The Locust – The Low Cost Tadpole Trike Project
Article by Emma “twinkle “Wheatland
It started one Saturday afternoon late last year after I collected a couple of disc braked suspension bikes from the tip (local landfill). As usual, I started to chop the bikes up by execution of the head tube and the top parts of the suspension mounts from the frame.
However, before I ran the cutter through the rear end, I wondered whether it would be possible to make virtually all of a trike frame from the scrap that lay around the workshop. That is how the low cost concept came about. Subsequent visits to the local tip provided more parts.
The Locust DIY Tadpole Trike
I am a firm believer in fitting a new drive train on all my trike build but, unfortunately, it bumps
up the cost: three chains, a guide pulley and a freewheel unit, new cables, spherical rod ends and a few other new bits. On the whole, I have tried to keep the cost as low as possible without compromising on quality and reliability.
After laying out the rear end on the bench and measuring it up, I found that a 41" wheelbase straight boom trike was feasible without cutting and joining the main boom. The down tube of an oversize
standard MTB would provide the front sliding boom assembly, at the same time I got a child gate from the tip that gave me the 50x20 mm square tube for the cross boom.
The main parts of the frame
The centre joint must be very strong as the force that the legs can exert could bend or at least distort the joint, so a reinforcement brace was fabricated that would join the front to the rear through the cross beam. It would give the necessary strength needed to survive. After a little thought, we came up with the design of a one piece crucifix with a sliding adjustable front boom.
Once the frame was welded up, the whole frame seemed very strong, but there was some flex and the frame might not be suitable for anyone over 185 lb. It would require using larger tubing. However, using a larger tubing has other issues that would cause mating problems between tubing.
The completed frame
The frame only took a couple of days to jig on a flat surface and weld up. The seat mounts were added with extra gussets to strengthen the odd shaped joints. I had some round and square plastic tube caps so all the tubes were plugged by caps to save time and gas.
The main tube had the caster angle cut into it and the camber was cut into the cross boom. This made setting up the angles much easier than the standard method of a compound cut on the cross boom. The reinforcing tubes were also cut to accept the caster angle and the cross boom was drilled offset to receive the centre tube and line up with the caster angle cut into the main boom.
This strange looking joint is the centre “backbone to the frame and its construction needed to be very
Square tube steering boom
The seat tube was a part of an oversize BMX frame that was still in the bits box and some off cuts of steel were used to make the seat mounting plates.
Seat mounts added
The pulley mount was made from a “double length studding connector welded underneath the main boom. I have used the standard “U” nylon ball raced pulleys on my builds and fitted a chain guide under it to stop the chain derailing over bumps.
I always use black nylon 20mm conduit for the chain return and the associated clips to mount the tube to the arm that is welded to the frame. This material has proved to be robust and quiet in operation.
Standard Street Fox style brake arms and direct knuckle steering handlebars were fitted with a pair of caliper brakes that were removed from a scrap child’s bikes and used with some matching brake levers from the MTB. On this build, we decided to use left and right hand braking and a parking brake controlled by a gear lever. The front and rear changers were controlled by a new double stem mounted levers as the pull-back-towards-you-when-changing motion does not affect the steering. All the brakes and gears were connected with new cables again for reliability.
Adjustable pedal boom
One of the scrap MTB frames gave its down tube for the front BB boom and, by chance, we found a seat pin clamp that fitted on the down tube and this gave the sliding pedal boom a professional looking adjustment clamp together with an easy method of adjustment.
Using a down tube has one slight disadvantage because the adjustable bearing cup is behind the
chain wheel. The front wheel tab angle was jigged up using the same method I pioneered on the transportable using a wooden jig with the jig clamped between the axle tab and the cross boom.
Using a jig
As the disc brake rear triangle was destined for another build together with the disc brake front hubs that would be modified for 14mm spindles, we used a spare 24” rear wheel with its own triangle and standard vee brake, on the rear wheel we fitted a 6 speed freewheel and a triple chain set up front.
The gear ratios should be adequate for a general purpose trike. The front wheels I eventually fitted were left over from the green Street e-Fox after it had its disc brake conversion as these were only a few months old.
Plywood seat form
A standard 10mm ply seat form was cut out and the back of the seat was sprayed in car underbody paint to keep out the water. Tee nuts were fitted before the seat was covered by new 1” firm foam and a cream vinyl fabric that will compliment and contrast the red and black of the main trike frame. A set of “LOCUST” decals were cut and ready to install after the trike is painted, along with a set of
mudguard mounts and front lamp holders that will mount on the inside of the front wheel tabs.
Ready for paint and decals
After several miles in an unpainted condition, I stripped down the Locust and primed and sprayed the main frame in Italian Racing Red with matt black ”trim”. That includes four coats of primer, five coats of colour and two coats of lacquer on the red parts.
Painting the black components
The matt black parts had couple of coats of primer and three coats of matt black. Then, the frames and other parts were left to stand for almost a week whilst they hardened prior to reassembly.
Painted with decals
The LOCUST, Atomic Zombie and Made in England decals were fitted after 24 hours and the adhesive normally achieves maximum strength in 24 hours, long before we needed to handle the frame and other parts for assembly.
Assembled Locust Trike
With the painted parts hardened, the trike was re-assembled and the plastic end plugs refitted. The gears and brakes were checked over and cable ends fitted to all the cables for a professional finishing touch and ready for the finished photo shoot.
The Completed Locust Tadpole Trike
The conclusion to the project is yes, a trike can be built using second hand tubing. But, when factoring in the extra effort needed and the extra time, there really is little difference between using salvaged tubing vs. new tubing to build the frame.
I have found that 40 mm 16g ERW square tube is a lot easier to build with; however, the round and oval tubing does give the trike more professional look. This trike has since been passed on to a new (disabled) owner so that he can get some exercise in the open air.
More of Emma's Low Cost Locust Tadpole Trike project
can be found @ the Atomic Zombie bike building forum. Many thanks to Emma for sharing her story and pictures and for promoting our family friendly bike building community.
If you'd like to order decals, please contact Emma directly on our Builder's Forum.