Posted on

DIY Cargo Bike – Part 2

Continuing where we left off, we will start with the more fun part of welding on the cargo bed area.

      1. Welding the cargo bed.
        Like mentioned before. The bike’s geometry is made from points, what comes between them is only aesthetical. So this part was quite fun as everything that mattered had been aligned and locked into position. Basically the only thing you really need to worry about here is that you have enough space for pedals and the front wheel.
        DIY cargo long john
      2. New steerer, fork modifications.
        After this step, you will notice the progress stopped. The frame was left unfinished for almost a year before having time to continue. As a next step all the excess was cut off, and the head tube [guide to frame tubes] shortened. Also the fork got modified to fit 20″ wheel as originally it was ment for 700c wheel, and disc brake mounts added. It’s important to check that you don’t make the fork too short or too long, so the cargo area will be parallel to the ground. Now I finally also cut away the extra parts of down tube and fitted a new steering tube. I went for A-head stem for this. This bike was an experiment and I didn’t want to spend time and money ordering specialized fancy tubing. So I found some precision tubing that fits the stem and the head set from Onninen. It is quite heavy with 2 mm walls, but as I knew I would make it an e-bike, the weight was not too big of an issue. Improvements for next time: Go for Chromoly steerer and head tube to save some weight. Order early in the process.
        DIY Cargo Bike
      3. Outsourcing lasered parts.
        Now you could do this on your own, but I saved a lot of time and also made things look nice by ordering some of the parts lasercut like fork dropouts, steerer end, bearing holders for steering arm etc. You can find my DXF files here if you find them useful.
      4. The finishing touches.
        At this stage I bolted on a bottom bracket, cranks, an old chain and went for a test ride. Everything felt nice, so the only thing left was to weld on last tubes, disc brake mounts (you can find mine under the above link), cable holders, kickstand and then it was time for the paint shop.
        DIY Bullitt cargo bike
      5. Assembly day!
        After everything arrived from powder coating, it was finally the time to assemble everything. All went smoothly and the bike was in one piece in no time.

        View this post on Instagram

         

        A post shared by KP Cyclery | KP Cykler (@kpcyclery) on

         

      6. HOUSTON, WE HAVE A PROBLEM! (and cure)
        Early testing revealed some flaws I had described in the last post about handling. After hitting 30 km/h the bike almost always got hit by speed wobble. With this problem, the bike would be rendered useless. Luckily I didn’t get discouraged as even the guys at Larry vs Harry also seem to have a problem with this, and the cure is to add a steering damper like the one used on motorcycles. I ordered one and attached it to the bike, and..    ..it actually solved the problem for a while before it broke down and leaked all the oil out after just 600 km on the bike. Then winter came along and I left the bike unused until this spring. After talking to some other frame builders I heared that this problem was common, many of them had also been fitting their bikes with steering dampers. The problem seems to be that the front end just gets too light as the problem is less evident with cargo on the bike. Anyway – I set to work early spring and made new damper fittings that would increase the working range of the damper. Having now done 500 km at speeds of 35 – 60 km/h without any steering wobble it seems that the bike is finally finished. Improvements for next time: a.) Design your bike with steering damper in mind from the beginning. b.) Keep shallow fork angle, short fork rake and thus a large amount trail. This may improve stability if you want to resist using a steering damper.
        DIY Cargobike KP CYCLERY

To summarize, this project turned out a lot better than I had anticipated. Before setting to work, my mind was set at 50/50 chance that the bike would work as good as it does. The Bafang 750w electric unit works well, the geometry is working with the steering damper, there is plenty of cargo space and it goes as fast as you wish. The mileage speaks for itself – currently I’m averaging 150-200 km per week and only use the car for a short ride once a week to keep the brakes from sticking etc. So if you have some welding skills and you’re thinking about building yourself a cargo bike- GO FOR IT! Also as a side note, we are constructing a jig to weld some more frames, so you will soon be able to order a proper cargo bike frame from us 🙂

And here it is – doing 45 km/h:

Posted on

DIY Cargo Bike – Part 1

KP’s home-grown cargo bike anyone with an angle grinder, old steel bike and welding machine can make without any special tools.

Firstly a disclaimer. As this bike was a personal experiment then I didn’t use the regular amount of planning and modelling. Many methods would not be used to make a proper product and currently I’m constructing a jig to hold everything in place when making this kind of bikes in the future.

With that cleared away, let’s dive into this DIY Cargo Bike project. It was actually started 2,5 years ago and I finished the bike roughly 8 months ago. I wanted a long john type cargo bike when we decided to move to Estonia, as there will not be a luxury of so many cycle paths. So already when still in Copenhagen I started the project.

  1. The geometry.
    Something that irritates me a little when people see my bike is they say – oh did you make a Bullitt replica. In part that is true. But also true is that long john type cargo bikes were used a hundred years ago, so you shouldn’t be afraid to make something similar. Of course most of the geomtery should be similar to an existing bike that has been tested and sold with success. So you can use a lot of the geometry here: http://larryvsharry.com/wp-content/uploads/2014/08/technical_wireframe_bg1.png
    Improvements for next time: a) Plan as much ahead as possible. If you have access to 3D CAD program then use it. Model everything, check that nothing collides when steering etc.
  2. Chopping an old bike into pieces. Welding a new down tube.
    I knew I wanted to do as little work as possible, so I found an old bike, dissembled everything and started cutting away. After cutting away the down tube I took a long 2 meter tube I wanted to use for the new down tube. Then I aligned it to the middle of the fork and welded to the bottom bracket. It is important to keep the fork on the bike at this point as I was not using a jig and needed some reference points. Keeping the new down tube long would also be giving me reference points for later alignment of the new fork. Before welding, I made sure the seat tube and new down tube were parallel by bolting both the welding table. PS! If tubing sizes are different then you need to use something for distance under the frame tubes if frame is of smaller tubes. Improvements for next time: a) I would consider building a jig even for 1 piece. b) If not then I would run another tube under the down tube to align the new down tube with the rear axle center. c) I would make the down tube from round tubing as it will have some rotational stress.
    DIY cargo bike
  3. Welding on a new top tube.
    Now I cut off the steering tube and cut the old top tube shorter, using it as a guide for the new top-tube alignment. This way I could make sure the new steerer would end up in the middle of the bike. Had I used a men’s frame I would have probably kept the original top tube. Note: keep the guiding tubes on the frame as long as you can. They help against heat distortion from welding. Improvements for next time: a) Make this from round tubing for more resistance to rotational forces / torque.
    DIY Long John Bike
  4.  Welding on the new head tube.
    Now this one was the biggest mistake and can also be for you, so pay attention and read improvements. Steerer postition will affect the whole handling. So what I did correct was to make sure the head tube is in position before welding the cargo bed. All the tubing in between the bottom braket and head tube can be misaligned without a problem – if the head tube, rear triangle and the bottom bracket are located correctly. So using the 2 meter long new down tube, I could be quite confident that the middle of the front hub would be in the correct position. But getting the fork exactly straight in relation to the frame is more tricky. I used an extra piece of tubing and welded it to the new down tube. The other end was bolted to the fork.
    DIY cargo bike 5
    Now I didn’t double check the alignment properly here. I would strongly suggest using an inclinometer here. Or at least a spirit level to make sure the seat tube and head tube are aligned. Next comes the head tube angle. You need to make sure you have proper amount of trail in order to keep the steering stable. I didn’t pay enough attention to this and ended up with almose half the trail of a Bullitt (more about trail and steering here). Improvements for next time: a) After setting up the fork take a photo of the frame as best as you can from the side. On your computer open the photo with image editing programme and calculate the head tube angle or just compare it to this blue print of a Bullitt. b) I would buy an inclinometer from the web to check all angles. They are quite inexpeniseve , starting from 10€ on the web.
    DIY Cargo Bike Trail
  5. The Problem.
    I mentioned a the steering will be where you can make the biggest mistake. What I ended up with is speed wobble when running over bumps at speeds over 30 km/h. Science is not exactly sure why it happens. In my case I think it is small trail combined with slightly misaligned front and back wheel and square tubing for top tube and down tube which make the frame flexible sideways. What I did to compensate is that I added a motorcycle steering damper. This worked, but I want to experiment further. This year I will cut the fork again and try to increase the trail. I will post an updated later this year whether this worked. I believe Bullitt actually also has trouble with high speed steering stability as they also now have a steering damper for as an extra option.

To be continued…
KP

Posted on

Hey kid, you’re hired!

The interweb is a vast place, and every once in a while you tumble on something hilarious.

We’ve never thought of opening an electric bicycle division, but maybe we should..? If only we could hire this kid.

Check out his ingenious homemade eBike. We can only imagine lawyers taking their electric-drill-powered bikes between their meetings.