MegaMax was a great 3D printer, but it was time for some changes. He was difficult to transport because the electronics were in a separate housing with many cables to disconnect and reconnect, barely fit through doorways, and required a positively gargantuan enclosure to keep the temperature up to control ABS delamination. Though it hurt to do it, I tore him apart and did a complete redesign/build into a form that is more like what I would have done had I known anything at all about 3D printing when I started building MegaMax.
I reused what I could including a lot of the 8020 extrusions in the frame, the Z axis screw assemblies and drive belt, and the X and Z axis motors.
ball screw drive Y axis with high torque motor- precise but noisy
linear guides in X and Y axes instead of 1/2″ round guide rails and linear bearings
SmoothieBoard controller instead of Arduino/RAMPS
BullDog XL extruder and E3D v6 hot end
RepRapDiscount graphic LCD control panel
narrower frame design without giving up print volume- easier fit through doorways!
polycarbonate panels to enclose the print area yet provide a clear view of the print
electronics in a drawer for easy service and transport and neater appearance
DSP motor drivers and 32V power supplies for X and Y axes
Liberal use of screw terminals to make servicing easier
Modular X and Y axes that can be removed for service and replaced in minutes.
SoM will be making his public debut at the Milwaukee Makerspace very soon…
32V Power supply for Y axis motor. No regulation necessary!
Smoothieboard is supposed to read the config.txt file from its uSD card (conveniently accessible via USB) every time it boots. That makes changing configuration very easy and fast – all you do is edit the config.txt file, save it , and reboot the board. Firmware is updated the same way. With the ATMega2560 you have to find the configuration variables by searching through multiple configuration files, make the necessary changes, recompile the firmware, then flash the controller. I said the SmoothieBoard is supposed to read the file every time it boots, but it wasn’t doing it. I’d make changes and they would not appear in the behavior of the printer. Hmmmm.
Layers kept shifting in the X-axis- I expected Y-axis problems, but not X!
I attempted some prints and managed to get two decent ones in about a week of screwing around with it. I tried dozens of combinations of speed, acceleration, junction deviation (smoothie-speak for jerk) and even tried different slicers. The machine went completely nuts on two occasions and ignored the Z-axis limit switch and slammed the extruder into the print bed, gouging through the Kapton tape and into the aluminum! I decided I needed some professional help so I got on the #smoothieware IRC channel and discovered that the developers of the board/firmware hang out there quite a lot. After a lot of back and forth Q and A and testing someone suggested it might be the uSD card causing the problem. I picked up a new card at Walmart, put the firmware and config files on it , booted the machine, and attempted a print. PERFECT!
The new uSD card worked! The small round post is 4mm diameter.
I have made several prints since last night and they have all come out fine. I still have a little tweaking to do and to test the limits of the machine’s performance, but I think the problems are behind me.
Next up: X-axis redesign/build. I’m replacing the two guide rails with a single linear guide. I have also ordered and received a BullDog XL extruder to replace the hacked up QUBD unit I’ve been using. I’ll be adding a DSP driver and 32V power supply for the X-axis motor, too.
After that, I have some ideas for a filament respooling machine and ways to fix the retraction problem in the SnakeBite extruder.
I installed the Y-axis screw drive in MegaMax using the old NEMA-23 stepper motor. A couple really good things came from this:
1) I can now adjust the bed leveling screws from the underside of the bed using thumbwheels instead of a screw driver. I know, I know, everyone else in the world has been able to do this from day 1…
Thumb screw for leveling print bed. Screw is threaded into teflon block.
2) Unlike everyone else in the world, with fully supported linear guide rails, the print bed does not move in any direction but along the Y axis. In the old scheme, with the end-supported round guide rails, the rails would flex and the bed would move up and down when applying pressure to it (sometimes even the screw driver pressure to adjust the bed leveling screws). Now, if the bed moves at all in the vertical direction it’s because the bed plate (1/4″ aluminum) itself is flexing!
A couple bad things were also discovered:
1) The vibration and noise problem I was hoping to solve has not been solved. It has been made worse, though the character of the noise is improved to musical tones instead of just harsh buzzing and rattling.
2) Several failed test prints at ever decreasing jerk, acceleration, and speed settings have demonstrated that the old motor simply doesn’t have enough torque to drive the screw reliably at reasonable printing speeds.
Shift occurred in Y-axis due to insufficient motor torque.
Further research into the first problem indicates that the vibration and noise are inherent in using steppers, and worse in MegaMax than in machines that use NEMA-17 motors because of the higher detent torque in the NEMA-23 size motors. Detent torque is the little bump-bump you feel when you turn the motor shaft by hand. The solution to the problem is to use a good driver for the motor and a higher voltage power supply. The little A4988 chips in the Pololu drivers on the RAMPS board are very unintelligent- all they do is provide microstepping. They work OK for NEMA-17 size motors because of the speeds and low detent torques in those motors. When used with NEMA-23 motors the driver limitations become apparent – as they have in MegaMax- lots of noise and vibration.
Good stepper drivers are DSP based and automatically sense resonance and damp it electronically. They use phase controlled sine wave currents to drive the motors smoothly. Fortunately, DSP stepper drivers for NEMA-23 size motors are pretty cheap. Here’s video of the DM542a driver pushing a NEMA-23 motor around. I have ordered a DM542a driver.
The best power supply for stepper drivers is not a switcher, and running steppers from a switching supply will often result in a dead power supply. I will be building a simple, unregulated transformer, rectifier, and filter cap supply to go with the new driver.
Next came the question of how to determine how much torque is needed to properly drive the Y-axis. A bit of research took me here: Motor size calculator. You just select the scheme for which you want to size the motor, enter the appropriate data, and it magically tells you how much torque you need to do the job. When I ran the numbers on MegaMax, it told me that I need about 350 oz-in of torque (about double the torque of the motor I have). I did a quick search and found a Chinese made (of course) 425 oz-in motor for $50. Also on order…
The motor mount I am using is designed for a NEMA-34 size motor with which I use an adapter plate to allow the NEMA-23 motor to fit. Since I’m buying a new motor anyway, why not just get a NEMA-34 motor? It turns out that the best stepper for the job is generally the smallest motor that can provide the necessary torque. A NEMA-34 motor could provide much more torque but the detent torque and rotor inertia would work against smooth and fast operation, and require a bigger power supply.
Back side of MegaMax showing motor mount, adapter plate, flexible coupler, and drive screw in Y-axis.
The ATmega2560 and RAMPS boards will be replaced by a SmoothieBoard. It has a much faster processor, much better connections for motors/external drivers, etc. It currently lacks an easy way to add an LCD controller, so I may have to connect to a computer to start prints up (it has ethernet and a built in web server so it can be accessed from any computer on the network). When a clean way to add an LCD controller becomes available, I’ll add it. SmoothieBoard review
MegaMax has been and continues to be my main project for the last 2+ years. I am currently working on some upgrades that will make him more Mega and even more Max. The Y axis is being converted from belt drive to screw drive and the round guide rails are being replaced with linear guides and bearing blocks. The X-axis will also get converted to linear guide and bearing block and change from 5mm pitch belt to 2 mm pitch belt drive. I feel confident saying that once these modifications are complete the flaws/errors in prints will be due primarily to the nature of liquid plastic squirting through a nozzle, not positioning system errors.
I recently updated my web site with a sort of historical look at the project, including all the mistakes I’ve made along the way and the often failed attempts at correcting them. Here is the page that shows how it all started, how it has ended up, and where it is going. http://mark.rehorst.com/MegaMax_3D_Printer/index.html
As part of my effort to reduce the noise and vibration in the Y axis, I am going to try using a screw drive instead of the 5mm pitch belt. I rescued a screw drive assembly from a big XY table but it uses a 200W servomotor for which I have neither power supply nor drive electronics. Never fear! The motor was a NEMA-34 size, so I designed an adapter to mount the NEMA-23 stepper that MegaMax uses in the NEMA-34 motor mount. Next I needed a shaft coupler- the screw has a 9mm diameter attachment and the NEMA-23 motor has a 1/4″ shaft.
Adapter plate on NEMA-23 motor
I used DesignSpark Mechanical to design the motor mount adapter and flexible shaft coupler. I uploaded the motor adapter to Thingiverse (http://www.thingiverse.com/thing:526424) and it proved surprisingly popular so I designed another that adapts a NEMA-23 mount for a NEMA-17 motor (http://www.thingiverse.com/thing:526443). I had to make two attempts at the flexible shaft coupler- the first design proved a little too springy and flexible, so I tried again with a more beefy design. It turns out it is pretty easy to design this sort of thing in DSM. I probably spent 30 minutes on the first one and about 10 minutes on the second one.
I sliced in Cura because Slic3r was having some problems. The prints look a little rough because of all the support material required to print the springs, but they work fine.
Flexible shaft couplers- not-so-springy and super-springy.
Adapter and shaft coupler on motor
Motor mounted on screw assembly
I’ll post an update when I get the screw mounted on the machine.
Several months ago, a humorous request went out for a Zamboni that could be used on the Nerdy Derby track.
Last year the Milwaukee Makerspace held a Maker Fest and a Nerdy Derby track was made for the occasion. The design allowed the track to be disassembled in 4 foot long sections.
When the track was reassembled, earlier this year, for the South Side Chicago Maker Faire, it was found that the joints did not match up as well as when it was first put together. Small ledges, that went up and down, would cause the cars to bounce off the track or hit the bottom of the car. Both of these scenarios prevented the cars from traveling freely down the track.
As many of you know, we just had a GREAT Maker Faire here in Milwaukee last month and the Nerdy Derby track was needed again!
We produced, and ran, over 1000 Nerdy Derby cars over the 2 day event. Wow!
A month or so before the event I started working on an idea for a Zamboni type of device. My first thought was of a custom contoured planer that could be used at each joint to smooth them out. This idea seemed like too much work so I proceeded forward with my second design. This consisted of a simple sled hat used a drum sander, which smoothed out the high spots. Wood putty was then used to fill in any low spots.
We’re planning on setting up a Nerdy Derby track at the upcoming Maker Faire Milwaukee so to that end we are preparing car parts. We recently received a generous donation of filament from Inventables (thank you!) so MegaMax and others went right to work printing wheels for the Nerdy Derby cars. The goal is to print 4000 (!) wheels before the Maker Faire.
A small batch-test run of twelve wheels
Starting a batch: printing 40 whimsical wheels and once!
I repaired the Budaschnozzle hot-end over the weekend and bolted the SnakeBite extruder to it and then to MegaMax and tested it last night. There’s plenty of tuning to do, but the first print looks promising:
When I recently was at the thrift store and saw a pair of ice skates next to a kick-scooter, it got my mind going. “What would a scooter look like with skates in place of wheels!?”
The next time I was at the Makerspace, I saw my old electric scooter over on the Hack Rack. This was a scooter I originally rescued from a dumpster. Although it didn’t have batteries, just adding power and a little tinkering got it up and running again. A few of the EV Club and PowerWheels Racing guys played around with the scooter a bit, but eventually the controller got toasted, and who knows what happened to the front wheel.
Oh well, I’d be replacing that front wheel with an ice skate anyways.
Turns out that the heel of an ice skate is actually sturdy enough to drill right through and use as a mounting point. I simply drilled through the skate, inserted a spacer, and then ran a 3/8″ bolt through the skate and the front fork of the scooter. I finished it off with a couple of washers and a nut.
Then next thing to fix was to get the motor going again. Turns out that it’s a brushless motor. While I have a fair amount of experience now with BRUSHED motors, this was my first experience with brushless. I did a little research, and then ordered a 24V, 250 watt generic brushless controller from a mail-order scooter parts company. Unfortunately, it used a different style of throttle than what was already on the scooter, so I had to order a throttle to match.
Connecting the controller was pretty easy, three wires to the motor and the black and red one to power. I first bench-tested it with an old printer power supply, and once everything was working right, bit the bullet and bought a brand new pair of 12ah SLA batteries. The two batteries are wired in series, along with a 20 amp fuse, and then go to the controller.
I still needed a deck for the scooter. I dug through some scrap materials and found a pair of cabinet doors that were about the right size. I cut them down just a bit and bolted them to the scooter. I even re-mounted a cabinet door handle to have as an attachment point for towing a sled.
With that, I was ready to go for a test ride, so it was off to the lake. Once I was on the ice, I turned on the scooter and gave it a go! What fun! It really zipped along, but it was almost impossible to steer, as the back tire would slip right out from under me! Time for more traction!
I decided to make a spiked tire. I removed the rear wheel, then disassembled the two-part rim and removed the tire and inner tube. I stuck 1/2″ self-tapping, pan-head, sheet-metal screws through the tire from the inside, so that their points stuck out. I evenly spaced out 24 screws and alternated them to be slightly off-center side to side. Next, I put some old scrap bicycle inner tube over them as a liner to protect the scooter tire inner-tube. After that, it was just a matter of reassembling everything.
Now for test #2 out on the ice. Remembering how much it hurt to fall on the ice, I was prepared this time by wearing my motorcycle jacket (which has padding built-in) and my helmet. Good thing too, as I would learn while steering with one hand and holding a GoPro camera in the other…. (Note to self, keep both hands on handlebars at all times.)
Overall, the Ice Scooter works great! I still have a few little things to do on it. For example, the motor is running “sensor less”, and I’d like to learn about how brushless motors use the sensor system. I’d also like to get a small 24V dedicated charger. As it is right now, I have to remove the deck and manually charge with a little 12V charger.
From thrift store idea, to hack rack, to life on the ice, it’s always fun to see what you can do with just a little ingenuity. I hope you like this project. If you want to see more on it, please check out the write-up I did on Instructables. It’s even in a few contests there, and I’d love your vote!
Keep on Making,
At Wisconsin State Fair Park, the same weekend as Harvest Fair. Admission is free. Thanks for a great 2015! See you next year. A joint presentation by the Makerspace and the Betty Brinn Children's Museum.
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