Ron's Compact Extruder, Mark III
Description
Version 3 simplifies the design a bit, and tweaks it to make a stronger print.
I left ulti_rcx_2.stl, along with the old sources here because I broke ultimaker support while redesigning it.
Version 2 addresses two issues I had with version 1.
1) Idler pressure was very touchy - as you increased pressure on the idler, it would put axial force on the motor's gearbox, which can't be good. I added a pocket for a 115ZZ bearing, to buttress the drive shaft.
2) I found that even with the bearing on the drive shaft, I have to run the motor hotter than I'd like, so I added a bracket for a 40mm fan.
Also, I split the extruder body into 2 slices, to make it easier to print.
Finally, thanks to canadaduane, we now have a variant which replaces the ultimaker's bowden extruder with a lightweight carriage mounted extruder.
P.S. ezmobius (actually, Triffid_Hunter) has designed a fan shroud to go with his extruder body which is better than the bracket I provided, so use the fan shroud from thingiverse.com/thing:24390
Instructions
1 Geared stepper motor (Minbea PG35L-D48).
1 Drive wheel (MakerBot MK7, Arcol 11x5, or contact blddk in IRC).
1 115ZZ bearing (5x11x4) (Drive bearing).
1 624ZZ bearing (4x13x5) (Idler bearing).
2 M3 x 25mm Socket head screws (Motor mounting screws).
4 M3 x 35mm Socket head screws (Idler mounting screws).
2 M3 x 20mm Socket head screws (Carriage mounting screws).
1 M4 x 16mm Socket head screws (Idler bearing hub).
8 M3 washers.
8 M3 nyloc nuts (At the very least, use nyloc nuts on the idler).
1 M4 nyloc nut (Idler bearing hub).
Motor sources:
eminebea.com/en/product/rotary/steppingmotor/pm/gearbox/pg35l-d48.shtml
mpja.com/prodinfo.asp?number=18840+MS (Mostly Identical to the motor which was previously available at All Electronics, including the vestigial gear. Drive shaft is shorter, so you won't be able to fit a bearing on the end of it.)
pollin.de/shop/dt/MzE1OTg2OTk-/Motoren/Schrittmotoren/Getriebe_Schrittmotor_NMB_MAT_PG35L_048_USC0.html (European supplier, appears to match the mpja.com motor.)
Drive wheel sources:
store.makerbot.com/mk7-drive-gear.html
indiegogo.com/mini-hyena (the 11x5 version).
contact blddk in #reprap irc.
If you purchase the motor from mpja.com, you'll need a small gear puller or faucet puller to remove the vestigial gear.
Assembly instructions:
Use your imagination, lacking that, refer to thingiverse.com/thing:22980 . Don't forget to install the drive bearing.
Firmware configuration
E-Steps/mm (These values will get you close; Calibrate further, or live with crap prints!):
makerbot Mk7 with 16x microstepping - 825.698
blddk hob with 16x microstepping - 761.328
I found that marlin's default settings for E feedrate, acceleration and jerk were all too high for these motors.
#define DEFAULT_MAX_FEEDRATE {400, 400, 220/60, 45}
#define DEFAULT_MAX_ACCELERATION {9000,9000,100,500}
#define DEFAULT_EJERK 1.0
Software configuration
Reduce your retract speed to 10mm/sec.
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I would stay away from a faucet puller on this one to get the gear off the PG35L. I barely got it off, spent half an hour doing it and ruined the faucet puller in the process because the threads were never designed for that much force.
I'm really impressed with the print quality you get with these. I have a few of these from All Electronics from a while ago and I had been planning to build an extruder with them, but I just stumbled upon your design. It looks great. I had done an initial design, but didn't really go forward with it because of the motor specs. The DC resistance is quite high (70 ohms according to data sheet), which is why all the heat. I tried driving the motor when I first got them but the heat and the fact that the speed is limited deterred me from further work... This type of motor is usually driven with a less intelligent driver, one that doesn't actively control the current (hence the high internal resistance.) The internal resistance is meant to protect the motor when a constant voltage is applied. This really isn't the type of motor that the Allegro chips are meant to drive (compare to the Nema 17 motors which are usually used which have only a few ohms of DC resistance).
Have you been able to take any temperature measurements? I'm really curious about the long term reliability of these. Do you have an estimate on the number of hours you have printed with these?
Great work.
As long as you use a fan or heat sink with them, they seem to be quite reliable. I've run 16 hour prints with them, without any difficulty, and without them failing the "thumb" test (i.e. I can hold my thumb to the motor without undue pain).
Without no fan or heat sink, they'll fail the thumb test quickly - they continue to run, but the heat will eventually soften the delrin gears enough to cause the drive shaft to slip out of alignment, which will then jam the gearbox.
I bought one of these, in single extruder configuration, direct from the source.
It came well printed, and awaiting me to screw in the two bolts pinning the mount, motor and shroud. All wires were molex'd and ready to plug in and go. The carriage mounting holes were narrow for the mounting bolts for my Eclipse hot end but Mr. Reamer took care of that.
My calibration procedure
.
Not knowing which pinch wheel I was supplied with I assumed an MK7 and set up as follows:
#define INVERT_E0_DIR true
#define EXTRUDER_MTR_STPS 48
#define BOLT_DIAMETER 10.56
#define EXTRUDER_GEAR_RATIO 35.45454545454/1
#define DEFAULT_MAX_FEEDRATE {500, 500, 5, 45}
#define DEFAULT_MAX
_ACCELERATION {9000,7000,100,500}
I then ran off 30mm in 5mm steps, measuring as I went. Each 5mm was a little large and by the time I got to 30mm I was measuring 32mm.
I got out bc and scale=12'd it.
32 / (30 / 10.56)
11.264000000000
I then updated to use
#define BOLT_DIAMETER 11.2640
I
ran off 50mm and got 50.04mm on my $10 HKG digital caliper, which read -0.04 when I ran it back to 0. So I'm calling that 50mm. :-)
His customer service may consist of "I help those whom help themselves" but he designs and builds one helluva an extruder. It's as small, light and strong as I'd hoped
. Not only did I get X axis build box, I also gained Z axis build box.
Well worth my money and time to upgrade to it.
It's hard to say how much from your photo, but it looks like the motors really cut into your max X axis travel. Have you considered rotating the motors 90 degrees? Maybe by allowing for them to be elevated above the belt via increased extruder or carriage thickness or designing a way for the motor and idler to be mounted lower respective to the axis?
Or (this would undoubtedly require redesigning your extruder) have the motors at an angle from the X axis just enough to clear whatever they might collide with until the carriage hits each end of the axis. The motors (in my vision) would be hanging off the same side (opposite the belt) with someth
ing like a 120 degree angle between them. This would be a relatively larger imbalance in weight on the carriage compared to a single motor hanging 90 degrees off one side, but realistically the axis is much stronger than needed anyway.
On my printer, with a single extruder installed, I can reach the entire 200mm of the X axis.
With both extruders installed, I can reach the first 180mm of the X axis with one extruder, and the second 180mm of the X axis with the other extruder.
So yes, with both extruders installed, it cuts into my build area a bit. I'm currently working on a vertical-x design with the intent of gaining
that build area back, and improving belt clearance at high Z values.
Be aware that the steppers from MPJA appear to have shorter drive shaft. I bought four of them and removed the gears using a nut splitter. The drive shaft is not long enough to even go all the way through an MK7 drive gear, much less into the bearing.
Wow, I'm really impressed. This is a nice piece of engineering. It worked well the first time--however, because I don't have the same size bearings as you do, I had to add a 14mm hole for a 608 Drive bearing. I like being able to use the same bearings in both cases (the Idler and the Drive) which I did. Here's that I added to more_configuration.scad in case others find it useful:
605_bearing = [5, 14, 14, 0, 5];
605_bearing_clearance = [0.4, 0.4, 0.4, 0, 2];
(And then change the relevant drive_bearing lines at the top of rcx_2.scad).
Thanks @raldrich!
Excellent! I'm printing the Ultimaker variant now and will report back with the results.
On another note, have you seen motor mount heat sinks such as this one [1]? I have one on order and intend to mount it to the motor and see if this alleviates the heat issue.
[1] http://www.ebay.com/itm/ws/eBa...
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amp;item=190681807867
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amp;ssPageName=ADME:L:OU:US:1123
It'd be interesting to measure it's temperature when printing with your heat sink vs the 40mm fan.
with some milling, and drilling you could screw a 20mm fan to it.
I was thinking about making a heat sink out of copper ribbon, folded to shape, but just blowing on the motor with a fan seems to be adequate.
License
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I checked with mpja and allelectronics and can't find the steppers. Is there another source for them?
Unfortunately, because these were surplus motors, they've become very difficult (if not impossible) to find. There were two variations that I came across, one with a 12mm drive shaft (which is the one this is designed for), and another with an 8mm drive shaft (which unfortunately, doesn't leave enough room for the drive bearing, which in my experience was required.
An alternative motor (which would require a different extruder design) would be http://trinitylabs.com/product..., and http://www.thingiverse.com/thi...