Running Different Voltage on Steppers (Rambo or others)

[Demolishun]

A few years ago myself and a friend built a plasma table using a hand plasma torch, stepper motors, some stepper drivers (Gecko), and a 4'x4' metal table.

We found out that running at higher voltages and low current (within wattage rating of the steppers) we could get more rigidity, speed, etc. We still run that table at about 70VDC. It has been upwards of at least a 7 years. So I know it can run long term just fine.

So, is there a way to increase the voltage on the Rambo controllers? I know the Max runs them at 12VDC. But I would down the road want to look into running the motors at higher voltage and less current.

[Captain Starfish]

From what I've seen the Rambo has separate rails and inputs for the heaters vs controller board. In the RMax we just wire 'em all into the ATX output at 12V but some guys are running at least 24V into the heaters with good results. Don't know how high you can go. Don't know if you can do the same with the stepper power, either.

First question I'd be asking, though, is:

"Why?"

The extra rigidity, speed, etc come from being able to push the steppers faster and with more load before they begin to skip.

I haven't yet seen a stepper (running 12V) skip on my RMax unless I've done something catastrophically stupid. And in that case I want it to skip rather than snapping an arm or cracking the bed because the motors are now strong enough to hulk out and smash the printer to bits.

Speed isn't limited by the steppers on these things, it's limited by other things. Most notably the balancing act of hot-end temperature between cooler = won't allow flow past a speed vs hotter = too much ooze, sagging prints, lift issues and even burning plastic. Given a particular choice of filament there's a fairly narrow temperature range (and thus hot-end viscosity / back pressure / max flow rate) that will work. That's the limitation which drives your printing speed. And, within that limitation, 12V on the steppers is ample.

Absolutely agree on the principle - my DIY CNC mill would have been a lot more useful if I'd been running 100V through the motors than the crappy 24V I had available to me at the time. But, for this application I think it's a solution to a problem that doesn't exist.

[Polygonhell]

My guess is that the logic portion of the board isn't good for anything over about 15V, you'd almost certainly have to power the 5V logic from USB at much more that that, and there is almost certainly a weak link in the system before you get to the stepper drivers.

Technically the drivers themselves will tolerate something like 38V (you'd have to look at the manufacturers data sheet for the actual value) , though you'd likely have heat issues and the drivers die if they are taken over that voltage even instantaneously. The last part is why you are told not to unplug steppers while there is power to the board it's enough to cause transient voltage in excess of the rated maximum.

Most printers don't run their steppers at anything like optimal voltage, but they don't really need to. 12V is enough to run most printers fast enough that other mechanical issues come into play before the stepper limitations are reached.

[Demolishun]

You are right. Maybe this is not a good application for this. I forget my plasma cutter is like %99 carbon steel tubing. Good point on the extra torque might cause issues with the framework. I am mainly electrical so I tend to assume some things.

I thought I saw things on this like missed steps because of torque in some of the posts. Maybe the issues are less because the motor is not actively ripping things apart.

BTW, we are considering retrofitting our plasma cutter to use a big extruder and print giant stuff on the 4'x4' area. Not tall, just big.

[Captain Starfish]

I think most people who complain of "skipping" aren't talking about the motors skipping, rather, the pulleys are skipping in the belts because the belt tension is too low.

4x4 big extruder sounds great!

Even better: get a MIG torch on there with a little computer control over the wire feed and have yourself a metal printer.

[Demolishun]

Even better: get a MIG torch on there with a little computer control over the wire feed and have yourself a metal printer.

Ooh, I will talk to my mechanical engineer friend and see what we can do. That does sound like fun!

I did think of one thing running a non-standard voltage "might" be useful for. Perhaps reducing current might change the harmonic response and reduce vibration? However, using motor isolator gaskets might be a better solution there. But maybe there is a some fine tuning that can be done for the really OCD among us...

[Captain Starfish]

When I say "computer control" on the wire feed, you will probably need to replace the wire feed motor with a stepper. Given how much pressure is placed on filament in a plastic printer, I wouldn't be surprised if the bog standard EZStruder stepper and RAMBO driver had enough grunt to feed the wire.