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Some basic building tips
Here you'll find some basic tips and information about building a Rorty. It'll give you an idea of what to expect on your buggy building journey. Don't forget there is plenty of support available as well as prefabricated kits and you can also Build@Rorty!
With the plans pinned to a board in the workshop, it's time to prepare a chassis stand, and fabricate the jigs for the A-arms and trailing arms. If you have plenty of space in your shed, the ideal chassis stand has a permanently positioned, perfectly levelled, horizontal steel plate, at least the size of the buggy. Of course you'll find the plans to build your own table suitable for your Rorty in the buggy manuals. Various bits and pieces can be tack welded to the table to support the chassis/suspension as it's being built. These "third hands" and "sky hooks" can be ground off flush again afterwards.
If on the other hand you are restricted for space, a moveable stand with adjustable feet is the answer. The tables have many uses and the top can be replaced for each project. For a budget portable table it consists of a sheet of 19mm (.75") MDF, on which about five equally spaced lines are marked along its length, and at least five across its width. If this grid is square, then your buggy will be too. All these instructions are repeated in the manuals so don't panic!
The centre line in the long axis is used to set out the various chassis width measurements, and two of the lines across the width of the table should represent the wheelbase. All the other lines merely act as reference and sighting lines. Every stage of the way, sight through the chassis to these lines. Your eyes will pick up any distortion, or measuring mistakes.
Making jigs for A-arms, trailing arms, or any removable parts is essential, and must be done with the utmost accuracy. We have designed the suspension jigs so they will make arms that can be mirrored from one side of the buggy to the other.
Shock mounts etc are added with bolt on jigs to "hand" the arms. In addition to plans provided for essential jigs you can even make a jig to attach the arm mounting tabs accurately to the chassis. If you ever tear an arm off in a race, or on a rock, simply place a few lengths of tube in the appropriate jig, and weld up a new one that will exactly match the old one, and moreover, fit the chassis perfectly!
Mounts and Tabs
Time to start making things. We recommend making all the engine mounts, arm mounts, and dozens of other chassis tabs before touching any round tube. Carefully mark and cut them from RHS tube, to suit any bushes they have to locate. Alternatively, you can purchase them from us or there are a number of specialist companies manufacturing tabs.
The materials commonly used in mini buggy chassis are Ø31.8mm x 2.1mm [1.25" x .083"] CDS/CDW/1020 DOM for the main structure. Elsewhere, 31.8mm x 1.6mm [1.25" x .065"], 25.4mm x 2.1mm [1.0" x .083"] (top A-arms), 25.4mm x 1.6mm [1.0" x .065"], 19.05mm x 1.6mm [.75" x .065"], 16mm x 1.6mm [.625" x .065"], and 12.7mm x 1.6mm [.50" x ,065"]. Material types are all specified on the plans so don't be overwhelmed by the available choices!. If you have trouble sourcing DOM as specified, we use CDW tube for diameters above 19mm or otherwise the cheaper ERW tube (with the weld seam up the inside) for items in either compression or tension.
The CDW tube is commonly 470 MPa, is relatively elastic, and easy to weld with a MIG. We use 4130 chrome moly tube for the lower A-arms and trailing arms, because of the punishment they take. CroMo is typically around 650 MPa, and should only be TIG welded, but should then be heat-treated to normalize the metal again. There are many opinions of the requirements for post weld heat treatment. Do some educated research and make your choice. Steel suppliers are generally very good sources of information.
Chrome moly tube isn't any lighter than mild steel tube, but it does resist deformation far better than mild steel and can therefore be used in thinner sections resulting in lighter overall components.
Building, Bends and Welding
Don't try and build the entire chassis out of just two tubes. Work out the joints, so the length of a tube, and number of bends in it, are kept to manageable limits. The manuals and plans explain all this in detail to make it as easy as possible for you to build your Rorty in the home workshop. We even sell the plans for you to make your own benders and notchers along with heaps of other useful professional quality workshop tools!
Draw full size profiles of the tubes on another sheet of MDF, and glue neat wooden blocks at intervals along the outline. Then simply bend the tube, and test fit it to the profile board.
Allow enough material at each end of the tube for cutting the fishmouth. Again, read the centre of the fish mouth off the profile board. Cut the fishmouths with a tube notcher. Accuracy here is paramount. It's no use cutting a rough end on a tube, which doesn't butt up nicely to the major tube, and telling yourself you'll fill the gap with the welder later on. Unless the fishmouth mates with the major tube all the way around, the shrinkage in a large bead of weld will "pull" a non-mating fishmouth, and distort the chassis.
And you thought this was going to be difficult!
Avoid the temptation to rush the job and finish all the welds. We recommend just tacking the entire buggy together, and assembling absolutely every last item including throttle cable, wiring loom, seat belts etc. Only then can you be 100% sure that after painting it and assembling it (for the second time), you'll be able to take it straight out and race it without any modifications.
Sounds like a lot of extra work but experience tells us you'll be glad you did! There are a few beautifully finished chassis that are lying in the scrap pile at the back of some people's sheds, never to see a racetrack simply because they were impatient and hadn't fully planned the build!