forum and none of the MOSFET's showed 0 Ohms to either GND or VCC.


When I spin to higher RPM there is absolutely no strength (torque) I can stop the spinning with my hand freely.


any ideas?

cheers,
Paul

Paul,

Please read my post on understanding steppr motors. It will explain to you why the power supply is reflecting only .7a of current. http://www.cnczone.com/forums/gecko-...ed-simply.html

The motors you have are rated to stall at 187oz in. If your using your hand to manually stall the motor you will damage it if you continue to do so. You are also making the motor pull the maximum amount of amps they can handle so heat buildup will be VERY high. Please use extreme caution when doing so. I provided a snap shot of your motor specs from the manufacturer, and after reviewing them I have to ask why you would use a power supply with only 4.5a of current? The spec sheet reflects 4.24a per phase.


I would use a larger power supply.

The spec sheet also reflects the stall rating in bipolar configuration to be 264oz in.

Vince
Edealers Direct



Attachment 229828

[pmurdock]

Thanks for the response! I had the ammeter on the power supply and even with me moving it with my hand the supply current never got about 0.8 amps.. Shouldn't the amperage increase as the load on it increases and it tries to compensate and keep it in its place? From your article I understood that it will only pull as many amps as it needs to maintain holding position, but if I try to turn with my hand the amperage never gets up to the expected 4.24 amps per phase..

When you say a larger power supply - just more current and not more voltage is what I understand.. This is a 2 phase hybrid step motor.. but 1 phase is really only active at one time is it not? so shouldn't a 4.5 amp power supply be sufficient to cover a fully loaded phase, while the other one is inactive.. If I'm wrong on this then a 9 amp power supply would be needed at a minimum to give it the power it wants..


cheers!
Paul

[ger21]

The motors you have are rated to stall at 187oz in. If your using your hand to manually stall the motor you will damage it if you continue to do so. You are also making the motor pull the maximum amount of amps they can handle so heat buildup will be VERY high

Actually, steppers are rated for holding torque, not stall torque. And moving that shaft by hand won't hurt the motor at all.
Steppers are not like regular DC motors. Moving the shaft or stalling them doesn't cause them to draw any more current. Steppers don't draw current based on load.

According to Gecko, step motors will use no more than 2/3 of the rated current. If the motor is rated at 4.2a, then the most it will need is about 2.8 amps. Most of the time, it will use less.

So, you're not hurting the motor doing what you're doing, and the power supply is big enough.

The question is how are you turning the shaft? with 4 amps, you'd have a max of about 250oz, which is about 15.5 lbs. the motor should be able to hold a 15lb load 1" from the shaft. If you put a 4" wrench on the shaft, it would take less than 4lbs of force to turn it. It's really not that difficult to turn a motor like that. And keep in mind that the faster it spins, the less torque it has, so it';s also not going to be too difficult to stop it.

[storm2313]

Ger21, from what I understood he was turning the motor in the "opposite direction" meaning he exceeded the stall torque. Stepper motors are not designed to be put in applications where the stall torque rating is exceeded. If I misunderstood him I stand corrected however please follow the links I provide which directly show stepper motors draw current based on the loads they are applied to move.

Here's a video reflecting the Z axis requiring more amps due to the weight of the spindle. https://www.youtube.com/watch?v=ULUjwDM4MiM

Here's a snap shot of a tutorial on stepper motors located hereStepper Motor and Controller Primer - Phidgets Support that once again explains the correlation of how steppers draw amps as required to motivate a load.

Here's the snapshot. Attachment 229880

The power supply Paul is using is rated at 4.5a, and the steppers are rated to 4.24a per phase. That being said I would have at least an additional 10% due to variances.

[pmurdock]

I wonder if my gecko 202 drive is faulty then, because measuring current from the power supply V+ side it only ever draws < 1amp even under strain..

cheers,
Paul

[jfong]

The geckos are PWM type drives that switches the output FETs at around 20,000 times a second to regulate the stepper motor current. You won't be able to measure the maximum current with a inexpensive multimeter. You will need a oscilloscope or a maybe a very good trueRMS meter.

[ger21]

Ger21, from what I understood he was turning the motor in the "opposite direction" meaning he exceeded the stall torque. Stepper motors are not designed to be put in applications where the stall torque rating is exceeded.

Again, it's holding torque, not stall torque. If the motor doesn't have enough torque for the application, it just won't work, as it'll stall all the time. It won't hurt the motor, and won't draw too many amps. The drive regulates the current.

The power supply Paul is using is rated at 4.5a, and the steppers are rated to 4.24a per phase. That being said I would have at least an additional 10% due to variances.

And again. Gecko states on their website that his 4.2amp motor will never draw more than 2.8 amps (2/3 rated) when using a Gecko drive. Most of the time it will draw a lot less.

[jfong]

Also I have a couple old gecko202 drives on my gantry. I do notice the drive does go into current reduction mode pretty quickly when there no input stepper pulse. Keep that in mind when trying to rotate the shaft when it isn't spinning.

You can disable auto current reduction with jumper setting.

[pmurdock]

Yes.. measured this on a Fluke 289 TrueRMS meter.. I'll double check my measurement again.,. Just got a new Gecko G210X drive in case my old one was bad.

Ok Just did measurement.. this time I took video proof of it.. Also I took a video of how easy it is to rotate the shaft with the holding torque on the motor..

I did some calculations.. my motor is supposed to be able to support 284oz/in holding torque... or in metric.. 13.5KG-cm.. so found that average manual torque that can be applied by someone's hand is around 60lbf or 830KG-cm.. so then according to this my hand can apply WAY more torque than the motor can hold.. How does that make this motor useful for anything??? I want to hook this up with a belt to drive a rusty old fake cow for a roping unit.. so if this fake cow weighs 60lbs on a track this motor is worthless then..

I still think my current is way to low.. Also AUTO CURRENT REDUCTION IS OFF

http://youtu.be/IHxBEvBts9Q

http://youtu.be/Uv4NDSJtTDg

[pmurdock]

Here's a view of the voltage waveform @ 20kHz going to the motor windings

It doesn't change when I try to force the shaft to move.

Bear in mind I can start this motor up and it takes NO EFFORT at all to stop the shaft spinning.. I would think it should be more difficult than that.. Possible bad motor? I guess I need to measure resistance through coils.. will do and will return and report





Cheers!
Paul

[Dylwad]

Looks completely normal to me. If you need to move a 60lb load at a reasonable speed your going to need a MUCH bigger motor. What you have would move a 60lb gantry driven by a leadscrew with a lot of mechanical advantage and precision just fine, but I wouldn't expect more than a few hundred inches per minute speed.

[pmurdock]

Additionally I measured the resistance of each winding on the motor and it reports 1.2 Ohms which is pretty close to motor specs at 1 Ohm +/- 10%

[pmurdock]

I guess my question should be then - if not stepper.. then what for a simple start it up, spin fast (be able to control speed), and then turn off with a trip switch.. I am using an Arduino Uno to manage the setup.. with pots to control out speed, in speed, etc. Seemed easiest with steppers.. is there a better way?

that fake steer needs to take off quick and then after you've roped it, come back nice and gentle for me to rope again..

cheers!
Paul

[Dylwad]

Vfd driven 3 phase induction motor in the 2+ HP range comes to mind, since you don't really need fine control over position, and the speed, acceleration and reversing could all be done with an arduino and some code talking to the vfd.

Probably cheaper options out there though...but it will take some grunt to make it a challenge to rope.

Do you have an air supply? Maybe an air cylinder and pulley system, and a few valves (think aircraft carrier catapult on a much smaller scale). How far does the thing have to move?

[jfong]

You have better test equipment than I have!! Nice. Ya it doesn't take much to stop or rotate a 300oz-in stepper when you have a gear attached to the shaft. That gives you a lot more mechanical advantage. With my 276oz steppers with a geckodrive, it is very difficult to stop the bare shaft with my finger tips when the motor is spinning less than 200rpm. I use big servos and industrial drives from AMC when I really need high torque. That gets pretty expensive but can get really good deals on eBay if you know what to look for. Kollmorgen, yaskawa and parker are also some companies that make big industrial brushless servo motors/drives that can be interfaced to a Arduino. Some of them have step/direction inputs but most are analog +-10volt.

[storm2313]

The research I've done on stepper motors has been extensive, both in theory, and real world applications. These snapshots reflect the definitions correctly applied to stepper motors when used in robotics. A CNC by design is essentially a manufacturing robot. I agree the drive regulates current, but considering a stalled motor is generating the maximum current supplied by the drive doing it for long durations are very risky considering the amount of heat generated. I would recommend against it for long durations.

The snapshots I provided are provided by three different internet sources.

Attachment 230114
Attachment 230116
Attachment 230118

[ger21]

I don't believe everything I read on the internet, especially when taken out of context. Also from Wikipedia, directly following what you quoted above.

The maximum torque an electric motor can produce in the long term when stalled without causing damage is called the maximum continuous stall torque

This does not apply to steppers, as they do NOT produce their maximum torque when stalled.

Stall Torque - The torque a stepper motor requires when powered but held so that it does not rotate

I'm not sure what this even means??? Does it mean it's trying to rotate, but it's stalled? If it's commanded to rotate, it will stall. Right before it stalls, it will have nearly it's holding torque. As soon as it stalls, it will have far less.

[awerby]

While it's possible to use a motor to generate current, a stalled motor isn't going to generate any. It might be drawing current, but that's different. Stepper motors, as has been pointed out to you, don't burn up when stalled, unlike regular motors. The Wikipedia article you quote above is talking about regular motors, not steppers. The second quote is similar; it's talking about Pulse Width Modulated motors, not steppers. The third quote makes no sense at all - is that the one you wrote yourself? A stepper motor doesn't "require" torque; it produces a certain amount of it, which can vary with RPMs.

[storm2313]

The third quote comes directly from this site on robotics. How to Build a Robot Tutorials - Society of Robots

Please remember to be respectful when posting. I mean no disrespect, but am posting what can be researched by anyone using Google.

Please read it as it's directly stated towards stepper motors. The stepper motor may not burn up, but the driver will be producing an enormous amount of heat which can damage it. I'm sure you agree. Why risk it??? I don't know what your honestly talking about as I never posted anything about "requiring torque".

Please refer to the link provided for the definition breakdown posted.