Had this response from Rob Nelson about the problems we found...
Hi Scott,
Thanks for the email. Graham has experienced what many carbon/aluminium chassis car owners have been frustrated by. Its not just an issue in RC but also full size vehicles to a lesser extent.
Very interesting and thorough analysis and a very good explanation of why carbon/aluminium is a problem.
Its not just aluminium but any conductive metal but aluminium tends to be the metal used for RC chassis.
The system uses what Mylaps call "Magnetic Induction" which is exactly what Graham deduced. The issue of carbon and aluminium is well know and is highlighted in the instruction sheet that comes with the Mylaps (and I think the older AMB) transponder. With carbon and aluminium chassis I recommend mounting above the chassis and at the edge, with some cars the steering servo is available in a suitable place. Bumper mountings also work if some distance from carbon/aluminium can be achieved. It would be helpful if the car manufacturers could take this into consideration.
My simple explanation is that the transponder is like a light that shines on the loop. Carbon and aluminium won't let the light through but other material (plastic, fiberglass) do. The light needs to illuminate the loop for as long as possible (hits) and needs to be as bright as possible (strength). Sometimes height helps with the faster cars to increase hits. The RC3/4 Decoder is very sensitive so signal strength is not such a big issue. Mylaps say strength >100 and hits >10 at speed should be OK. If there is noise then strength needs to be at least 60 above the noise.
One of the issues of side mounting is that if the cars tend to be at one side of the track as they cross the loop if the transponder is on the "wrong" side the signal can be compromised.
The difference in the signal for MRT is because they are reproducing the signal recorded from a "genuine" transponder.
If might be worth highlighting these findings. People are far more likely to read something on your website than in the sheet that comes with the transponder or I post on my website!
Thanks to Rob for this reply and I hope this helps others...
