Wednesday, May 15, 2013

Part 1: Home-built Xtracycle/Big Dummy seat

The rear seat as it has evolved after a few years and thousands of miles of use.
For a while, I've been meaning to put together a post showing how I built a kid seat for the deck of my Big Dummy. The thing is, I built it prior to the existence of this blog, so it was not well documented, and factor that by my inherent laziness. That 'while' has now stretched out into a couple of years. However, recently the rusty gears in the task completion part of my brain have been jarred loose, in no small part because fellow Daddy and Big Dummy owner bikewRider has inquired as to its construction. He is in need of a means to transport his little wRider, and, not too far down the road, a second co-pilot still in development.

That said, this presentation is for entertainment purposes only. I make no claims as to the safety or reliability of the cobbled together device pictured here, nor for the appropriateness of any use thereof. I am at best a middling craftsman and have been known to use materials and resources for purposes other than that for which they were originally intended.

If, against better judgement, you proceed to construction of something similar, any outcome, whether good or bad, is entirely of your own doing. I assume no responsibility. Know this: a healthy dose of common sense and constant attention to the safe operation of any machinery is paramount. You have been warned; proceed at your own risk.

Another view of the seat.

On to the show. This is Part 1 of what will likely be two, or if I get ambitious, three parts. The focus of Part 1 is to show how everything goes together. There are a total of four wooden elements in the following construction: 1 deck, 1 backrest, and 2 side panels. A key element that allows the deck to support a vertical backrest are deck wings. Don't worry, they'll become apparent in the following photos.
The underside of the deck, removed from the v-racks. The deck wings protrude from each side. Note that the Xtracycle Magic Carpet cover  doesn't interface well with the deck wings. That part at the top is for a second seatback that I added after initial construction. Just forget about it for now. We'll come back to it at a later date.
Side view of how the deck wing supports the side panel.
I added a bit of lateral curvature to the backrest. It's constructed of two 1/4" pieces of cabinet-grade oak plywood laminated together. I glued and clamped them to a form in order to produce the curve. 
From left to right: Magic Carpet cover, closed cell foam pad, seat deck assembly.
The basic shape of the deck and the SnapHook holes are traced from the standard Xtracycle Snapdeck. Again, the deck is comprised of two laminated  1/4" layers of cabinet-grade oak plywood. I used four Xtracycle SnapHooks for attachment. If I were to do it again, I'd use the newer SuperHooks, which were not available at the time.
Another view of the deck assembly. I would have preferred maple or ash to the oak, but it was what was available.  
Here's the assembly on the bike without the Magic Carpet. Notice the backrest is above the deck so that there is space to clear the closed cell pad. Note the side panels are from scraps of exterior-grade 3/4" treated plywood, not the laminated oak of the deck and backrest.
The backrest rises to about 12" from the deck. If I did it again, I'd go to 15 or 16 inches to better support sleeping, bobbing heads. I might also make actual armrests on the side panels. My philosophy was to keep everything smallish, so as to retain maximum usefulness of the deck without a passenger. However, a little larger wouldn't diminish any utility. 
About 10.5 inches across the back. This width seems good for a wide range of differently sized passengers.
Wingtip to wingtip is about 12" on the leading edge. I traced the original Snapdeck on some paper and sketched in the  deck wings, then transferred the design to the oak plywood for cutting. I based most of the dimensions on careful guesswork and measurements of various kid-sized devices with seats. 
The trailing edge of the wings are narrower, so that the effect is that the seat sides open toward the front. Note that the strap shown serves to more strongly connect the deck to the v-racks. 
I glued and screwed the backrest to the side panels, being careful to pre-drill pilot holes and apply glue to the screw threads. That sucker is there to stay. The backrest makes a great sticker board.

A view of the deck wings. Three glued screws per side. I think all the screws that I used were 1 5/8" exterior grade.
This shows the laminated layers of the deck. I cut each layer separately, glued them together, then sanded them evenly along the edges. A router to round the edges would have been nice. 
The length of each deck wing corresponds with the width of the side panel. I angled the side panels at about 10 degrees, so as to make the backrest a bit more comfortable than a right angle would have been. If I were to do it again, I might go for a 15 degree lean. My compound mitre saw was helpful for making these cuts.
Side panels are about 9" high. 
An overall shot with the ruler to show how far back the backrest is placed.
That's more or less it for the basic construction of the deck assembly. Pretty straight forward; just measure and cut carefully, and if in doubt, build a cardboard mockup. After the initial assembly, I sanded off any rough edges and applied four coats of exterior grade polyurethane to all surfaces. After four years of a lot of use and spending a fair amount of time outside, it's holding up well, but could benefit from a refresher coat or two.

Next up: Seat harnesses and cockpit amenities.


  1. Thank you! Thank you.

    I was in the backyard this afternoon with a snapdeck, a saw and plywood. I was trying to guestimate the seat dimensions based on the age of you daughter and the pictures in your last post.

    I was so close to emailing you just to ask for a few measurements.
    I know you're a busy man, so I refrained from harassing you, knowing it was already on your to do list.

    The 'wings' are the secret I hadn't been able to completely figure out from previous post.

    Thanks for sharing, I'll be sure to share what I end up building.

    Coen has done great riding around sans seat, but it will be nice to have something a little more secure and laid back for him to tool around in.

    1. Happy to oblige. Riding with kids on a longtail is one of the finer things in parenthood. I look forward to seeing your creation and the adventures you and your little ones take.

  2. Ha ha! Awesome. I think I was going to figure out how to rig a folding camp chair on there for Aida, a-la Candahoovian TSBC member Jun's solution here:

    I got to get on this though, along with all the other projects.

    1. I like that camp chair idea. It seems very practical for nearly grade school aged kids.

      The time investment to make accommodations comfortable for young co-pilots is well worth the benefits. It will be cool to see what you end up making.