Cabling a BMX track for transponders

Timing positions.

The Transponder system uses at least 3 timing positions around the track.

1. Gate drop.
2. Bottom of the Start Hill.
3. Finish line.
4. Intermediate loops. (optional)

The Gate Drop is picked up with a cable run from the Start Controller (SmartStart, ProGate or similar) to the first Decoder (normally named Hill Decoder).  An Interface box is needed between the Start Controller and Decoder.  See further in this document for details.

The Hill Loop is put at the bottom of the Start hill.  Normally about 10 to 20m from the gate.  But this measurement is not critical and basically goes wherever suits.  It does need to be at a point where riders would normally cross the loop between 1 & 10 seconds after the gate drop.

The Finish loop is also two parallel conduits run across the track.  The first conduit is buried 600mm before the finish and the second conduit is under the finish line.  The finish is when the transponder is exactly in the middle of these two conduits.  With the transponder mounted on the fork this puts the front wheel just touching the finish.  Install them as per the instructions below.

Intermediate Loops.  Extra timing loops can be added at various positions around the track.  These loops give split times around the track.  Uses for these intermediates are for coaching sessions and for commentary to assist the announcers identify the riders and positions.

Further in this document is the recommended method of installing the loops in the track.

Mylaps instructions for positioning the loops are:

Finish loop placement.

Mylaps advises the conduits are 100mm deep but I prefer them shallower.  Basically have them deep enough that they are not going to be in the road when doing track maintenance.  Another idea is if you have a concrete start hill and no suitable area after the concrete is to simply run two cuts in the concrete across the track 600mm apart.  Then simply lay the cable into the cuts and hold it in place with some silicone. 

Decoder Cabling.

The Decoders are normally in the scoring hut.  Cables are required from the decoders to the timing positions.  The cables from the Hill and Finish loops are coax type cables; MyLaps coax is recommended for 2 reasons:

• it connects directly to the loop without a BNC connector (bad BNC connections can be a source of timing issues)
• using MyLaps coax means you will have MyLaps equipment from the loop all the way to the decoders

Start Pulse Cable

The start pulse cable is run from the Hill Decoder to the start controller.  Any 2 wire insulated cable can be used.  If purchasing cable any insulated cable with at least 2 wires is suitable, telephone cable with twisted pairs is excellent.  It can be buried or overhead cabled, it should be in conduit to protect it.  If the Start Hill has a roof it can be run along the roof to reach the start controller.  No connectors are required on this cable.  This cable connects directly to the Grey Interface box.

Cables from Mylaps.

Track cabling supplied from Mylaps comes in the following lengths:

Detection loops

• ProChip detection loop 6m
• ProChip detection loop 9m
• ProChip detection loop 12m

Coax

• 20m and connector box
• 50m and connector box
• 100m and connector box

Most tracks will use a 12m loop at the Hill loop and 9m at the finish loop.  But measure the track width at these points to determine which length loop will suit.  Secondly measure the distance from the loop to the registration hut. 

How to install track cabling.

Below is photos of how to physically install the conduits and cabling at the track.

This method of installing conduits was developed by Neil Cameron from BMX NSW.  This method means that the cabling is sealed and not visible and should be very reliable.

Start/Finish Loops

Many clubs already have conduit in the ground through their tracks. The size of that conduit will determine what elbows, t-pieces and inspection points you use. The following pictures have all been made out of 25mm pipe, which is enough for the loop etc, but if you have bigger pipe in the ground then you can step it down with reducers to use 25mm elbows etc, or you can just use elbows and inspection points out of the size you have already.

The following photos shows what the system looks like buried in the ground. Obviously I have shortened the pipes in the track (where you can see the coils of white wire, and the pipe between the T-junction and the box should be much shorter, so that the box is right next to the track.

Position of the elbows and pipes in the track

The elbows (ends of the loop) need to be 50cm past the white line on the track. Therefore you need to know where the sides of your track are, and where they will always be. This may require measurement from a fixed point at the venue so you can always tell where the ends of the loops are.

This also means you need to know “exactly” where the finish line is, and where it will always be. So measurements from the jumps on the track for instance are not accurate, and will change over time. So you need to measure from something at your venue that will not move (like a drain grate, or power pole etc). You will need exact drawings because the white finish line needs to be in a very specific place and over time this buried system will be forgotten.

Finish line position

The white line marked on the track goes on the last pipe in the ground. So when travelling down the finish straight, you will pass over the first pipe in the ground, then 60cm later you will pass over the second or last pipe in the ground. The white line must go directly over the last pipe.

For this reason you need to put something in the ground beside the track to mark the finish line, or have a way of measuring exactly where that pipe is as you will need to remark it both during a race day and once or twice a year when using the finish line.

It is also very important to know where the sides of the loops are, so that you can paint your white lines in the right place each time. We can’t have the track change from year to year and move away from the correct positioning of the pipes.

If we turn up to a track and can’t work out exactly where the finish line is, someone will be taking a shovel to your track and digging to find the second pipe 

Start Straight loop position

This doesn’t matter. The start straight loop can be anywhere near the bottom of the start hill. There is no specific measurement for this. So put it 1-2 metres past the bottom of your concrete/tar of your start hill. It’s a good idea to keep track of the exact distance just so you know where it is when digging your track at a future date. You will also need to know where the sides are. Over time tracks get wider or narrower based on dirt work by different people, and without marking on the start hill, or some measurement, you may well end up with the track running outside your loops in the future.