BotHacker

My previous attempt at building a heated build surface seemed like a success. Then Nophead came along and demonstrated beautiful results with his Kapton/high-temp approach (>100 C) which immediately made my work obsolete.   I couldn’t easily achieve temperatures that high without moving to higher voltages, which would then necessitate a redesign of my controller.

This time around, I’m trying the off-the-shelf approach:

• 4×4 flexible silicone rubber heater, 115VAC, with pressure sensitive adhesive on one side, ~$30
• Commercial PID temperature controller,  $42
• Type-K thermocouple, ~$6

It’s not the cheapest approach, but it should be a pretty simple system to get up and running, and produce more than enough heat for any printing scenario.

I haven’t yet tried the Auber Instruments controller, but if it works, $40 for PID control seems like a great deal.   For the baristas out there, they also sell a kit to upgrade your high-end espresso machine to PID temperature control — awesome!

Yesterday I finished assembling the z-axis and installed it on the support structure. This photo shows the bot pretty much complete, sans extruder and drive belts:

All in all, a pretty nice looking machine.

The z-axis is a self-contained unit, making it very easy to assemble and maintain:

I’ll be assembling the control electronics this week.

A few more pics from my RepStrap build:

Adding a build surface:

And then adding the gantry:

Somehow I ran out of T-nuts, so I’ll be working on other stuff until the parts arrive. Here’s a quick video showing the movement of the Y-Axis:

Just returned from a week of vacation -  time to get back to robot building!

A desk covered with robot parts is always a beautiful sight:

The 8020 stuff assembles very nicely, as you can see here:

All the flat parts were cut with a waterjet. I buffed the outside edges with a Scotch-Brite wheel, and reamed the close tolerance holes.  There were also a few holes that had to be tapped. Lastly, I pressed the bushings into their locations. All told, it took me about 2 hours of prep to get to the bolt-together stage.

Here’s a closeup shot of some flat parts:

More to come…

Here’s a couple screen-grabs of my latest RepStrap design built from 80/20 T-Slot aluminum framing and waterjet cut aluminum plate:

Orders went out a couple days ago, so I should have everything here next week.

Any suggestions for a name?  I’ve been thinking about “T-Rex”.

I’ve had a few questions about my electronics, so here’s a quick description of my setup.

Currently, the electronics for my RepStrap look like this:

The lower unit consists of a Seeeduino Mega with an expansion board of my own design.

The Seeeduino Mega is an Arduino Mega clone that incorporates a bunch of nice improvements, and is smaller and quite a bit cheaper. Since MakerBot is moving to the Arduino Mega for their next generation motherboard, it seemed like a good time to make the switch.

Here’s a closer shot of the board:

As you can see, I had to fix a couple missed airwires…

The board includes:

• 4 RepRap compatible stepper connectors
• RS485 comms
• E-Stop and buzzer connectors.

The board is powered by the USB connection.  The board does not have the “powered” RJ45 connectors for RS485 used on the standard motherboard.  Instead, it just has a simple header for the AB connection, which is more in line with the Mendel approach.

I’ve included a fourth stepper connector so that the extruder can be driven directly from this board, rather than the roundabout way that the Mendel uses timing wires between motherboard and extruder.   Also, the stepper connections incorporate additional control lines that can be used to select stepping or sleep modes on the stepper drivers.

I’ve tried to keep the board compatible with RepRap/MakerBot.  This board currently runs the latest MakerBot Motherboard 2.0 (Mega) firmware with no change.

For the stepper drivers, I wanted to see if an EasyDriver could be used as an alternative to the MakerBot drivers.  So I created a breakout board for four of them:

The board incorporates RepRap compatible stepper connectors so it can be used with any current RepRap motherboard.  It also has RepRap compatible stepper connectors, and a PC power connector (Molex).

Since the EasyDrivers are microstepping boards, I’ve also included jumpers for the MS1 &MS2 lines which can be used to select the step size (1, 1/2, 1/4, or 1/8).  Alternatively, I’ve connected these lines to extra pins on the stepper connectors, so these can be controlled by the Host.

The fourth stepper socket was included for a future stepper driven extruder.

So far, the EasyDrivers seem up to the task.  In fact, I’ve been running them with the current set way below max, for smoother running.  The Mendel appears to be similar in size and mass to my RepStrap, and uses full ball-bearing axes, so I’d think the EasyDrivers would work well for the Mendel.

If there is any interest in these boards from the RepRap community, I’d be happy to make the designs available, or even get some boards made.

Also, any feedback on the design or overall approach would be greatly welcome!

I’m jumping on the heated platform bandwagon:

With 4 x 1 Ohm power resistors the output is around 36 Watts. Testing has shown that it will hold 60 C at at 70% duty cycle (178 pwm) — too hot to touch for more than an instant.

I’m driving it with my Arduino Pro Mini-based temperature controller, shown here:

This board provides two channels of thermistor based PID temperature control.  The sensor and driver circuits are borrowed from the RepRap extruder controller.  The controller will run stand-alone using pre-set temperatures, or will respond to Gen3 protocol commands over RS485.

It includes a standard PC power connector (molex) for easy RepRap use, and jumper selectable RS485 termination.

When I complete the move to a stepper driven extruder this board will control both the extruder and platform heaters.

My dabbling with Eagle has started to yield some results:

On the far left is a shield for the Seeeduino Mega that turns it into a RepRap motherboard. The Seeeduino (above the board) is a really nice Arduino Mega clone.

In the middle is a temperature controller board for an Arduino Pro Mini 328 (also shown above the board).  It will provide thermistor based PID temperature control for two heater elements, and uses RS485 for communication.  The sensor/drive circuit is borrowed from the RepRap extruder controller, and the firmware will be running my PID temperature code.

And on the right is a carrier board for four EasyDriver stepper drivers (one shown at the top).

I’ll provide more details after I finish assembly.

As part of my push to improve print quality, I’ve been experimenting with microstepping. The SparkFun EasyDriver boards look like an interesting alternative to the standard RepRap driver boards.  They only drive 750mA compared to the 2A for the RepRap boards, so they may turn out to be underpowered for RepRap use, but so far they are working pretty well.  They can operate at full, 1/2, 1/4, or 1/8 step. I’ve been able to get the standard Gen3 firmware operating the at 1/8 step at pretty reasonable speeds (the fast traverse speed will definitely be lower than what I’m used to, though).   The smooth movement is very nice!

For a RepRap running on the Gen3 (Sanguino) firmware, the motor power requirements are primarily driven by the need to provide instantaneous large velocity changes.   So the second part of this effort will involve firmware changes to incorporate acceleration into the movement.  This should greatly reduce the stepper power requirements and make the lower power drivers a better fit.

However, the acceleration code is still a long way from being done — more about that later.

To make the EasyDriver boards easier to use, I’m building a board that can hold 4 of them.  The board just makes the wiring cleaner, and has dip switches that allow easy selection of the stepping modes.

One thing I didn’t consider when I started out designing my own repstrap is the adjustment process. It turns out that getting one of these printers tuned up and printing well is quite a tough project — and I’ve got a trashcan full of ABS to prove it!

Actually, now that I’ve done it once I think the process will be much easier in the future.

Today was the first day that I was able to make some acceptable looking prints.   Here’s a pic:

The prints are 20mm x 20mm x 10mm, with a 5mm round pocket.

A couple notes about the prints:

• I used the maximum extrusion flowrate (255), which required a feedrate of ~48mm/s.  At this speed, the printer is really flying!
• I was able to get great results without a raft by using double sided carpet tape on the build surface.  Not sure how it will work for larger prints, but the bottom surface finish is really nice.  I’ve got nothing against rafts — I was just looking for a way to speed up my test prints.
• Some of the initial problems I was having I tracked down to bugs in the Skeinforge code.  Enrique was awesome about responding to my bug reports, and quickly posting the fixed code — nice job Enrique!

The square rings are test prints I made to calibrate the single filament wall thickness.  For me, this was the key to getting the printer working well.   I can post more about the process if anyone is interested.

Here is a video of the printer in operation: