Tuesday, January 28, 2014

Delta Bot #4: Heated Build Platform + Initial Electronics

Next up on the delta robot 3D printer- cutting out the plywood for the build platform, and initial electronics installation.

I picked up a 2'x4' 1/2" plywood handipanel from home depot for the build platform. I decided to cut out a 14" circular platform. I used a scrap piece of wood with two holes drilled in it to trace out a circle- pinning the center with a drill bit.

Tracing the outline
Circular plywood platform cut out- trial fitting
I used 4-40 blind nuts set into the bottom of the platform to fasten the heated bed in place

4-40 Blind nut pulled into place
Under the heated bed I placed two layers of cork tile- totaling about 3/8" in height. The cork will insulate the bottom of the heated bed and hopefully help it heat up faster and maintain a constant temp during print jobs. The heated bed is held in place with 4x 1" 4-40" SHCS, with a printed spacer and a 4-40 washer between the bottom of the bed and the top of the plywood platform.

Everything bolted into place
Next step was to wire the endstop switches. I had a big spool of CAT 5e cable in the garage- perfect. It has enough individual wire strands for all three endstops and another two left over.

Endstop with wire soldered and heat shrink in place

I drew up and printed some wire clips that snap into the Makerslide aluminum extrusion. I'll upload the models to Thingiverse as soon as the site is back up. 
Makerslide wire clip

UPS brought some goodies this week- a RAMPS FD printer driver board. I'm hoping to plug it into a UDOO dual core board, and use the assembly as an all-in-one printer controller & driver. 

RAMPS FD out of the anti-static bag. I'm digging the side connectors for the stepper motors. 

Dual core UDOO

All plugged together and ready to roll
Next up, actually getting something to move...

Wednesday, January 22, 2014

Delta Bot Build Part #3: Effector Rods & Hot-End platform

Finally, more progress on the 3D printer! With the frame designed, printed, and bolted together, it was time to move on to the moving parts. All part files are up on Thingiverse.

I ended up going through several revisions of both the hot-end platform, and the carriage mounts for the rod-ends. The versions shown in the pictures are not necessarily the latest version. I've kept the Thingiverse file list updated with the latest files.

Hot-End Platform on the Left, Rod Sleeves on the right.
I chose to use 8.5mm OD x 7.25mm ID carbon rods for the effector rods. I sourced them from Hub Hobby. The smaller diameter rods just didn't seem to be stiff enough. Another nice thing about this particular diameter is the Traxxas 5525 rod ends slip right into the ID of the tube. One thing I did notice was the rods seemed to split easily at the ends. I thought a simple solution was to print some thin-walled sleeves to epoxy over the ends to reinforce the rod-ends. 

My original, wimpy carriage rod ends
My first go at the design for rod-end carriage mounts looked fine on Solidworks, but after I printed them I thought they looked weak and flexy. You'll see later, beefier versions printed in yellow in the photographs below.

Fixture for making the effector rods
One key dimension to get right is the rod ends- the exact length isn't extremely important, but the consistency of length is. If possible each rod's eyelet to eyelet distance should be as close as possible to the same length as the rest. I accomplished this by making a simple fixture. My intended rod length was 250mm, so I drilled some holes in some plywood scrap 250mm apart, and pressed in a pair of 3mm SHCSs.

To make the effector rods, I first cut the rods to length (230mm) using an X-acto razor saw. Then, I epoxied the printed rod sleeves onto each end of the six rods.  When I epoxied the Traxxas 5525 rod ends into the ends of the carbon rod, I did it one rod at a time, and after applying the epoxy I slid the tie-rod ends over the screws in the fixture. So, when the epoxy finished curing, each rod was almost exactly the same length.

Finished Effector Tie-Rods, lightweight and strong as heck
The next thing to do was to bolt everything together and see how much backlash / slop there was in the system. Everything fit well- after revising the design several times to fix some perceived strength concerns, and to adjust fits, types of screws used, and method of clamping the rod-ends into place. One disturbing thing I found out was that the parts in a bag of Traxxas 5525 rod ends not all ends were the same- some had slightly different fittings on the end. I ended up having to shim the parts using 3mm washers to maintain a consistent spacing.

Note the yellow parts in the pictures, different than the original black shown above.

Assembled frame & platform. I really need a better photo backdrop!

Close-up of the frame and effector rods

Again, the carriage mounts and platform shown in the photos are not the latest and greatest, I did more revisions after they were taken.
Unfortunately the assembly isn't nearly as slop / backlash free as I'd like. I can grab the platform and wiggle it back and forth about 1mm. Much too much slop to produce a quality print. The slop all seems to be coming from some side-to-side play within the Traxxas tie rod-ends. A friend suggested going to magnetic arms- and I ordered some spherical 10mm magnets off of e-bay to give it a try. The Cherry Pi Delta 3D printer on thingiverse has a really cool implementation that I'll probably modify and try out.

Another option would be to use a pair of springs (or rubber bands) on the ends of each arm to pre-load the arms and eliminate the slop. I might try that short term as it's quick and easy.

Next up was to design and print endstop switch and adjustment screw mounts. At least initially I'll use the trusty RadioShack sub-miniature lever switch.

Mounts seen in yellow. The carriage is all the way up, with the M5 screw triggering the endstop switch
 I think the next step will be to build the platform for the heated bed, and start wiring it up!

Friday, January 3, 2014

Delta Bot Build: Part #2 Belt Tensioners

After initially assembling the frame and trying my first belt tensioner design, I realized that putting the belt tensioners on the moving carriages just clutters up the design and adds additional mass to moving parts. I decided to move the tensioners to the top of the towers instead.

After searching through thingiverse for examples of rostock / delta bot 3D printer belt tensioners, I initially considered mounting the belt idler wheels on an arm that could rotate and thus tension the belt, but as the idler would move in an arc, the belt would possibly rub against the side of the idler mount. Instead of trying to concoct a four-bar linkage that would keep the idler moving in a straight line up and down, I went with a much simpler concept. The idler will be mounted on a plaftform that is moved up and down with three screws, thus tensioning the belt.

All parts are printed with a 0.5mm nozzle, 0.5mm layer height, and 50% fill density. I chose the big nozzle and layer height to maximize part strength. I think fewer layers = better strength, less chance of delamination.

Idler carriage printed and assembled

bottom view- note M5 captive nuts pressed into place

New upper corner bracket installed and belt fed through, ready for idler carriage

idler carriage in place and ready for tensioning

Successfully tensioned!
It seems like this concept works- so I just started printing another set. Hopefully I'll have enough red to finish, this spool is just about finished.

Wednesday, January 1, 2014

Improved filament guide, part 2

I'm a little obsessed with making the filament feed system on my MendelMax as perfect as possible. I've had lots of problems with tangled filaments in the past, and it seems as though a lower-friction feed system should also improve part quality.  The last round of improvements helped, but there were still a couple places where the filament was exposed to sliding friction. I have a bunch of big parts I'm printing for the new delta robot build, and I want to eliminate problems before I waste a lot of filament printing junk.

So, I decided to go crazy with 608 sealed bearings- they are cheap, and I have a bunch left over from the original MendelMax build. I replaced the right-hand side guide post on the upper guide with a bearing, and created a new lower guide with two bearings.

New upper filament guide

New lower filament guide
So far the new guides seem to work great. No tangles yet, and I'm printing a new set of parts for the delta robot build right now.

I posted the files on Thingiverse: http://www.thingiverse.com/thing:199104