MendelMax 1.5 Build Log: Part 1

As a part of my job, I've used many "3D printing" services over the years to construct medical device prototypes- SLA, Polyjet, rapid CNC, etc. I've always thought they would be far too expensive to use for home projects and hobbies. A few weeks ago I was doing some research on in-office prototyping equipment and discovered that hobbyist-level equipment had come way down in price, and there were tons of options for cobbling one together using open-source software and hardware.

Having the ability to make just about any plastic part in your house sounded great. Replacement parts for anything in the home, broken or lost parts to kid's toys, designing new bike accessories, model airplane parts, whatever. Even doing some "lost-wax" style aluminum casting would be fun to do. Plus, there is an enormous amount of free 3D models available online for download and printing at Thingiverse among other places. It might even be useful for manufacturing items to sell on ebay.

RepRap is one of the main open source systems out there, and after doing some research, I decided to build a variant called MendelMax 1.5. The idea behind RepRap is that each completed printer can replicate itself by printing components for another printer. MendelMax was attractive because it used industrial aluminum extrusions to build the frame, there is a local industrial salvage company called D&S machined products that has a large inventory for very reasonable prices.

Mendel Max Illustration from Thingiverse

Video of someone's Mendel Max 1.5 in action:

Since the MendelMax is just one of the million flavors of RepRap out in the wild, there is some documentation available:
MendelMax 1.5 on Thingiverse
Great Build Log for 1.5
Trinity Lab's outstanding build manual

But, as I found out, a MendelMax 1.5 isn't a uniform species. Everyone has their own tweaks. So, when you order a kit of printed parts from someone, pay very careful attention to exact what hardware you need- it isn't the same from kit to kit. I'm sure it'll change eventually, but right now building a 3D printer is definitely for someone who wants to get their hands dirty and dive into all the details- it's not a plug and play deal.

Since I don't know anyone with a printer, I had to buy the parts. I ordered my kit from Lulzbot.com. They have a polished website, and their customer service was quick to answer questions via e-mail before the purchase. However, their site is a little confusing with many broken links and not a clear BOM to tell you what you need for the 1.5 build. In particular, the kit doesn't include the X-axis parts, and the components to finish the Y axis. If I were to build another with purchased components, I'd probably buy a more complete printed part kit from another source.

I ordered the hardware from McMastercarr.com- lots and lots of metric SHCS, drill rod for ways, etc. Once the build is complete I'll post a complete BOM with sources. I haven't yet decided on which electronic package to use and where to source it.

On to the hardware build:

I purchased some used Bosch 20mm extrusions from D&S. They were in great shape, just a few un-needed holes here and there. I was able to cut them to length using my power miter saw with a standard fine tooth carbide blade. I did clamp the extrusion to the saw and made the cut very slowly. The cut quality turned out almost perfect- I didn't have to do any cleanup filing at all. One of the biggest problems was just finding a metric tape measure- all the majors didn't carry one- Menards, Home Depot, Lowes all lacked a metric tape. Then I remembered that QBP gave away a free tape measure during one of their open houses years ago. I dug it out of my bike toolbox and it worked great.

Cut Quality Illustration

300mm and 420mm Extrusions for printer base

I used the Trinity Labs manual as a guide for assembling the frame.  One big difference between their build and the Lulzbot 1.5 design is that Trinity 1.5 uses a linear slide for the Y axis, and the Lulzbot uses two 8mm diameter precision drill rods for the ways. I had to dis-assemble the base so I could insert some additional T-slot nuts to accomidate the Y-axis rod mounts.

Note that all of the black plastic parts seen in the photos are 3D printed ABS parts purchased from Lulzbot.com.

Assembled MendelMax 1.5 base with Rod mounts in place

Y Axis Rod Mount detail

Rod Clamps in place

 Since the clamps (like all the plastic parts) were 3D printed, curved surfaces are stepped and are not totally precise. I assembled the rod clamps then drilled them out to clean up the surfaces so they would properly clamp on the 8mm rod.

Cleaning up Clamp to fit 8mm Drill Rod (don't worry, the skewed angle of the drill is only because I was also holding a camera, it was square when I actually drilled the hole)

Test Fit of the 8mm Drill Rod

Cutting the drill rod to length using a hack-saw, vise, and plenty of oil

The Lulzbot MendelMax 1.5 kit didn't include the Y-axis busing holders, so at least for now I'll have to build the frame without the build platform in place.

Ways in place, with 8mm SDP bushings mounted

 The build platform moves front to back on the Y-axis slides. It's driven by a stepper motor through a GT2 timing belt. The motor mounts on the "back" of the device base, and the belt tensioner / idler mounts on the "front" of the base. I don't yet have the bearings for the idler. Those will be added later.

Y-Axis Idler / Tensioner mounted

The screw on the top presses against the base extrusions to add tension to the belt

Next step after the base was built was to add the upper platform. Yet another Lulzbot annoyance- I found out the they had included 4x of the Lower Vertex (left) mounts, instead of 2x Left and 2x Right. I assembled the platform anyway just so I could get as much assembly done as possible. The Lower Vertex mounts connect the diagonal beams with the base platform. You can see the incorrect part being used on the lower right hand side of the photo- with the "left" component being using on the "right" side. 

UPDATE: Lightning fast customer support from Lulzbot- they said they'd ship out the replacement parts today as well as fix the broken links on their 1.5 kit web page.

Assembled Frame, back view

Assembled Frame, Front View

I did order the X-axis set from Lulzbot. I was only able to press the bushings into the X-slide before I ran out of fasteners and hardware. I didn't clean out the holes quite well enough- in the process of pressing in the bushings I managed to crack one of the bushing sockets. I think I'll be able to epoxy it together. Once the printer is up and running I can simply print a new replacement part.

Pressing 8mm Bushings into X-Axis Slide Using Vise

I ordered the ACME lead screws (for the Z-axis) and many fasteners from McMaster. I also need the bushing holders for the Y and Z axis before I can continue.

Real Snow!

Can't Wait for Snow

Until then, the 9:zero:7 has to be content with bushwacking over frozen sand.

This morning I decided to look for some new dirt on the way to work. There are numerous small trails around Parkers Lake. I played around there for a bit, then took the beach back to the Luce Line. 

More Q450 FPV Video

I'm still not flying through the FPV downlink, but practice makes perfect....

Flight #1


Don't worry- the only damage was a broken prop and re-breaking one of the landing gear legs


Flight #2



A little smoother... The 5.8 Ghz transmitter doesn't do too bad, even when trying to push a signal all the way through the house. I'll do a longer range test one of these days in an open field after I have the wide angle lens and some more quad flight confidence under my belt.

Initial Q450 Quad flight while recording FPV video

I received the replacement component video recorder yesterday, and was able to get the video input/output cableing sorted out. One thing I quickly learned was that 4 pole 3.5mm plugs (looks like headphone plugs but with one additional pole) do not have a standard pin-out. I'm going to have to manually take apart the cables and re-wire several of the poles to permanently fix my cable setup, but until then I'm just inserting the plugs partially into the sockets on the recorder. It's very hack but it's working. 

The initial flight was a line of site (LOS) flight indoors. Moral of the story- don't be messing with your auto-level settings while at the same time trying to pilot a quad around near the ceiling.

The crash looked bad, but the only damage was one broken landing gear leg. A little CA + UV cure glue and it's good as new. Maybe better, as now it has a nice fillet at the joint.

5VDC Power Supply for video recorder

The upcoming video recorder needs 5V DC. Since I want the ground station to run off of one 11.1V battery, some sort of DC to DC power supply is needed. I didn't want to do anything fancy- so I did some web searches and decided to go with a simple 7805 voltage regulator circuit. It isn't particularly efficient, but it's simple, cheap, and I had the parts available.

Basic circuit diagram (7805 is center component)

Circuit Breadboarded. I added a LED (with current limiting resistor) to show on/off status

Circuit moved to permanent breadboard

Soldered Breadboard (extra length of leads were trimmed after testing)

Finished, with heatsink on 7805

9:zero:7 First Ride!

After much deliberation, I picked up a new mountain bike last week- a 9:zero:7 fatbike.

I took Friday afternoon off to get in some dirt rides before the snow flies. I decided to hit some trails I'd probably be riding after we see some snow- the Minnesota River Bottoms and Lake Rebecca Park Reserve. The River Bottoms were a blast from the past- I haven't been down there in over 10 years. It was surprisingly warm- I ended up riding in shorts and a long sleeve jersey.

The new bike was great- handled really well, unlimited cornering traction, and a nice smooth ride. It also was great on the loose sandy sections- just floated right over them and tracked straight and true. Overall I'm very happy with it so far. I hope to have lots of great adventures with this bike. I still have to get the ergos dialed in. I'm going to exchange the post for a setback Thomson- I currently have the seat jammed as far back as it can go. They Thomson's 440mm length will also help- the stock seatpost is 1/4" over the maximum extension markings.

Lake Rebecca was surprisingly not bad. I've never ridden there just because I've never heard anything good about it. While it is totally non-technical, there is lots of climbing. If anything it reminded me of Lebanon Hills before MORC came in- lots of steep up and downs, straight up and down the side of the hills. There is lots of space and vertical relief at Lake Rebecca, so if Three Rivers Park District ever decides to improve the riding there, they could really put in a sweet trail.











 

FPV Goes Live

"First Light" today on the Q450 quadcopter! I don't have any video available yet because I don't yet have the video recorder. The final steps left before I could fire it up for the first time was simply to mount the camera and video TX on the quad.

Camera Mount

After using a plastic electrical box cover to make the KK2.0 Flight Controller mount, I thought I could find something in the Menards electrical aisle that would work well for a camera mount. Low and behold, a low voltage box looked like it would work great. One low voltage box will make two camera mounts- maybe one FPV camera and one GoPro?

Low voltage box with the trim lines marked

Test Fitting the camera

Test fitting camera after trimming box

Camera Mounted- 2-56 x 1/2" machine screws, lock nuts, and rubber grommets between camera and mount. Hopefully the grommets will act like enough of a shock mount to prevent vibration from shaking camera too much.

Note slot cut in base using dremmel cut-off wheel

Bolted to Hobbyking Q450 quadcopter frame

Video Transmitter (TX) mounted to the "roll cage" using velcro tape and a zip tie

Flight!
So, the big question- how does it work? No video or photos yet... The video quality looks pretty good, but when the motors throttle up there is a fair amount of vibration visible. I'll have to use thicker / softer grommets to isolate the camera better. The camera body might also be touching the orange plastic of the mount- I'll have to grind some material off of the mount to eliminate any possible contact. Other than that, looks great. It was already dark outside so I wasn't able to try any test flights of any distance.

Changing out the old Canon point-and-shoot for the FPV camera and Video TX didn't seem to affect the balance of the quad- no trim adjustments necessary. Adding a GoPro or similar might change the CG more.

I did adjust the camera mount slightly down so it wasn't looking through the rotors. It was very easy to do- just use a small torch to carefully heat the bottom edge of the camera mount, and when the plastic starts getting soft just bend to the desired angle. Not bad for a very cheap DIY FPV camera mount.

FPV- A couple steps closer

So far it seems like getting an FPV quad up in the air consists mostly of soldering a lot of cables together.



Ground Station Progress

Cut Video RX power cable in half, then added an EC3 connector

DC Power plugs for the portable DVD player

I was able to find a great deal on a portable DVD player on Craigslist. This seems to be a great option for a ground station monitor- just make sure it has a video input. The Magnavox I found for $20 has both video input, built-in batteries, and runs off of 9V DC. I removed the battery which dropped the current consumption considerably. Also, so far, it seems like it runs just fine off of a 11.1v 3s LIPO battery. The only annoying thing is that each time you turn on the DVD player, you must manually switch it to video in. Perhaps some surgery on the unit will fix that.....

Another note is that the video RX and DVD player both use 3.5mm 4-pole cables- which are very, very hard to find anywhere locally. These cables look just like headphone cables, but with an additional pole. MCM Electronics has a bunch of very reasonably priced cable options. 

I have a composite video to SD card video recorder on order, also from MCM. This will be very nice for post flight (crash) analysis.

Composite Video to SD Card Converter with AudioMCM Part #: 58-16090  |  Vupoint Solutions Part #: DVC-ST100-VP-BX2

Magnavox portable DVD player (from Craigslist, $20) connected to Video RX (upper center) and power panel (left). See the live video feed on the monitor!

 

Back of power panel. Fuse- to prevent big problems in case of a short. Lighted power switch, and two barrier strips. Below are the power leads for the DVD player and the video RX. There is room on the panel to also add power leads for the upcoming video recorder.

Nice bonus- Video RX + DVD player on only pulls 0.8 amps. (with DVD battery removed) It'll run for plenty of time on standard size 3s LIPOs.

Where to mount the ground station? How about this sweet (and cheap) soft sided suitcase from IKEA!

A couple rivets and velcro should do nicely to hold all the ground station components in place.

Quad-Copter FPV Progress

Camera with wiring harness, before modifications

Video TX, before modification.

Connecting the camera to the video TX couldn't be easier. Connect the camera power leads (red and black) to the power output on the video TX- red and black part of the large group of multi-color wires. Then connect the composite video leads- yellow on the video TX cable bundle, and white on the camera's cable. That's all there is to it. The camera now has power, and the video TX now has a signal. I used some male and female break-away headers from another project to make home-made plugs.

Home-Made connectors using "break away headers" - these were secured together using electrical tape once installed on the aircraft

I'm still trying to get Hobbyking to send me the OSD module that was missing from OSD package. Whenever that shows up (hopefully this year!) it'll also get wired in to the composite video lead. The OSD will provide some very valuable data- namely flight pack voltage and a return to home vector. Both of these pieces of information  will be overlaid on the video that is broadcast to the ground station. Until that is in place I'll have to depend on the low voltage alarm that is currently mounted on the quad. 

Next step, provide power for the video TX. Since this is going to be a very basic FPV setup with limited range and capabilities, I chose to save cost and weight and powered the video system from the main flight battery. A more robust route would be to use an additional battery pack. This particular camera and video TX like 12v DC, so the 11.1v 3s flight pack works just fine.

Added additional JST connector to Quad power distribution board to power the camera and video TX

Camera and Video TX, powered up by the Quad's onboard power

Next steps- build a camera mount. Ideally it'll accommodate the low-resolution FPV camera as well as a second HD camera, eventually a GoPro or similar.