Bullit II Build Series
Part 3 (you are here)
This Is The Big One…
Crawling thru the bike starting from the back of the rear rack, we’ve worked our way forward to the cargo box area. This is where all the real work – and all the ‘oops’ and ‘uh-oh’ – happened. I will mostly skip the wrong turns and instead focus on what worked.
Because so much went into doing the basement, and it was a primary objective in this build, this post will be focused there and be talking about just the floor, and boxes underneath it.
The Main Bullitt v2.0 Objective?
Hide the damn battery box. Thats it in one sentence. Lets look at what we did last time. Here is the v1.0 battery box on the Lizzard King.
I say “in case you miss it” above only half kidding. A lot of people do miss it. Maybe they see it and mistake it for a deeper cargo area. It isn’t. It is beneath the floor, hangs under the frame and holds a heavily padded, large battery.
People often make the mistake of thinking it will scrape the ground. It doesn’t. In fact its never touched anything in more than two years of service. But… the bike would look cleaner without it.
Here is what it looked like inside a couple of years ago when I bolted it shut for the last time.
Figure 2: If you want to see more on this bike, with all the details of the battery and whatnot, the whole build process was documented here.
Worth noting: Before I did that final bolting-up, I had already checked after a few months of wet and dry riding. No water or crud was making it inside.
Lets skip to the end and see the result:
The battery box is there, but this time you can’t see it. In fact, it holds an even bigger capacity battery this time (it is physically smaller. We’ll get to that later).
There isn’t just one box. There are two. The one in the back holds the battery. The one in the front holds the front motor controller and a weatherproof onboard charger. I plug the bike straight into mains power.
It came out great. It was a bitch getting it there, and I didn’t know if my underlying idea would work until well into the project. If I ever do a Verson 3.0, it will be a by-the-numbers assembly. But I plan this bike to last my lifetime and have no desire to try again. You, on the other hand, are free to do your own and not make my mistakes. So lets begin.
Lacking machinery, materials and fabrication skills up to this task, I took a tape measure, did some measuring on the Lizzard King (my new frame was still in transit) and started some research. Then I got on the internet looking for made-to-order, simple metal work. I found metalscut4u.com after some googling. They had an online project configurator. I ended up using it to quickly draw up what I needed and placed a work order.
Are they the best choice (especially versus a local machine shop)? I don’t know, but they were the best option I could find, even if the project was a bit pricey. They shipped promptly and the product was exactly to my measurements.
I didn’t order actual boxes. Instead I used what are described as ‘hat channels’: a single sheet of aluminum, with 90-degree bends in a sort of inverted hat shape that is open on two sides. It was a simpler and cheaper job. My thinking was some special needs to fit the Bullitt frame would make it easier to adapt a hat channel into a quasi-box, with extra-thin, short sides I’d put in myself.
Figure 4: Length and width as-received. The creepy selfie at left is a bonus.
Since the shop and I are both in the USA, the order process used Imperialist measurements. The hats are 8″ x 15″, with the hat ‘brim’ – the wings that support the box hanging on the frame – at 1″. These measurements are internal, and this matters because the alloy is 1/8″ thick, so outer dimensions are a bit wider as a result. Its the outer dimensions that decide whether the box fits inside the frame.
How deep are they? Its been so long since I did the actual work (8 months as I write this), I don’t quite remember. Roughly 3.5 inches? Don’t pay attention to that as you will need to measure your own battery, and figure out what a second measurement will be in the following next step. Those two taken together, and factoring in your steering arm placement, will decide box depth.
With all the talk about inside and outside measurements, lets touch on the box thickness. On the Lizzard King, that box was purchased as-is, and it uses alloy that is probably 1/16″ thick. Its thin, lightweight and sturdy enough, but not enough to be confident of it withstanding impacts. Thankfully it never has hit anything.
Since I was using a 3rd party metal working service, I had to take what I could get in terms of the thinnest alloy they offered, which was 1/8″. That is twice as thick, and twice as heavy. But its alloy so not that much weight, really. The thick walls make for a lot of strength. Having boxes with both thick and thin material, I’m a lot happier with the thick stuff.
Put The Sides On
I already had a long strip of 2″ aluminum, 90-degree angle bar stock in very thin 1/16″ size (sorry again for the units but to be precise I’m describing it exactly as-sold). I also had a good supply of Shoe Goo, which is a super-strong adhesive that permanently, totally bonds almost anything to almost anything else.
The idea was to cut a precise strip that covers the outside width of the hat. Glue it to the hat both from the underside, and along the vertical edge, which has 1/8″ inch of full edge contact, plus a bead running up along the inside vertical edge. This forms a bond that may as well be welded on.
Attaching the angle stock with glue from the outside preserves the unbroken box surface, and leaves the inside perfectly smooth. It can’t leak if there aren’t any holes. There are no wear points to rub on, like a bolt head or rivet, if there aren’t any. Plus… every millimeter counts when it comes to vertical space. Bolt/rivet-free attachment from the outside reduces internal vertical space by exactly zero.
If you enlarge Figure 5, you can see the underside portion of the side pieces are filed shorter. This keeps them from extending past the curved, bent bottom: No edge to catch on.
So much for the back box. The front one is more complicated: The Bullitt has mounts for the side panels in that forward space. You can’t just drop a box into it. This is a big part of why I used ‘hats’ instead of boxes: The need to hand-fit this part. Figure 8 below shows the job fully done.
To clear the side panel mounts, I marked the hat with circles matching the position and outside diameter of the side panel fittings. Next I took an angle grinder and sliced into the marked area in a very rough arc marked on the hat, taking off (hacking) material close to but not crossing the marked line.
From there, the arc was smoothed by hand with half-round metal files. After a fair amount of filing, test fitting and filing some more, I had enough material removed to fit snugly into the frame.
In Figure 7 above, note the box is shorter than the frame width, and is pushed all the way to the left. The idea was to use that gap for running cables in what will eventually become a deep channel.
After the holes were complete, the next step was to cut shorter side plates that accommodate the side panel mounts. It was important to give the adhesive plenty of time to fully cure, so that was a couple more weeks of down time. Figure 8 below shows the boxes ready for primer.
Primer and paint
Figure 8: Not so sloppy this time with the adhesive. Holes match the Bullitt’s crossbars and will be enlarged later
The next step was to primer both now-completed pieces. Both were roughed up considerably with a random orbital power sander for better primer adhesion.
I spent some time deciding whether to paint the boxes gloss white to match the frame, or a stealthy black. The latter won out and, after a week or so to let the primer cure, I rattle-canned on a couple of coats of satin black automobile engine paint
Other Parts Of The Equation
Referring back to Figure 2, you can see the Lizzard King’s 32ah battery was so big it would have never fit between the frame crossbars. It had to be slung underneath. That was battery cell reality in 2021. Further, because of the Bullitt’s steering arm, the underslung box could not be very wide to let the arm move while steering the bike. Thus you see a battery mounted lengthwise, on a narrower box whose drive-side edge is diagonal and not squared.
This version has to be shallow to fit above the steering arm. That lets you use the full width of the frame space. But it creates a box not deep enough to fit a battery under the floor.
Unless you raise the floor. Thats the key idea – and its not just my own. I’ve since seen other Bullitts where the same thing is done.
The Bullitt’s factory honeycomb floor sits below the top of the frame rails. So we can raise it higher. That increases the effective depth of the box. But the honeycomb floor is quite thick. Millimeters count. The dibond floor sold by Velution is very thin, strong and lightweight so I used that and gained more space.
How Do We Raise The Floor?
That is a fiddly little job to get right. The box lips themselves will raise things up 1/8 of an inch. But where the two overlap between them, its double that height. To even out the rise on all three crossbars, I used a 1/8″ drilled alloy strip. You can see one at the bottom of Figure 7. One goes on the front and the other on the back.
But thats still not enough for the floor to clear the battery. Wood strips cut, drilled and treated against weather were the lightweight answer. I used Home Depot to source those.
Is It Going To Fit?
Before I got to painting the box or affixing the sides to the hats, I had to do a test fit to prove the concept. I dropped in the hats, plunked in the battery, taped on the spacers and…
It Fits. Now What?
After the test fit, knowing it was very close out of the gate, it was time to do it for real. That involved a whole lot more effort.
This is a task a good builder never takes lightly, and can be a nightmare on a 2wd system. Mix in the length of cable runs required by a Bullitt frame and it was a lot of tedious work. I bought a stack of HIGO cable extensions in advance, ordering double what I needed. It turned out I used all of them.
To prevent water/sand ingress I used two different types of automobile door insulation – the big rubber seals that run around the edges of car doors. It clamps itself to the tops of the box sides.
Figure 11: At left is the charger AC cord exit. At right, the wood strips, seen treated with an ugly water repellant wood stain. The one on the right is chewed up and only used for testing during the build.
In Figure 11 above, the power input cord for the charger had to exit on the non drive side. I used slit silicone hose to cover the bare (filed smooth) edges of aluminum the cable contacts. You can also see the car door insulation sealing the top of the side edge.
Final Bits and Pieces
Also seen above, the charger is already bolted on. The controller is about to be as well. It and the charger’s undersides were lined with thermal transfer tape, to enhance heat transfer to the thick aluminum box.
You can see in Figures 11 and 12 how the slightly-shorter wood slats, and the offset to one side, creates a channel for cable runs.
You’ll have to scroll all the way down this page and look closely to even see this one: The boxes are not level to one another. The forward box (which doesn’t need as much depth) is sitting on top of its 1/8″ alloy spacer strip, and on top of the ear of the rear box. So it sits higher. The rearmost box needs every bit of space it can get, so it sits directly on the frame crossbars.
The battery is fixed in place with small bits of super-dense closed cell MinicelT-600 foam.
The battery fits so snugly in the available space that cable routing was difficult. The charger cable was split to two lines – one forward to the charger, another rearward to the top tube bag for an aux charger if needed (like a Cycle Satiator doing an occasional precise balance charge). Battery output also had to be split to each motor, front and rear.
The Wood Spacers
These were bolted directly to the frame, and further clamped by bolting the floor on top of them. Not in the pictures: I used a layer of hard rubber adhesive stripping, 1″ wide, atop the wooden slats. That provided the final bit of extra space to let the floor lay flat without bending it over top of the battery pack.
The short wood spacers at left in Figure 12 are sitting on a layer of that rubber adhesive, with more adhesive squares on top sides for proper leveling. You can also see big, loose zip ties that have not been trimmed yet. Those are cable guide loops for wires – insulated in silicone tubing – that run underneath the floor.
The front box does have two open holes thanks to the frame’s side panel mounts. The charger and front motor controller are both IP65 rated and can only benefit from some ventilation, so this is not an issue.
The Floor Goes On
I planned from the beginning to use extra clamping to the floor. I don’t want to see a giant battery bounce into sight. I added four additional bolts. The foam pads on the Velution floor that cover all frame contact points are already cut to match the frame holes. So I knew where to drill without having to measure.
Figure 13: The floor is on, and staying on. I lined the edges of the floor board with rubber channel liner.
The floor has countersunk holes pre-drilled into it. I wanted to spread out the clamping force, so I used some extra-wide countersunk washers from MacMaster-Carr. I also needed two sizes of extra-long countersunk M6 bolts from the same source.
The Floor Attachment Tweak
I expected that raising the floor had one consequence: The holes would all line up, EXCEPT the two on the forward bulkhead, behind the front wheel. Those would be up high and no longer match the frame crossbar holes.
When I was thinking this issue through, I didn’t yet understand how simple it is to drill thru dibond floor material. What I should have done is just drill two new holes, and plug the factory originals. By the time I realized this, I had already bolted the floor on. To undo that I would have to take it off again. The gymnastics needed to get bolts, washers and nylock nuts together in between those two boxes… No thanks. So I stuck with the original plan.
My first solution involved making two patch plates for a second bolt to fit through the original floor hole (the bottom bolt and patch plate are tightened on before the floor is bolted down).
A few days later, I realized a spacer block from Velution that I hadn’t used made a nicer substitute for the patch plates.
In this picture I just fit the spacer blocks with a stack of washers. Once fit, I measured the space and replaced that stack o’ washers with a single black alloy spacer that bridges the gap precisely and cleanly.
Plug in the charger via an External panel plug
I bought and still have the C14-type panel-mount plug for this. I’ve seen other Bullitt battery boxes do this, but they are not hidden between the frame rails, so they plug in on the right or left side.
Since my box sides are hidden, I could only put the plug in the back. So I have to get down on my knees every time to plug in the charger. Screw that. Plus I did not want to cut holes in the boxes. You need a hole to have a leak.
Interconnect the boxes with a tunnel to pass wiring between them
The sheer size of the battery eliminated this idea. I had a plan… but then the battery arrived. And the hats arrived. And I saw there was no way anything would fit unless it was just a pair of gasketed open holes. Nope.
Make a 1-piece double-hat box instead of lumping two next to each other
This didn’t happen for one reason: Money. This would take the project out of the realm of a cookie-cutter web site configurator’d project and make it a custom-consultation job. Someone with better fabrication resources or abilities will want to do it this way but it was a bridge too far for me.
Make cuts in the box ears that interleave the two sitting together
Neat-o idea. Sounded great sitting and thinking about it. Then I got into the actual build and had 40 things to do, and this was a great big #41. In the end simply adding two alloy strips of an equal 1/8″ thickness on the front and back dealt with the issue just fine.
We’ll talk about the custom battery, the onboard charger, the cargo box liner, the front wheel and a few other bits in Part 4 to wrap discussion of this bike up.