Sunday, 27 November 2016

Project: Proteus Delta part 5

Proteus Delta with current rod arms
     Last time, I'd just finished installing the steel rod arms, but I ran into a problem with 6 of them being too heavy for the motors to hold at the top unpowered. I replaced 3 of them with wooden shafted ones after some weighing and experimentation that showed the max unpowered holding weight of all 3 motors is around 900 grams or 300 grams per motor. 

Wooden rod arms being assembled
How to use 6inch/150mm calipers to measure long objects with some markings
     I'd mentioned measuring the rod arms in part 4, but didn't include details on how that was accomplished. I just wrapped some small pieces of electrical tape around the rod arms roughly 1/3 of the way along from each end as reference points, then measured the lengths of each section of rod, that puts my accuracy at +/- 0.03mm, since my calipers are accurate to +/- 0.01mm. The updated average length is 396.54 +/- 0.03mm, and that finishes the rod arms.
Left to right: Power supply bracket, 5x20mm 5A fast-blow fuse, power plug/switch
     After sorting out the rod arms, it was time to start on the electrical harness. I've already installed the motors and end-stops, so the power plug/switch unit is next. For wiring up one of these 'Power switch with fuse and socket' units I followed this guide by, it covers all of the details of setting up the mains wiring correctly. For the housing, I'm using a remix of this power inlet mount, with some added extra flanges to allow it to fit on the electrical conduit with the help of a shortened variant of the alternate conduit mounting brackets from the Emmett-Delta design. The printed parts are connected with 2 m3x50mm screws and a couple of m3 nylock nuts.

Power supply wired in and ready for securing
Power supply mounted and secured
Duet 0.8.5 mounting posts

     With the power supply fully installed, it's time to mount the Duet 0.8.5 onto the base and plug in the motors and end-stops. Since the Duet is designed to use function as a heat-sink for the stepper drivers, I designed some printable mounting posts to provide space for airflow under the board. Once mounted, it's mainly just a matter of plugging in the motors and end-stops to the relevant pins, which are helpfully marked on the underside of the board. It's worth noting that for micro-switch end-stops, the leads need to connect to the outer pins of the 3-pin connector, not the center and one side used on a RAMPS 1.4 derived board.

End-stop connector for Duet
Duet 0.8.5 mounted and partially wired
     That's it for now, my next step is to sort out the wiring pinout for the power supply's output, so I'll be breaking out the multimeter next time for exploring what pin gives what current level, along with mounting the cooling fans, but that's for next time.

End-stop wire routing at the top of the towers
End-stop wire routing at tower base, note the zip-tie retainer on the right
Proteus Delta almost ready for motion testing

Tuesday, 15 November 2016

Project: Proteus Delta Part 4

Rod arms and Effector installed
   Well, it's time to cover the last of the major mechanical assembly for the Proteus, building and installing the rod arms. Most deltas use carbon fiber tubing, Traxxas 5347 joints, and M4x20mm set screws for building the rod arms, but since carbon fiber tubing is a bit tricky to find locally, I'm using some 3/8" cold rolled steel that I got at the local hardware store instead. I've also designed some 3D printed end caps to allow using regular M4x20mm cap screws for mounting the traxxas joints onto the shafts.

Traxxas 5347 assembly tool and end cap cross section
     For assembling the Traxxas joints, I used the delightful tool pictured above, it's a fairly quick print, 30 minutes and it's ready for use after adding a M3x30mm or longer screw. As for the end caps, the STL is here, I'd recommend printing them on their side since the length of the lower point is fairly critical to getting the final arm length correct. After assembling the joints, the next step was tapping both the end caps and traxxas joints with a M4x0.7 tap to make installing the screws easier.

Threading the endcaps with a M4x0.7 tap

Completed end cap assembly
     After tapping, the actual assembly is fairly quick if you use a power drill to provide the rotational power, I've got it clamped in an old bench vise to make it easier to keep things aligned, but you can easily assemble things freehand with just a hand screwdriver. For the shafts, I used the same technique that I used for cutting the Mostly Printed CNC's tubing to length to cut 6 327mm sections and printed a jig for final assembly.

Steel shafts cut to length on jig for length checking
     Once the jig was printed and screwed down to an old 2x8, flattest surface I had on hand, it was simply a matter of mixing some 5-minute epoxy, applying some to the ends and pushing on the end cap assemblies, then placing it in the jig and letting things slide until it fits perfectly.

Fully assembled rod arms jigged and drying
    After everything was assembled and settled, I left the arms overnight to dry, and printed a customized version of this delta effector generator to use for the outer part of the effector platform. Measuring and averaging the final lengths of all 6 arms gives a center-to-center length of 396.34mm, one of the numbers needed for calibrating the Proteus when it's finished. Finally installing the arms on the rest of the frame was straight forward, just needed 12 m3x20mm screws.
Rod arms half installed
    Now all that's left is to redo the printbed support and install the electronics, but that's a topic for next time.

Monday, 7 November 2016

Project: Proteus Delta Part 3:

Proteus Delta half assembled
     It's been awhile since I last posted on this project, so here's how to assemble the slider/carriages and drive belts. Parts for this stage included 7 meters of GT2 belt, 9 Openbuilds solid V-wheels, and the 3 Nema 17 stepper drive motors.

Slider/carriage half assembled
     Once the printed parts are made, putting the sliders and carriages together is fairly straightforward, the only real tricks are that you'll need to print the front plates individually to avoid fractures and print the short version of the spacers, not the long ones which are on the left in the picture above, otherwise the belts won't line up properly. Otherwise, assembly is fairly simple, just insert some M3 nuts into the traps and screw the carriage to the slider, then insert and loosely thread a M3x20mm screw into the tensioning hole. Finally, use a pair of plyers and a 4mm hex key to put the spacers onto the M5x45mm socket bolts, followed by the solid v-wheels. The very last step is adding a nylock nut to the end of the bolt to hold everything, be careful not to overtighten it, the wheel should still be able to turn freely when everything is assembled.

Slider/carriage with short spacers installed
    As for installing the sliders onto the towers, it's simply a matter of pressing one side into the groove between the tubes, then twisting the carriage around the tower until all three wheels are aligned, followed by tightening the tension screw until the carriage has a firm grip.

How to properly assemble the idler mounts for installation
     Now that the carriages are installed, it's time to add the idlers and drive motors so the belts can be added. The Emmett delta design is a bit strange in this regard, since both the motors and idlers are adjustable to handle belt tensioning. For the idlers, there's a couple printed parts, along with a few M5 nuts and bolts to assemble everything. I'd recommend leaving things slightly loose until the belts are on, or you can tighten them down now and just use the motor mounts to adjust the belts.

Idler assembly fully installed
     Now that the idlers are installed, the next step is assembling and installing the motor brackets. I've used a slightly odd method for mounting the motors, a pair of M3x16mm screws with a couple of M3 nuts on the end as spacers, this is not something I'd recommend copying, it's just the result of my local hardware store not having M3x10mm screws in stock.

Motor assembly ready for installation
     For installing the motors, the sequence is bolt the mounting plate to the front of the motor, then install the drive pulley as shown. Make sure that one of the grub screws for the pulleys is aligned with the flatted side of the steppers shaft if you're using D-shaft steppers, this generally helps prevent the pulley from slipping during use.

Motor assembly installed and ready for addition of the drive belts
     Now, installing the mounting bolts for the motor brackets is a bit tricky, it's too tight in there for a crescent wrench or ratchet, so you'll need a 7mm metric wrench to tighten the bolts down there. I'd recommend leaving the upper bolts loose and tightening the lower ones to hold the motor at the top of it's range of motion, otherwise you will have difficulty tightening the drive belts to full tension. 

Using a rubber band to keep the sliders out of the way during motor installation.

I also found it helpful to get the sliders out of the way since they tend to rest directly above the motor mount and make access to the mounting bolts a bit difficult until the belts are installed. A simple rubber band provided a quick fix to this nuisance, although it's probably avoidable if you install the motors before the sliders.

Sliders with alternate carriages installed.
     I'd originally installed the Folger tech style carriages that are part of the printed parts listing, but they have a very strange way of locking the belts into place that just wasn't working for me, so I installed a set of these self locking carriages instead. After they where installed, it was fairly simple to loop the belts into place and then lower the motors to bring things up to tension. I've included a video below to show what the belts look and sound like once everything is tight.
Proteus Delta with motors and carriages/sliders installed

Drive belt installed on one of the carriages
     And that's it for installing the drive belts. Next time I'll cover how to build and install the rod arms and effector platform. I've also had the MPCNC involved in making a support for the build plate, I'll have more on that in a later post, but here's a teaser of the initial prototype.
Test fitting the prototype print bed support, still needs some work