Room equalization

This is a topic that I’m still fairly shaky on, so anybody out there reading this as a possible reference should probably take this all with a grain of salt. After building the LX521 speakers I could tell that they weren’t delivering precisely the sound that I know that they’re capable of when they’re set up correctly. As you’ve probably seen in photos, Siegfried Linkwitz’s home does not have any visible acoustic treatment, just some normal ‘stuff’ around the room. Furniture, a nice rug on the ground, nothing like walls full of acoustic foam or avant garde looking diffusers. It’s just a regular room, and most people who build his designs agree that you don’t to do anything special to get the good sound.

Before we go too much farther, I should say that there are two different things that I’ve noticed about the sound in my system that differ from what I heard when I auditioned the original. First, I hear a bit more of the room in the bass response than expected. Things boom/echo just a bit, and its’ the difference between a natural sounding reproduction of a sound that can truly fool you, and the sound of a speaker in a room. We’re not *quite* there yet, though it’s miles better than what I had before. The second part is that there’s a bit of imprecision in the imaging. In the demo I could very plainly localize sounds in space, like I could hear a xylophone player moving up and down the keys and tell the left/right position of each key. That might sound like a wild claim, but that’s what I heard and what convinced me that this thing was worth building. Having my TV between the speakers may be hurting the sound a bit, but I think there’s more that needs to change than just that.

I’m setting out to learn how to improve the sound of the speakers in my room, and I want to be able to do this well enough that when we eventually move I’ll be able to repeat the process with a reasonable certainty that I’ll be able to make the stereo sound good there too. I’m using a program called Room EQ Wizard (REW) to perform measurements. I use a Behringer ECM8000 room measurement microphone that I’ve had for years, a small powered mixer, and my computer sound card to capture the sound. Based on the reputation of the microphone and a loop-back measurement that I did with the rest of the signal chain, I think I have a fairly accurate measurement system…. if I can figure out how to use it right.


For my first measurement I put the microphone on a tripod positioned at the spot where my head would usually be, and ran a test sweep from 20hz to 400hz. I did a few more, but for the purposes of room equalization I thought that I was interested in things below 200hz.

raw measurement

The first thing that you’ll notice is that this response looks totally ragged and nasty. It’s hard to say exactly where the average is if it was ‘flat’, and there are clearly peaks and dips of 10db. That’s partly because this is a real in-room measurement, the room isn’t treated with much of anything, and it’s like a big echoing box. Concrete floor, flat ceiling, thin rug that doesn’t cover much, and not much stuff on the walls yet. Regardless, there are some good things about it. The response doesn’t drop like a rock below 30hz, and I can tell you that the woofers really made some impressive sounds in the mid 20hz range. The system can do bass, but the room still needs help. Lets see what we can do.

After collecting this data I opened the REW equalizer window, and I selected “miniDSP” as my equalizer so that the program would know what it’s allowed to do in terms of suggesting correction. I assume that some of the other selections have more or less EQ bands available. Next I had to come up with the ‘target settings’. This is what tells the program what you want the ideal system to do. I have some trouble with this one, knowing what to set. I think maybe this is where a sweep to more like 20khz would have given me more information about where the average is supposed to be. Regardless, lets give this a shot.


I picked 72db as a target level, set the target as flat with a 24 db/octave rolloff at 20hz. For a full range equalization I hear that you are supposed to set a gradual rolloff above 1 to 3 khz, but I’m mostly interested in taming room modes here, and those are all well below 1khz.

In Room EQ wizard I clicked on the “filter tasks” tab and then “match response to target”. It twiddles things around for a second, and then gives five parametric EQ settings that shifts the response to something closer to the target.

target response

Here you can see a brighter red line that is closer to the blue target, and a brownish line that’s the original response. The bright red line is the predicted response if I load the EQ settings. I’m able to save those to a text file and then use my MiniDSP software to read those, or I could enter them manually. Clicking “eq filters” let me see what those are; they looked like this:

filter suggested

Overall it’s a few sharp cuts at specific frequencies, and a broad boost at 40hz, giving the flatter response. I loaded these into the second configuration slot on my MiniDSP, and now I can flip back and forth between the unmodified and equalized versions. That has been very interesting.

Subjectively it sounds as though most of the room ‘boom’ is gone. However, I still somewhat prefer the unaltered version. The equalized version seems to take too much of the bass away. That may have to do with my target curve, or it may have to do with the settings when I clicked “match response to target”. The MiniDSP 4x10HD allows four configurations to be stored, so I could even try a few different versions and audition them each without leaving the couch.

I’m going to hopefully meet with some local audiophiles to discuss this more, and when I get a chance I’ll repeat the measurements with a few changes. Other than dialing in the available EQ, I think that my next step might be to hang up something cloth on one or more walls to absorb some of the sound that’s bouncing around. It’s a lot to research, but I’ll keep reporting back as I figure it out.


LX521 Speaker build- the Hypex multi-channel amplifier

It’s about time I had an update! This is basically skipping to the end from the last post, building cables, but I’ve been pressed for time in getting them built so I didn’t keep blogging as I went. I have a few pictures of putting the cabinets together, but it’s boring. I didn’t design that part, and I’m not a master craftsman with fancy insight into how you’re supposed to do woodwork. Hopefully the amplifier is a little more interesting.

The LX521 is a four-way speaker with an active crossover, which means that a pair of them need a total of eight amplifier channels. In order to provide uniform sound, all eight channels need to be identical. The amplifier that the designer uses is the ATI 6012, a 73 pound monster that costs about $2800. It’s an excellent piece of gear, but I was trying to keep the budget a bit more reasonable. A pair of Outlaw Audio Model 5000 could have also worked for about $1200 total, but then I’d need to put two 50 pound amps someplace. For just a little more than that I was able to put together a 25 pound amp that keeps everything in one box, and theoretically measures a little bit better. Also, I think that the more you build for yourself the more fun it is!

The amplifier I put together is based on a Hypex UCD180HG class-D module. I couldn’t really figure out precisely what their fancy voltage regulator upgrade would do for the sound, so I skipped it. If you have a dedicated listening room with soundproofing and are *really* into this stuff, then maybe you can give them a try (or go hog wild building with the Ncore modules). Now that I’ve built it I realize that this is dumb, but I used two of the 1200 watt switching power supplies, the SMPS1200A180. There is no way in hell I need that much power. Maybe I could throw a rave some day, but for now it just means that I have a bottomless pit of reserve power that I’ll never touch. By my best estimate, as loud as I’ve turned it up I don’t think I’ve used more than a few dozen watts yet. Hey dad, that means you could run these off of a solar panel pretty easily!

Anyway, on to the case and construction! I used the Modushop Mini Dissipante as the basis for the enclosure. I did some calculations of waste heat and fin area and all of that, and I must have messed up a decimal place or something, because I definitely didn’t need all of that cooling area. Oh well, I guess the parts will just last longer since they run cool.

The finished amp looks like this in my living room:


It’s just a plain aluminum panel with an on/off switch. Minimalist, right? The next step will be to make the guts look so nice.

The amp modules have a blue aluminum T-shaped piece with two M3 holes tapped in it. I decided to put all of the holes into an interface plate, and then bolt the plate to the heat sinks. First I drilled and tapped some holes in the aluminum heat sinks, as shown here: note that I used an old T-shirt to protect the kitchen table, and the glass of beer with a lime in it was in fact a mexican style beer by the local brewery, 21st Amendment.


Next I laid out the interface plate using some calipers and an automatic center punch to give even spacing. You can see that tool in the upper left corner of this picture. This is really useful for achieving a medium level of accuracy in an apartment with hand tools. It’s not like when I had a techshop membership and would do this stuff on a mill, but it at least keeps the hole positions accurate enough that I can generally get them to line up.


There are two 1/4-20 pan heads at each end of the interface plate, and if this were going to have a really significant heat load then I would have used more of them (and a different head) to ensure solid contact along the full length of the heat sink base. It was reasonably convenient though, and I’m not producing that much waste heat, so i thought it was a corner worth cutting.

The power supply module comes with six M3 screws already installed, holding a compression piece against an L-shaped plate. You have to take these out in order to have access to tapped holes to get this face against the heat sink interface plate. You could mount another way, and the manufacturer even says you can just let this thing hang out in free air, but I know that if I keep things cool they’ll last longer (like to pass down to my kids some day).


The amp module is surprisingly small for something that can do 180 watts and drive a one ohm load. I slathered on the heat sink grease before attaching them to the interface plate.


Once they’re all mounted it’s ready to mate up with the heat sinks assembly. You might be able to see that I did some really rough and rowdy countersinks to get those M3  screws to sit flush below the surface of the interface plate. I have some slight concern that some day one of them could be pressed against a capacitor and wear through from vibration and short something out, but probably not. I’m just documenting that concern in case anybody cares, and as something to think about for next time.


I know you wanted to see this all greased up. Look at those nasty countersinks! Eww!


IMG_6465 IMG_6466

There it is! Four 180 watt modules with a 1200 watt supply, all ready for assembly.

And…. Oops. I built them the same, and that’s not going to work for wiring. I had to redo one of these.


This is a really useful tool that I wanted to take a minute to talk about. This is a ratchet offset screwdriver, and it lets you reach into tight spaces that a regular screwdriver can’t reach. A well designed product won’t require this, but sometimes the designer just can’t be bothered to think about tool access… so that’s when you break this out. The best one I know of is what they used to work on medical linear accelerators at Siemens, and it’s the Chapman. You’ll notice that compared to mine, the ratchet area is much smaller, and the divisions between ratchets are signficantly smaller. That lets you reach into smaller spaces and tighten screws when you don’t have space for much rotation.

This is how I connected the mains power to the front panel toggle switch. It’s a DPDT switch rated for 20 amps, and I made sure that it was large because I wasn’t sure what kind of inrush current the power supplies would draw. As it turns out, they seem to have a nice polite soft-start, or else their inrush is much smaller than the spec sheet indicated because they’re just getting US voltage instead of the 230V that europeans are working with.


This ended up being a little easier than I expected. The power supply sends a few leads over to the terminal blocks, and each amp takes a positive, negative, and ground input for power. The worst part was all of the crimping. I think I ended up doing about a hundred crimps. There’s a reason they make machines to do that.

In the lower right of this image you can see the twisted pairs of wires going to the speaker output jack, and the black cables soldered directly to the XLR jacks. I need to go back and get everything twisted and trimmed more appropriately before I’ll say I’m done, but for now it works.


The last thing I did was put channel numbers on each of the amps so that I can keep things straight, and I checked a test signal on each to make sure it wasn’t putting out a measurable DC voltage and a full range music signal sounded right with one of my old speakers. During this step it was really promising to hear music coming out of my old speaker that (I think!) sounded better than the eight year old cheapie receiver that had been driving them.

One thing you’ll notice here is that I used blue paper painter’s tape as a temporary measure to keep anything from shorting out. The maximum voltage in here is 48 volts relative to ground, and 96 volts from the positive to negative terminals. Everything is firmly connected to screw terminals inside of insulated blocks, but a little bit of metal peeks out at the edges, and so I didn’t want to take any chances on something shorting out. The end goal is to have the terminal blocks bolted to the bottom panel of the enclosure in a neat row so that the wires can be routed in a clean and proper way.

The 120V mains line goes to the switch on the front panel using a tightly twisted pair of 14 gauge wires in some ring terminals. I used fork terminals for the rest, but for 120VAC I used insulated ring terminals so the screw would have to fall completely out before the crimped part could fall and contact something else. The rear panel has a three-prong jack, and there’s an earth ground that’s similarly connected to the chassis (you can make that out in the photo above).


The back of the amp looks fairly neat thanks to Front Panel Express making the panel for me. The large cutouts in thin aluminum and added threads saved me a *ton* of work, and I know they made it look nicer than I could have. I’ll add more labels when I’m done, but for now I know how they’re laid out well enough that a prompt of “1” and “2” is enough that I won’t plug something in wrong. If I did do that, it would blow up my tweeters.


Ok, so that’s all I’ve got for now. I’ll leave you with a cell phone picture of the speakers and amp in the living room. They sound pretty good. I hope you’ve enjoyed reading!


Dog pictures

Tonight I was looking through some of my pictures from Instagram and Flickr, and I thought, “I should totally round up all the pictures I’ve ever taken of dogs”.

This might not be *all* of the dog pictures, but here’s a quick stab at it:

Black-out poems!

My friend, Alexandra Naughton, recently created an E-book of poetry created by taking a black marker to Billy Corgan’s book of poetry. It’s a technique that’s sometimes called black-out or deletion poetry, and I thought it was a really cool idea.

I was inspired to give it a try, and so I went looking for material. I figured out that there are some emails and messages that we send and receive that have another message to show, and so I started collecting those emails .

If you’ve ever received one of those emails that make you say, “wow, this is crazy. I need to show somebody.”, then send it to me at ! If you’ve been broken up with over email, had a crazy ex-landlord, a school project partner with insane excuses, send them my way!

Have a happy new year!

Picking one day to make resolutions for the new year is not a good idea. We can do this any day of the year, and indeed we should resolve to make change whenever we recognize that it’s a good idea. What’s special about today is that we can take it as a reminder to look back, to look forward, and see our lives in a different scale of time than what we do on the day-to-day. What have you been up to for the last 365 days? Has it been a good year, are you making the most of your limited time?

I’m thinking about how it’s gone as I look toward the future. This year I’ve found a job and an apartment of my own. I’ve met many wonderful people (including Kaitlyn!) and reconnected with old friends. I’ve traveled, practiced old hobbies, and tried new things. I want to thank all of you for being a part of this, and I hope you all have a wonderful new year. Go out and make 2014 the best year yet!

And don’t forget to take pictures!

Lasers, sensors, cameras! A 3D scanning backpack for UC Berkeley (part 1)

About a year ago I was contacted by a professor at UC Berkeley who had found my resume online. Her team had produced a backpack device that was capable of collecting data to generate 3D models of internal spaces, and she needed a new backpack designed that would be smaller and lighter. I took this on as a part time project while I was looking for full time work, and it was a fun challenge. I’ve talked about this project in the past, but they finally went live with the backpack so I thought it was time for a post.

You can read all about Professor Zakhor’s original backpack on the EECS website. This is what they had before I arrived. It weighs over 70 pounds, is built to hold an changing array of sensors and cameras, and I understand that it went through many iterations and changes as they developed the software techniques that could turn the data into usable 3D representations of internal spaces. My job was to provide a compact, lightweight platform that provided stable and well defined positions for a suite of sensors. Many of the sensors needed to be adjusted to different angles to accommodate users of different heights, or movement through different environments.

The sensors on the version of the backpack that I designed include:

That’s it for now, but it’s possible to attach other pieces as needed. I sourced an embedded PC that seems to have the processing power to shove all the data from those sensors into some SSDs, and the entire collection of parts is powered by several lithium ion batteries. The batteries are an off the shelf solution, and have a good amount of intelligence and safety built in. We run the batteries in series to create a voltage from about 18 to 60 volts, and a DC-DC converter regulates this to a main system voltage of 24 volts.

Here’s a creepy render of the system on a mannequin.


Check back soon, and I should have an explanation of what each of the sensors is doing, and how I designed this thing!


Bike tour 2013, the rest of it!

One of the big differences between doing a solo bike tour and riding with friends is that when you’re not riding it seems like a lot more fun to socialize with everybody than it is to isolate yourself with a cell phone writing blog posts. Especially with a truck to move us along and coordinated meals, there was a lot less time to just sit around blogging.

Of course that doesn’t stop me from taking pictures along the way, so here are some of those!

This is one of the bridges that we crossed, and if I remember right we were able to zoom over it quite quickly.

As always, the California coast is gorgeous.


We had to stay lotioned to avoid burns.

I thought this irrigation pond was cool.

We had to cut through a field full of vegetables, and some rubber bands had spilled out onto the ground.

This is what it looked like for a while. I was glad to have far tires.

This is how I imagine touring across the Midwest looks.

Hey, free rubber bands.

Comically large taco salad.

We need all this food for energy.

This was out only link to the outside world in Big Sur. Oh, and the wifi once we got the password.


Some people have no respect!

The aftermath of not enough lotion. 90% of that was one morning before lunch.

That’s all for now! We camped three nights and did around 150ish miles, and I think I learned a lot about touring with friends. It’s fun in a different way, but still a blast!

Snap away!

I see that I haven’t posted any new projects since February, but I’ve definitely been keeping busy!

Just before my last photo post I flew up to Washington and did some photography for my friend Molly, shooting her bikini project.  Check it out!

Just before that I shot Oakland Nights… Live! on a BART train, and then right after that I flew to Wisconsin for Thanksgiving with my family. In February I scouted out a “post apocalyptic folk drone-core doom” band by the name of Feral Booty, in March I shot a power soccer match in Berkeley, and also Oakland Night… Live! in their new location!

All of these photo sessions felt like a pretty steady progression from what I’ve been up to (though flying to Washington for a project was special and out of the norm!), but things have recently started to intensify even more. In late March I got a text about a super secret event in an undisclosed location, and boy was it something! Check it out- and if you have a Flickr account and your settings adjusted for it, you’ll even see some ‘adult’ content. Some folks had taken over an old disused movie theater, and the show on stage was very “anything goes”. Very exciting!

I had one more ONL show since then, but then this week something kind of special happened. I was walking home from work, taking a different route than usual when I saw a car across from the post office that had been absolutely covered in bird poop. A family of herons had made its home up there, and somebody parked under them for a few weeks. I took an Instagram picture and got a good reaction from my friends and family:

shitty car

It was cool, but I felt like I could do better if I had the right light and a better camera. I looked up this website to see what direction light would be coming from at different times of the day (, and saw that walking there before work would make the light come in from the front of the car, the side by the sidewalk, so that was maybe as good as it was going to get- specifically really darned early so that light would have some good directionality and color. I decided that since the car could get towed any time there was no time like the present. I said, “I totally should!!” and set my alarm. It was really hard to get out of bed at dawn, but then I reminded myself, I TOTALLY SHOULD TAKE THAT PICTURE!!!

It didn’t really make me less tired, but it was enough to get me out the door.

I was borrowing a super wide angle lens from UC Berkeley, and so I brought that along and took this picture, which I posted on When I went to bed a couple of dozen people had upvoted it, and there was no count on how many had seen it. When I woke up it had made the front page, and over 200,000 people had seen it. Now, in less than a day nearly three quarters of a million people have seen my picture!! This is the most exposure, by far, that any of my images has ever had, and I’m totally psyched.

many views

DNA thumb drives: How we’ll store holographic videos of cute cats in 2030.

I was reading the news today, and I came across an article that researchers have proven the ability to store 700 terabytes of data in a gram of DNA.

This is amazing! I do not think that anybody as recently as twenty five years ago would have dreamed of where this is going. Back in 1990 the Human Genome Project set out to begin sequencing the entire human genome. It wasn’t until 1995 that a genome had been sequenced- only a bacterial genome much smaller than ours! Finally in 2003, after spending $3 billion the human genome had been sequenced by the NIH project. Some people did have an idea that gene sequencing could be done more quickly and efficiently, and Celera Genomics set out to race the Human Genome Project and sequence the genome first. At a cost of only $300 million, Celera was able to reach a draft sequence in January of 2000.

It’s not surprising that a private company taking some risks could beat a government program on cost and speed, but what is really amazing is that the drop in price didn’t slow down- it sped up. Recently it sped up a lot. For nearly a decade the cost of sequencing a given number of base pairs of DNA was falling at about the same speed as the cost of putting transistors onto microchips, improving at the same rate as Moore’s Law. In early 2008, a new generation of gene sequencers was introduced, and then things went nuts.

Today it is now possible to have your entire genome- your personal genome- sequenced for as little as $4,000, and it can be done as quickly as twenty seven hours. That’s on Illumina equipment, and they have many competitors working to unseat them with new techniques. Regardless of whether those techniques come along this year or next, I have heard talks given where folks who know the workings of the Illumina systems are willing to say that they are able to squeeze more performance and lower cost out of their existing technology with fairly boring incremental improvements, and most people in the business recognize that the $1,000 genome is just around the corner, and the $100 genome is not a crazy idea.

Probably the coolest part of all of this is what it could mean for medicine. The ability to quickly and cheaply read somebody’s entire genome would make it far easier to test for genetic diseases. Today you have to suspect a particular disease and order a test that targets just that chromosome. I once had a blood test to determine whether or not I was a carrier for Spinal Muscular Atrophy.  The geneticist ordered a test to detect the most common mutation of a specific gene to see if I was a carrier. Under certain circumstances I would have been referred for a second test that would do more extensive sequencing of my copies of of genes that produce survival motor neuron protein. These tests will not tell me anything else about my health or what I may or may not pass on to offspring.

When whole-genome diagnostic sequencing becomes common, then it will be possible to say “While we’re looking at your DNA, lets go ahead and see if you’re a carrier for anything else.. or if you’re pre-symptomatic with anything serious”. There are certainly ethical issues when it comes to messing around with our genes, but how much could it improve our quality of life when we can learn ten years before symptoms that we’re likely to be quite ill by the age of 40 with some rare disorder? What if we can devise personalized approaches that can nip the disease in the bud and let us live long and healthy lives? This could mean either chemical drugs or therapeutic insertion of genes into our living cells to change our genetic fate. My only hope is that if such things become possible, the prices will continue to drop at an extraordinary pace so that these treatments do not remain a privilege of the super rich.

Saving lives and improving quality of life is great, but I mentioned holographic videos of cats earlier and I don’t want to disappoint anybody. As the article about the Harvard team said, we are now able to store 700 terabytes of data in one gram of DNA. Isn’t that cool?

I need to go XKCD  on you for a minute to  explain this data density. The highest capacity USB drive that you can buy today (or at least pre-order) holds one terabyte and weighs about 30 grams. Imagine that you have a DNA based thumb drive that holds about 12 grams of DNA in an 18 gram container. You could put that DNA drive on your keychain, and it wouldn’t be bothered by magnets, and within certain limits the data would persist for thousands of years. Such a drive would store about 8,400 terabytes, and if you it would take 252 kilograms worth of flash memory based thumb drives. That’s equivalent to the weight of Andre the Giant at his peak fighting weight holding this rock:


How much data is that? The Blu-Ray FAQ says a 50 gb dual-layer DVD can hold “over nine hours” of HD video. Since there are 1,024 gigabytes in a terabyte and we’re storing 8,400 terabytes, that’s 1,548,289 hours of full HD video! You could watch cute cat videos for the next 176 years without pausing or seeing the same thing twice.

A Full Soccer Chair

Here’s what I’ve been keeping busy with lately!

One of the BORP players was able to get a new Quickie P200 (new to him- they haven’t been manufactured in at least five years), and he asked me to give it “the works”. I took this as an opportunity to try out a few ideas, and this is the result.

First I swapped out the control electronics for something more modern than the 1990-era motor controller, then I got to work on the welding. I posted last month about a new idea for a soccer guard that would be more robust than my stronger design, but also easier to make and cheaper. Call it Version Two- the guy who’s using it seems to like it, but I was finishing the build I realized that the design had space to evolve past some earlier limits of Version One.

Version One was my first venture into designing a welded steel structure that would receive a lot of abuse. I didn’t know how to weld yet, and I didn’t have a good feel for how tough chromoly can be. I knew that we wanted a guard with square corners for better spin kicks, and I knew that I wanted to minimize the weight and rotational inertia of the guard. I spent a lot of time doing calculations and what I eventually came up with had just over a pound of steel in the front four bars- some of the wall thicknesses are 0.035 inches! I’ll admit that I was worried that the guard might cave in from a bad hit, and so I was thinking about what I’d do if that happened.

At the time I designed V1, Kendra was using a Power Soccer Shop guard. My plan in case of damage was to be able to quickly change back to that guard. It wasn’t as good, but it was better than nothing and a lot of people had them. One very important thing for somebody playing for Team USA equipment reliability. We spent two years and many thousands of dollars training and getting to the World Cup- redundancy and contingency plans were important, and I liked the option of borrowing a guard or just bringing the old guard as backup. In the end we brought two complete chairs to the World Cup (but that’s a story for another day…)

Due to my limitations in fabrication abilities at the time, the original mounts sat directly on the P200 frame. The Power Soccer Shop guard just sat at an angle, but the convex front made this less apparent. With the flat front on the new guard I had to include the frame’s seven degree angle  to keep the front face vertical with the existing mounts. It was convenient because all I really needed was a saw and a drill, but now that I have some experience welding I saw a better way, and I saw that including a (stupid) seven degree angle in V2 was completely unnecessary. The player I built V2 for had similar mounts so the bends were required… but welds take a lot of prep work, welds are where things tend to break, and this bend is one of the most highly stressed parts of the guard. In both V1 and V2 I included extra reinforcement (more welding). Starting with a clean slate I realized that I could use a heavier top tube in V3 and skip the whole mess.

An extra benefit of all of this is that by using a round tube I was able to find a source for telescoping sizes of tube to let the guard slide into place securely. In place of four inconvenient screws to secure the guard, V3 just has a quick release pin.

You can see that I also used the guard mount to hold a side guard in place. That was an easy way to go, and I think it’s going to be sufficient to keep the ball from getting trapped. The worst part of this was trying to get the spacing between the two mounts at a close match to the guard tubes. I’ll be thinking about how to make that easier.

The player who owns this chair also wanted a rear guard. This is an allowed attachment that protects the battery box and anti-tip wheels, but also provides a strong and predictable surface for blocking and striking the ball. I’ve never built one before, so I’ll be watching closely to see how this one works out.

Each of the P200’s that I rebuild for soccer gets re-adjusted so that the driver’s center of gravity is placed right over the drive wheels. This improves traction and helps a lot for pivoting to hit the ball… the drawback is that it becomes far to easy to pop wheelies. This wastes time, makes control much more difficult, and can be really unsafe if the chair starts to run up and over the ball. All of the chairs that I’ve reconfigured to be so balanced so far have received additional anti-wheelie casters in the back. This keeps the front of the chair down, and greatly improves handling for the players.

Unfortunately, the same way that the V1 guard mounts were a product of what I was able to do with hand tools in an apartment’s kitchen, the anti-wheelie casters have been attached to the chairs in a primitive way. I use a piece of steel L-stock bolted to the back with two screws, and it takes some good hands to get the wheel on and off quickly. Most of the volunteers at practice struggle with it at first, and I’m probably only good at it because I used to do it three or four days per week when Kendra was training.

I’ve tried a couple of iterations of new attachments before, but nothing I’ve been happy with. I think that putting the wheel into the rear guard is as close as I’ve come to making it easy and strong. Here’s a detail view of how the wheel is attached:

When somebody’s sitting in the chair that wheel is almost an inch off the ground, though it’s almost touching the ground in this picture. The caster is screwed into the end of a tube that sits inside one of those telescoping sections, and there’s a screw that threads into the outer piece and pinches the inner piece. So far I’ve been able to drive the chair around over curb cuts and real-world terrain without getting stuck on anything that wasn’t an obvious problem. The next time I do this I’ll be looking for a way to have the retracted position a bit higher to be more sure that can’t happen.

That’s my latest! I’m really happy that I have a TechShop membership that allows me to have access to the right tools for the job so that I can do all of this stuff. I hope you’ve enjoyed reading about it.