Trailer for Vespa Scooter

I enjoy my Vespa (GTS250ie) a lot, I use it both for professional transportation, as well as for personal use.
Downtown, traffic is often congested, parking is always expensive or problematic, and the Vespa is a very effective solution to both.
On holiday trips, I started to realize it is actually one of the best vehicles to discover the world :
* riding on a motorcycle (or bike) allows to experience the landscape and scenery in a more intense way (compared to car, bus, train,..)
* it's speed is slow enough to be able to experience everything, yet fast enough to make some progress through the day
* it's not too expensive

The only disadvantage or problem is that you can't really take a lot of luggage with you : there is a small rack at the back, but it only accomodates a small bag. In front of the driver is a hook, which will hold a small rucksack.
I really needed more storage, either for equipment on profesisonal jobs, or for camping gear during the holidays.
After seeing some examples of single-wheel trailers for bikes and scooters, I decided to make a multipurpose-trailer for my Vespa

Given the complexity of this project, and the safety (and road-legal) requirements, this was going to be a project which would take several months. Your needs and capabilities are likely to be different, and so you probably won't be able to build one yourself simply following this instructable. Still I hope that this story may help and inspire you to build one, some day.

Good luck & Hope to meet you on one of my trips one day !

Requirements

1. Meet legal requirements. They differ from country to country. Google is your friend, as well as the forums of local scooter or motorcycle clubs
2. Safety : strong construction for worry free rides.
3. Durable : must withstand Europe's roads and weather conditions.
4. Payload : >100 liter of volume, and about 40 kg of weight. Legally, the trailer has a maximum weight of 50% of the vehicle towed by (150kg), so that means a total weight of max 75 kg. This led to the option of building it in Aluminum.
5. Comfortable ride : should not limit maneuverability of the Vespa itself. Ideally it should feel as if there was no trailer being towed/
6. No permanent modifications made to the scooter. (in case I want to sell it some day.)

Parts list

1. 12" wheel : I managed to buy one on ebay for 25 euro
2. Faes Cases Defender Aluminium Case. I used a FA-74 type of 990mm*450mm*380mm (162 liter of volume)
3. Aluminium tubes : 40mm*20mm*3mm
   1. 2 * 1050 mm
   2. 2 * 400 mm
   3. 2 * 360 mm
   4. 2 * 150 mm
   5. 2 * 380 mm
   6. 1 * 220 mm
   7. 2 * 255 mm
4. Plywood : 980 mm * 440 mm * 12mm
5. 2 x 4-function light block (rear light, braking light, turn indicator, license plate light)
6. 3" caster.
7. 2nd license plate

Tools
I can't be 100% exhaustive on the list of tools, but here are the most important ones

• Tape-measure, Caliper
• Steel carpenter's square
• Disc grinder
• Drill press
• AC TIG Welder

Costs : total 500 euro = 650 $

• Case : 300 euro
• Aluminium tubes : 70 euro
• Argon (TIG Welding gas consumed) : 20 euro
• Plywood : 5 euro
• Lights : 40 euro
• Caster : 15 euro
• Wheel (second hand - ebay) : 25 euro
• 2nd license plate : 25 euro

In order to get the dimensions right, and to solve several design challenges, I made a google sketchup 3D model.

I know Instructables.com is a fan of AutoCad, but hey, Sketchup is free and it does the job.

The frame consists of Aluminium tubes, welded together.
I decided to go with Aluminium for a number of reasons :

1. the case itself was also aluminium (and also the wheel had an aluminium rim)
2. it would reduce the weight of the trailer itself, yielding more useful payload
3. no extra protection agains corrosion is needed
4. it is a bit easier to handle than steel for cutting, grinding, drilling holes, etc.

But there are some drawbacks as well :

1. It is not as strong as steel (although strenght per weight is )
2. It is more difficult to weld than steel.

I didn't have any experience welding aluminium, but I had the right Welder, and I definitely wanted to learn to weld Aluminium.
So I decided this would be my first real Aluminium welding project. (I did practice on some leftover pieces first)
I also designed the trailer in such a way that if I made big mistakes in the frame, I could still make another one, and reuse all the other parts. The frame itself costs under 100 euro

The biggest challenge here was keeping all angles and lines straight : welding joints tend to shrink when cooling, and that often distorts the thing you're building. During preparation, I was extremely accurate about all parts. Still after welding not everything was perfectly straight or square. I need to improve my skills in this area. But the result (let's call it a prototype) was certainly good enough for real use. (the welds were strong, but not always as estetic...)

Lessons learned : Welding ALU needs practice, especially fillet welds are still hard. Thermal distortions are a real problem, so you need to design with that in mind !

The trailer coupling was another DIY challenge. As the trailer has only 1 wheel, it needs to rotate on 2 axes, but not on the third : no rotation along the length axis of your motorcycle.

At first I planned on using a Cardan coupling from a car's steering wheel transmission.
But after giving it some more sleep, I found a much simpler, cheaper and stronger solution : a caster wheel

What is important here is that a caster has nuts and bolts along its 2 axis, which are adjustable. This way by adjusting the nuts, the whole coupling can be adjusted to have absolutely no space or clearance along the third axis.

Furthermore, a caster has a nice base-plate allowing it to be easily connected to the rear rack of the scooter with only a few extra welds

I decided to make things a bit more compact, and drill new holes for the up-down axis. Then some unused metal could be cut away, making the piece a bit smaller, but same strength and functionality.

Lessons learned : when welding on the caster, decompose it to its pieces, then do the welding and reassemble.

I wanted to have the electrical cables for the lights inside the frame tubes. This is safer and cleaner.
You can't however have them there during the welding, as the heat of the welding proces will melt the insulation of the cable.
So I used a copper wire (leftover piece of 1.5mm2 solid core electrical wire) and pulled the final cable in once the frame welding was ready.

As for the connector, I thought the standard 7 pins connector was a bit bulky for a scooter, so I took a 5pin XLR connector and assigned lights as follows : 

1. Earth (or ground)
2. Rear light and license place light
3. Brake light
4. Turn indicator Left
5. Turn indicator Right

In Belgium, a trailer needs a separate license plate, and furthermore it needs one that is conform to very detailed legal specifications. So I ordered one from a shop that was certified to make replica license plates :http://www.nummerplaat.be/dyn/oude-nummerplaat
It was not that easy, as motorcycles have/had different kind of license plate, but only rarely need a 2nd copy for a trailer.

Lesson learned : weather-proof XLR connectors exist. I had better used one of those.

How does it drive ?

General driving : very smooth. On good road surfaces, you don't notice the trailer at all : No sounds, no bumps, vibrations at all. On bumpy roads, you will feel to some extent the bumps hit by the trailer. The center of gravity of the trailer is quite low, (in fact it is on a line from coupling to 3rd wheel) so the Scooter is not being pulled in any direction in turns.

Maneuverability :  The trailer is the same width as the scooter, so any gap the scooter manages to get through, the trailer will follow. Furthermore the turn radius isn't constrained by the trailer : it will happily follow the scooter when turning minimum radius curves

Load : until now I have loaded it with a maximum of ~ 30 kg. At this load, the handling was still perfect. However it is designed be loaded with 50kg. After having done more test-driving, I will load it with this maximum load and report back.

I will post a video one of the next days.

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Who knows, one day you'll build your own Vespa Trailer in TechShop Belgium :-)

Thanks for reading and Enjoy the ride !

Thanks to Guy (VespaShop.be), Marc (Aluminum), Dirk (Mentor), Ivek & friends (Mentors), Testas.be for their advice and support !