Really Low Stepper Motor Torque

I was able to get all of my stepper motors wired today and tested using the LCD display. But, unfortunately it looks like I’m getting really low output torque from the motors. I first noticed this on the Z axis, as it was hardly enough to lift the gantry, but applying minimal resistance to any axis is enough to stall the steppers. The steppers I’m using are recycled from an old cheap Chinese printer kit, so I wouldn’t be surprised if this is the root of the problem. But either way I wanted to check in here before I order new stepper motors. Does this seem like a likely cause for issues or is there something else going on here? I’d hate to spend $50+ on new motors only to find I’m having a board (Ramps 1.4) or power supply (12V 30A) issue. I appreciate the help! :slight_smile:

You should have plenty of power to work with.

Are your motors wired in series? Dont use the 2 Z connections on the RAMPS board, they’re wired in parallel so you need double the amperage to get the same torque. Series wiring gets you best torque per amp from the drivers. There are instructions in the forums to make a simple series wiring harness.

Have you checked the current on the drivers? Measure dc volts between the trim pot and ground and you should get in the neighborhood of .7 volts. These may have been set lower for the previous machine.

Hey Tom, I actually tweaked Marlin so that both Z axis motors use their own drivers. One is using the original Z axis driver and the other is using what was E1. I did check the trim pots on both and they were reading around 0.8 volts.

One thing I did see digging around the forums is that the gantry should fall under its own weight when powered down, which isn’t quite true for me. I can get it to fall with some assistance. Maybe this additional force is where the problem is coming from?

Out of curiosity roughly how much physical resistance is normal to stall the motors? Even on the x and y axes, it doesn’t seem like it takes very much. If I had to guess maybe a pound or two (Ill have to see if I can find a way to actually measure it).

I was able to hang a 1kg of olive oil from a string, attached to the gantry, then slung over the side of the table.

Extra virgin?

@alexzenk - I don’t have a LowRider myself so I can’t speak to the mechanical properties of the machine. I have used a variety of control boards and stepper drivers, so I’m not bashful about sounding off on those topics.

What’s the stepper motor torque rating?

Sorry, we used them all getting the 3/4" EMT Primo design working. But we do have an extra goat… :goat:

I wasn’t sure if it could handle it, so I used the extra light. It comes in a plastic container instead of glass.

You don’t get it in lead-soldered tin containers straight from Italy? No wonder your veal piccata tastes like McNuggets with rabbit turds… :wink:

Haha I’m quite certain I wont be lifting any jugs of olive oil at this point, no matter how light–it sounds like I’m missing steps even under its own weight.

And @highprobabilit…that’s a great question! I spent a huge portion of yesterday trying to figure out exactly that. They’re pretty much a mystery to me. I had assumed they’d be adequate based on the body size (I know the two aren’t technically coorelated). They came from a cheap Chinese printer kit and don’t have markings anywhere on them–so I have a feeling they’re rated lower than the manufacturer (whoever that is) wants to own up to.

I was actually able to find what I thought was a smaller stepper motor lying around and is rated around 60oz in. It’s not scientific, but running both in my setup, that one feels like more torque than the recycled ones. Definitely suggests new steppers will fix the issues I’m having…

measure the coil resistance of one of the motors and multiply by the current you have set, double it for 2 motors and see how close you are to your 12V supply.

Some steppers motors have very high coil resistance (10-30ohms) and will require lots of voltage to reach even .5A of current (5-15V).

Thanks for this tip! The wife and I were out of town this weekend but I’ll break the multimeter out after work tomorrow. I did end up ordering the recommended steppers, but it would be good to know if these are still good for a higher operating voltage (I’ve got a laser cutter project in mind sometime down the road they might be usable for…)