Monday, April 28, 2008


First tests of the Haydon linear actuator stepper motor

The linear actuator stepper motor that I acquired arrived today. I slapped it on to the Tommelise 2 Big Board and it ran immediately without complaint.

What you see here is the board cycling it backwards and forwards for 240 steps with a 7 msec interval. It transitions at a rate of roughly 14.5 mm/sec at that setting.

In that it is like the other tin can steppers I've been working with. It can be made to run as fast as 17 mm/sec, but not reliably. A 7 msec interval is the fastest setting that it can operate at and deliver substantial force with no skipping.

The really amazing thing about this tin can stepper, however, is that it is dead silent. As you can recall from other videoclips I've posted the microphone on my camera is incredibly sensitive and made previous steppers and gearmotors I've taped sound very loud. This one you simply don't hear at all.

Mind, that is double what Darwin is currently achieving and means that it can print a maximum of roughly 0.8 kg of plastic in 24 hours.

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what is the model of that motor? also, what was the price?

also... darwin is currently limited by the extruder speed, not the speed of the motors. i can easily run my darwin XY head at a feedrate of 5000mm/minute (83mm/sec)
"what is the model of that motor?"

If you bought it off the website, it would be a 26844-12. That means that it uses 12v and transitions 0.102 mm/step.

"also, what was the price?"

One-off in the US, that one costs about $100 with a 12 inch travel lead screw.

Before you freak out you have to remember that all you need, once you have bought one of these, is to bind one end of that lead screw to your axis table and the stepper to either your printer baseboard or whichever axis table it's working from. The only thing that you have to include besides the axis table is the guide rails that it sits on. The stepper includes the lead screw and an antibacklash thrust collar.

I explored the volume pricing with Haydon last week. At 100+ the price of this sort of thing drops down to $20-30. That means that they are still making money at that rate.

What that tells me, from my experience with Annie's Darwin stepper, is that if I buy them direct from China or India that I am going to be able to do an axis for about $20-30, shipping included.

"i can easily run my darwin XY head at a feedrate of 5000mm/minute (83mm/sec)"

No question about it. The way Adrian and Ed designed Darwin you can get some enormous transition speeds. Similarly, Chris (nophead) has already printed at 16 mm/sec and seems confident that he can print at a lot higher speeds than that.

Remember, I, too, used to have dreams about big, very fast printing. Think about Godzilla.

Running a Tommelise 2, Darwin or McWire at just 14.5 mm/sec lets you print about 800 grammes of plastic/24 hours. That means that you could print a set of Darwin parts in 2-3 days. As I discovered with Godzilla, when you run really fast (I was hitting 25-35 mm/sec with the rig I had), all of a sudden you start worrying about the framework deflecting when you make a sudden change in direction for the print head.

What that means is that the rigidity of the cartesian robot gets to be very critical as the speed goes up. Keep that in mind and look at the Darwin frame. What's going to happen when you run the print speed up to, say, 50 mm/sec, print a 50 mm road and skip over half a mm and then print another 50 mm road in the opposite direction? Think about a diagonal infill in which that sort of thing is the order of the day.

My guess is that Darwin, which prints brilliantly at 6-8 mm/sec is going to shimmy like a washing machine in spin cycle with your running shoes in it.

That's NOT a criticism of Darwin, mind. I don't think Ed or Adrian had in mind running Darwin much faster than it is being run already. It's wonderful when you operate it within it's design parameters.

I get back to basics, though. 800 grammes of plastic is a LOT of plastic filament to burn through in a day for a person like you or me. If you want to double output, it's probably better to just use Darwin to print a daughter Darwin than to design a much heavier, more rigid system that can operate at twice or ten times the speed. :-)
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