Why a carrier?
I want one so that instead of taking my stuff to work in a backpack I can put it on the carrier. It can also be used for shopping. I bought one but it is tiny and not very straight – considering the size of my bike it will probably need a special design anyway.
Time to make my own. I started by designing things in Blender.
Carrier design Mk.1 and 2
Model 1 was designed using hollow extrusion for the frame. This was fine apart from the need for longer bolts. Then I saw a battery pack designed to fit a rear carrier that had the rating of 36V20AH which is more than my current pack, so I decided to make Model 2 which uses “L” section parts and thus has a hollow inside that fits the new battery pack.
I am still not sure that I will buy it but I have not cut any metal yet either.
Carrier Mk 2
Mk.3 Carrier
I thought some more about the design and figured it might be better to make the frame from one part and bend the corners if possible. This would mean getting a solid tubular object to bend around but there are big gains: a lot less nuts and bolts and hole drilling, smooth rounded corners that won't catch and a weight saving. Provided it can be bent neatly it will be well worth it. I would need to do a test bend of course.
Carrier Mk 3
Mk. 4 Carrier
I thought about it some more and realised that I will probably want that larger 20Ah battery pack so I redesigned the carrier to suit that option – as well as making it a little easier to fabricate by only having two bends instead of four. A second copy of the frame could then be added on top to make a hollow carrier to allow sliding the big battery pack in while still offering cargo space on top.
I found some brackets that will fix the carrier to the frame very well – pipe clips that arrived quickly. I had to buy a whole box of various sizes but so what? They were cheap. They are stainless steel strip with holes at the ends in a “b” shape that can be put around a tube or pipe and they have a rubber pad to insulate them. I can probably use them to fix other addons to the bike too.
The Mk.6 Carrier
I realised the best way to make the carrier was to make it from angle with the flat ribs protruding so that a cargo box can be slid onto the rails as required. If the ends of these are rounded then they are safe without needing the complication of curving metal corners.
The Cargo box could then have a frame of flat metal bars attached to the bottom with slots that will slide onto the rails and lock onto the carrier. The holes are probably going to weaken too much although they look neat.
After a lot of money spent and messing around I gave up on the idea of chopping the extrusion with the power saw (don’t get me started) and cut all of the parts for the carrier with a hand hacksaw. All went quite well. Then I had to go buy a new set of drills since the one I wanted was blunt and I have no sharpening equipment.
Then I had an idea: why not superglue the parts together instead of bolting everything? It is simpler, does away with the problem of drilling aligned holes in parts and is light.
Glued and painted the parts. Painting with spray cans turned out to be harder than I expected though: lots of it went into the air and after I had finished I discovered areas that needed more - well, I am no expert with spray cans. I might need to sand the parts and repaint them.
I will make a box up as a spray booth to cut down on the waste spray too.
Next Morning, the painting looked terrible. I had to wet sand it all to get a smooth surface and lots of it just came off way too easily despite me sanding all of the bare metal with P800 before painting. The “self priming” paint just didn’t quite work out as expected. There are a few reasons why it failed: first, my own incompetence at spray painting with cans. Then there is the conditions: hot and windy out in the backyard so a lot of paint never reached the things being painted, the parts all hung loose from wires which meant they moved about, and finally maybe the surfaces were not as well prepared as I thought.
I began wet sanding it all down with P400 and after a little pressure the glue joins popped apart. (At least it didn’t happen on the bike.) So now I need to drill and bolt all of the holes as originally designed and finalise the parts, then rig the finished parts in a wire frame and repaint them.
It would have been a good idea to drill all of the bolt holes while the parts were glued together: that would have guaranteed that the holes all lined up. Sadly I didn’t do that but I got them right with care and patience. Lots of patience. The parts matched up by glue areas – I could see where some glue stayed on one side and some on the other so by matching glue patterns you could fit it back together. It all bolts together and after some on-bike adjustment it fits on. Now just one small puzzle: identifying the parts. When I go to repaint them (properly this time I hope) I need to mark them so I know which part goes where since the hole patterns are not exactly the same. Some surfaces don’t need paint and where they meet up no paint would be better so in theory I could write the markings there and then cover those areas with tape.
The final fitting of all parts on the bike showed that I could fix the small support bars to the bolts at the front of the carrier rather than drilling more holes. All of the support bars only got their top ends drilled and lengths cut at this point - regardless of how well you might design things in CAD, nothing beats actual fitting.
I wired the carrier parts into a frame for painting. I did this so that they don’t move around as I am spraying them, something that happened in my first paint spraying.
I was also more careful about heat and wind so it worked out right this time.
Assembled everything today. The paintwork is still not great in that it is easily scratched, which I did during assembly. Never mind. It is good enough. It’s strong and solid.
Here are two pics of the carrier before I added the mudguards.
It is held together with M4 bolts and nylock nuts and is fixed onto the back of the frame with two pipe clamps under the seat and two M5 bolts to hold the side bars on.
The back mudguard bolts into that hole in the middle of the carrier.
As a bike to get me to work and back it is real good. Yes, it still looks better without the guards but that doesn’t stop the rain coming down.
This is the final design done in Blender of the carrier made from aluminium extrusions from the hardware store. The parts are few and I could carry them all in one hand easily.
The main rails, ends and right- angle joiner parts are all cut from 30 x 30 x 1.5 mm “L” section. The main supports are 15 x 5 mm bar. Everything is held together with M4 stainless bolts and nylock nuts.
Considering that you can’t buy a carrier to suit a bike like this (well, not that I have seen), and how cheap the materials were, it was a pretty good project to spend a weekend or two on.
If you want to build your own, drop me an email and I’ll send you some plans and a parts list.
