Stepper Motor Testing

The racks, pinions, and power supply arrived yesterday and I setup a trial run to verify the motors would have enough speed/torque with the selected gear ratio. First, I bored a few thousands out of the pinions to allow a press-fit onto the stepper shafts. Next I pressed the pinions onto the stepper shafts; luckily the steppers have a hole in the back of the case that allowed me to support the other end of the motor shaft so that no force went through the motor bearings. I then verified the pinion/shaft run-out with a dial indicator; all except one were well under a thousandth. I was able to bend the one with a few thousandths run-out to match the rest; there was no way to protect the motor bearings during this process though so hopefully I didn’t cause any longevity problems.

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Once all the pinions were in place I cut the racks to final length and modified the Smoothieboard electronics and configuration files to accommodate a 2nd (and inverse rotation) motor on the X axis. I then wired it all up and began testing. It all seems to work great and I was getting what seems to be plenty to torque all the way up to 1200in/min. The rack also seemed to have very little backlash, even over a range of different engagement depths. I don’t have any good way to measure the torque, so I just pushed against the rack by hand with a force that I assume is far greater than the moving/cutting resistance. So it remains to be seen if 1200in/min will be the actual speed; I also verified there is even more torque at lower speed, so I can always slow it down if need-be. Speed will probably be limited more by the spindle/tooling/material anyways.

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CNC Machine Planning Pt2

Since the last update I’ve completed the machine design and ordered a majority of the metal and mechanical parts. Some of the components’ 3D models (smoothieboard, power supply) were available online, which saved some time, but I had to model the majority from scratch. The design uses all the actual part dimensions to ensure there won’t be any part interference and that the range-of-motion will be OK. Getting the dimensions right so that there is no interference while also not having any wasted travel is actually much harder than it looks and a lot of time was spent perfecting this. As a result, the clearances are fairly tight, but this machine is meant to be as compact as possible so this is intentional. The overall usable table size worked out to be 48″x18″, with a machine footprint of 52″x24″. Some design highlights:

  • Strategically placed bolted connections to allow for adjustment of squareness and rack/pinion mesh.
  • Minimize weldment complexity and dimension criticality. It will still require a lot of attention during fabrication, easily the most dimension-critical thing I’ve fabricated.
  • X rails flush with the back of the table to allow for future expansion.
  • Parts will be held to the table with temporary clips screwed into a sacrificial fiberboard table;when the fiberboard becomes too full of screw holes it will be replaceable. The spindle centerline will be able to reach every part of the table to allow it to be surfaced flat.
  • The electrical enclosure occupies the rear area that is unreachable by the spindle. Unfortunately the height of the power supplies makes the enclosure higher than the table surface, so if the machine needs to be temporarily expanded I’ll have to build up the table surface over the enclosure and sacrifice some Z travel. This won’t be a big problem though since the type of things I’d do in ‘expanded table mode’ wouldn’t require much Z anyways. (Making the base taller would have fixed this, but since it’s going to live on the workbench all the time I’d rather keep the base as flat as possible)
  • Z axis uses a standard extrusion; this will give the most flexibility with mounting different tools
  • I included a provision for a pneumatic cylinder in the design to counter-balance the Z axis. This will allow the Z axis weight to be precisely offset by adjusting air pressure. I’ll wait and see how it works though before deciding to either add this, a gas strut of the same size, or nothing.

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CNC Machine Planning

I’ve had on my list for a long while now that when the bus was ‘done’ I’d get back into hobby electronics/robotics. I can’t think of a better way to kick this off than by creating a CNC machine; it’s a fun project on it’s own but will also make many of the miscellaneous fabrication tasks for projects of all categories (hobby/bus/home) easier, faster, and of much higher quality.

Design Requirements:
#1 – More or less fit within a 4ft wide by 2ft deep x 20in tall area; allowing it to live full-time on the garage workbench without being in the way. Also attempt to minimize deck height and park moving axes flat against the back wall for the same reason.
#2 – Be able to cut 4×8 material if needed. (Does not conflict with #1, design just needs to allow for future temporary extension & relocation)
#3 – Initial build will be a router, but the design needs to be flexible enough to support future tool types (3D printer extruder, drag knife, low power laser, etc)
#4 – Accurate enough for #3; maybe +/- 10 thou?
#5 – Rigid enough for #’s 3 & 4, but not to the extent that it becomes an immovable object like a Bridgeport.
#6 – Faster than a snails pace but speed isn’t all that important, not a production line machine.
#7 – Reduce cost to the lowest possible while maintaining good quality. Utilize all welding/machining/painting skills learned in other projects to build mostly from raw materials to save cost. Utilize “off-the-shelf” components in creative ways.

As far as machine configuration goes, the choices are: Delta, Cartesian, or SCARA. I made a quick sketch of the simplest forms of each below. Although the delta configuration is currently very popular in the 3D printing world, I immediately ruled it out as being incompatible with my size and tooling requirements. A SCARA configuration was very tempting as it could fold itself up into one corner when not in use. I had to rule it out though because the geometry is just too weird for my liking, all limits and resolution are polar; in other words the resolution changes with distance away from the base and the machine limits are circular instead of rectangular. This left me with the tried-and-true Cartesian configuration.

Robot Types

I’ll base the controls on the open source SmoothieBoard project, which itself is based on the open source GRBL (pronounced ‘Gerbil’) project. I’m confident I could have designed/built/programmed this all myself from scratch and it would have worked, but wouldn’t be quite as good as a well developed community-based project and I’d rather just focus on getting the overall project up and running. The SmoothieBoard will directly drive at least three 2A stepper motors (X/Y/Z), and perhaps also a 4th motor working in parallel with one of the others depending on the mechanical design.

I’m dusting off my old student copy of Autodesk Inventor and beginning on the mechanical design now. It’s still very much in the initial stages and I’d rather build it digitally 20x and physically once, so it may take a while to perfect to the point of beginning construction. Currently some of the brainstorming questions are:

Machine frame?
Black Pipe: +Cheapest Option, +Cast Iron good at damping, -Bad Tolerances, -Weldability Questionable
Mild Steel Tubing: -/+ Good middle ground between other two options?
Aluminum Extrusion: +Quick assembly, +Good Tolerances, -Expensive, -“too easy”/looks-like-an-erector-set
Drivetrain?
Rack & Pinion: +McMaster has decent looking sets for reasonable cost, +Easy to extend, -Backlash
Ballscrew: +Low Backlash, -Even the ‘cheap’ ones are expensive, -Impossible to extend temporarily
Belt or Chain: +Simple to experiment with ratios, -Difficult to extend temporarily, -Stretch/Backlash
Linear Guides?
Homemade: +Design Flexibility, -Requires complex fabrication of slides w/ small bearings
Bought: +Known-good performance, -Expensive, -Limited length/size options
Is there a 3rd option? Possible to buy slides to use with some nominal tubing size?

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Adding Auto-Refill to Keurig

It’s not that manually refilling a Keurig tank is hard, it’s just unnecessary. Commercial Keurigs (and some of the high-end home versions) are built with this in mind and can be directly plumbed for water. Our Keurig, however, is a ‘normal’ home machine without provisions for direct plumbing; so some creativity was involved in adapting it for this feature. Altogether this was a fairly simple 3-step process:

#1 – Make bracket from scrap piece of PVC pipe.

#2 – Install miniature float valve ($3 w/ free shipping) and bracket into tank.

#3 – Plumb float valve to existing water filter under sink.

All plumbing is nicely concealed behind the microwave/cabinets, so the only evidence of anything different is the float visible in the tank. Before anyone freaks out about the evil toxic plastic floating in the water, I should point out that the tank itself is plastic anyways, as is much of the tubing that supplies water to the faucet when filling the old-fashioned way. Total project cost was well under $10.

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Winter Update

Aviation: Winter is here and with it has come lots of overcast weather that’s no good for flight training, slowing progress quite a bit. In total I’ve now soloed 6-8 times and have started working on cross-country training. Cross-country flying adds many new elements: flight planning, talking to Air Traffic Control, radio navigation, visual navigation by waypoints, etc. All this has to be done while still flying the plane, so it’s definitely a challenge. Currently targeting to have my FAA checkride sometime before April.

Home/DIY: A number of small update/repair projects completed: Added a range hood, re-plumbed the fridge water supply for better flow, repainted the kitchen cabinets. I also have one big project underway with insulating/encapsulating/cleaning the crawlspace; this project started off with a bang and I’m probably 1/3 done already, but I’ve let it lose momentum; as long as it’s done by spring.

Bus: Winter also puts a damper on bus driving since I don’t have the heat connected yet. On the last drive before the temperature dropped I had a big loss in power every few minutes and had to pull over and idle before power came back. I haven’t looked into it yet but this seems consistent with a clogged fuel filter; I was expecting the first filter to go quickly since it’s filtering out all the rust/varnish/trash from the fuel tank that sat for 30 years. I probably could swap the filter and have it going again but I think this is a good opportunity to now pull the engine/trans again and go through it with a fine-tooth comb with the goal of getting it smoother/quieter/stronger to enable longer trips. No immediate plans to do this, probably when the weather warms up.

Tech Projects: I just ordered a float valve to automate refilling the Keurig, I’ll post pictures of how that goes. Also I’m getting interested in making a small CNC machine; I’ve had this on my long-term to do list for a while but recently component prices have dropped substantially so I’ve started the planning process.

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First Solo Flight!

Originally this weekend was to be my first solo flight. Sunday I showed the instructor 3 takeoffs, 3 landings, and got signed off to fly solo. Just as we taxied back to the ramp to let the instructor out though, the weather report changed and exceeded the limits that I’m signed off for (12knots total wind, up to 5knots crosswind component). Because of this, we delayed the actual solo until this evening after work.

So today I was back at the field and everything went well. There’s a tradition in aviation that when a student first solos the instructor cuts off the student’s shirt tail; supposedly this dates back to the early days of biplane aviation when the instructor sat behind the student and pulled on the student’s shirt tail to get attention. When I taxied back to the ramp my instructor was ready with scissors…

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I’m told it goes relatively quickly from here but I know there’s a lot left to learn; I’ll now do some practicing on my own and then we’ll get into cross-country flying and procedures for ATC communication.

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Blimp Encounter

Today I was back at the airport after nearly a month away from flying due to weather/maintenance/availability/etc. After takeoff I did some basic instrument flying. Instrument rating is a separate rating on top of the private pilot’s certificate. I’m not working on an instrument rating, but the basic instrument skills are taught/practiced anyways to have some level of familiarity in case I ever accidentally encounter instrument conditions. As I was doing the preflight, the MetLife blimp arrived at the field and we got to watch it land (if this is even the right word; it just got close to the ground and then a dozen guys ran out and grabbed the ropes). It was moored directly adjacent to the runway, so I got a few close-up glances while I was busy taking off and landing. After landing we heard them announce (their callsign was “Snoopy2”) a 5min warning for departure and by the time we got back to the ramp it was taking off.

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Using a Real Aviation Headset with a PC Simulator

In parallel with real-world flight training I’ve begun to use a PC flight simulator more seriously. This reinforces what’s learned in the real plane and also allows me to practice flights ahead of time. The simulator is only vaguely analogous to real flying though, so the more I can do to make it realistic the better. One realism point would be to use the real aviation headset, but the headset does not directly plug into the PC. After a good bit of research cross-referencing part numbers and checking schematics, I came to two critical conclusions:

#1 – Standard 1/4″ mono audio dimensions are the same as general aviation headset plug dimensions. (The speaker plug, not the microphone plug)

#2 – The sound card output levels are compatible with the headset’s required input level. (not so low that they’d be inaudible, and not so high that they’d blow out the speakers on even the lowest setting)

Once those realizations were made it was easy enough to make an adapter cable from a scrap audio cord and a $2 1/4″ mono jack. There are ready-made adapters online, but these go for far more then even the standard 5X markup for anything with ‘aviation’ in the description; so it was worth the effort to spend a few minutes and build myself. The microphone connector is more special-purpose and would require finding the special jack and likely some circuitry to make the levels work for the PC mic input, I don’t do anything in the simulator that requires the microphone though, so that connection just stays unplugged.

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Golf Coolant Leak Repair

A few weeks ago the Golf gave a low coolant warning and, not seeing any immediate signs of a leak, I topped if off. This week, I noticed a few pink drips in the garage. This is actually fortunate because it meant there was an external leak of some kind rather than something more serious like an EGR cooler or head gasket leak. Since the puddles were rapidly increasing in size I investigated the source of the leak tonight. Unfortunately it wasn’t anything as easy as a bad hose, clamp, or o-ring; I could see coolant dripping from the radiator. The next step, as it is with most modern VW repairs, was to disassemble the entire car. Although it looks intense, cleaning up the garage prior to starting this project took about as long as actually accessing the radiator.

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From searches online it appears this is a somewhat common problem; the fan support vibrates against the thin aluminum radiator tubes until a hole is worn through. During reassembly I’ll add some rubber cushioning in this area to prevent recurrence. A replacement is available locally and I’ll pick it up after work tomorrow; I should be able to have everything back together tomorrow night, though I may let the project stretch into the weekend to thoroughly clean/detail the front bumper while I have everything apart.

Update: Finished this Friday night, relatively easy, no more leak.

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Carpentry & Aviation

Today (I have a few days off of work), after a few months of studying in my spare time, I finally took the controls of a Cessna 172 for about an hour. With direction from the instructor I taxied, took-off, climbed to 2000ft, and then maneuvered around and even did part of the landing approach; though the instructor did the landing itself. I’ve got a long way to go but over then next year or so I’ll be flying somewhat frequently to make progress towards a private pilot certificate. Anytime a new skill can be learned (i.e. welding/painting/etc from the bus project) I find that it can be beneficial in unexpected ways, even for seemingly unrelated tasks/problems. So this is about having another tool in the mental toolbox, and I’ve always been interested in aviation anyways…

After arriving back from the flight I starting working on installing crown molding in the downstairs bathroom. For some reason this was the only room in the house that didn’t have it and I always thought it looked odd. In the past, I’ve just propped the molding up at the correct angle and hand sawed at 45degrees in a miter box. Due to the number of joints though I decided to get fancy and make the cuts on the tablesaw. This presents a problem since, when the molding is flat on the table, the angles are in two different directions: a compound angle in which the blade must be tilted and the material angled against the push fence. Luckily I’m not the first person to ever do this so I found tables online of compound angles for a given wall angle (90deg nearly always) and a given trim angle (the angle the trim sits against the wall). There was some scrap made while learning what orientation to use for a given angle; 4 of the 8 combinations don’t make anything useful (i.e. inside right/outside left/etc.) More than a few times during this process I thought back to how much easier flying the plane was (or at least seemed) earlier in the day.

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