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The ‘TvB’ Flexible Guide-Flag Arm Chassis

By Peter Timothy van Buuren - March 9, 2000

Plan view not to scale.
Length 120mm - Width 70mm
Chassis box same width as motor and 60mm long

This is a chassis I have designed and built in 1/32 scale using Scalextrics parts and PVC from a 2mm thick 75mm diameter drain pipe about 300mm long. The diameter is not that important. When looking for PVC make sure it is not the sort that feels soft and is easy to scratch with your fingernail as it is not PVC and will not take the sort of adhesives that are to be used. The PVC pipe is cut up the middle like cleaning a fish, heated until pliable, then sandwiched between two pieces of glass or smooth board. I have used a woodworking hand plane to straighten the edges and square them, but a craft-knife and straight edge work as well but take longer.

Cut 2 strips 10mm wide the length of the sheet and file or sand off the burs on the edges.

On graph paper using a ruler and pencil, draw the plan of the main part of the chassis (the box section is the same width as the motor and its length allows for both the motor and rear end) with a separate drawing for the side wing like structures. Place the drawing on some smooth board (no need to glue) and using 3mm thick nails with the heads removed hammer them into the inside of each corner of the drawing allowing for the thickness of the PVC.

For the guide-flag hole put a pin the appropriate diameter. I use 1/24 scale guide-flags as they are easy to fit and wire up. This is the jig for bending the strip of PVC. Heat one end of a strip and bend it round the flag pin so that it overlaps itself 10mm. Use a pair of pliers to squeeze the strip together. When it has cooled, lift it off the pin and check to see that the flag fits well and not sloppy. If the flag does not fit the way, it should, reheat the strip and try again.

The joint where the strip meets itself is cleaned with solvent and glued with Cyanoacrylate adhesive (superglue) which bonds very well (use eye protection). Refit the strip to the jig, pencil where the next bend is, remove from the jig, heat at this point, then fit back to the jig and complete the bend. Work around the jig in this manner until you are back to where you started and overlap 10mm and having cut off the excess strip, glue as you did for the guide-flag hole. I have heated and bent this frame on the jig but used gloves for protection. The PVC is very forgiving when it comes to bending around the tight corners of the jig, and reheating to straighten or adjust, so relax and enjoy yourself. Use a steel rule to aid in straightening the softened PVC.

Complete the wing structures the same way using the second strip and set them aside for now. Remove the gear from the rear axle and refit the back wheels. Using the off-cuts cut two pieces 15mm long. Clean the parts and glue one piece each on the outside of the frame where the axle will pass through allowing clearance for the crown gear when placing them. Each piece having its end level with the bottom of the chassis and extending above the top of the chassis.

The parts can be cut oversize and trimmed later. With the guide-flag (with its braids) in place set the chassis up at the correct track to chassis clearance using a smooth board with a slot cut for the guide-flag. Mark the board with grid lines in alignment with the slot. Mark where the axle holes will go using the rear end with wheels and tires in place but no gear. Allow for the gear clearance. Use the grid on the slotted board to aid marking accuracy. Do not worry if its not exact that is taken care of in the next step.

Drill a 6mm hole through both sides using a slow speed. Clean the area of the axle holes with solvent ready for glue (not a lot of solvent, just a wipe). Take one wheel off the axle and wipe the axle with motor oil or a molding release if you have it and place the axle in the chassis being careful not to touch the chassis with the axle and its light coating of oil etc. then replace the wheel. Mask the wheels to avoid glue.

Using a strong, (24hr) two part gel type epoxy glue press glue in and around the axle holes allowing it to ooze and expand around and wider then the axle holes. The mess can be cleaned up after the glue has had sufficient time to harden. Now check that the axle is proper alignment using the grid-lines on the board, and that the chassis has proper track clearance. Set aside to harden.

After hardening has occurred, remove the wheels and twist loose the axle using the smooth part of your long nose pliers so as not to mar the axle. There will be an audible click when the axle releases. If the axle resists try using a soldering iron on the axle ends to expand the metal a little then let it cool and try again (not hot). Remove the axle and clean up excess glue but allowing for some to stay wider than the axle holes as the epoxy does not adhere that well to PVC but more than strong enough for this project. Another much heavier model that I have made with these bearings has lasted for many months and many crashes without damage or wear. Use a synthetic lube like ‘silicone’.

Pass a 3/32 drill through the holes by hand then test that the axle spins freely. If the axle is a tight fit it will get warm, expand and slow the car down as well as heat up the motor. Fit the axle, its gear, and both wheels in the chassis with the guide-flag. Put the assembly onto the slotted board.

Wipe clean the motor-can and its position in the chassis with solvent. Using construction type contact adhesive (liquid nails) smear some adhesive on the motor-can and in the chassis then place the motor in the chassis and line up the gearing. Check track clearance and allow to dry. The motor can be wired and run to check gear alignment and adjusted before the glue gets really firm. New motors can be fitted by cutting the adhesive with a craft-knife. The wing structures are used to mount the body and are fitted and glued with Cyanoacrylate adhesive allowing for clearances then trimmed and tapered to use as skids.

Trim the top of the guide-flag arm so it is tapered towards the front from 10mm to 6mm to allow the arm to flex so as to take the shock out of cornering as it was designed to do. Experiment with it. As can be seen this is a light chassis but quite strong and allows for easy repair if needed. I have crashed mine a lot and have only broken the wings of once each at the joint. They glued back easily.

The body used is made out of the clear top of a shirt-box and held on with tape. My son enjoyed decorating the body. I’m sure this design could easily be adapted to other scales using up-sized materials. Try it out and tell me what you think.

Notes from Slot Car Garage: You can email Tim at vanbuuren@picknowl.com.au with any comments or questions. We wish to thank Tim for sharing this chassis design and instructions with us.

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