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Perfex KT-18 Modifications

Posted 01-16-2010 at 12:37 AM by color0
Updated 03-08-2011 at 09:31 AM by color0
Although many of us Mini-Z Racers have high-end KO, Airtronics, and Futaba radios for our Mini-Z's to use, I'm sure that there are just as many out there who read this blog who have just gotten started with Mini-Z -- which means that you very likely have a Perfex KT-18 in your posession.

The KT-18 is not a bad radio: it's 2.4GHz ASF, has throttle and steering trims and EPA's, and even has a "training mode" that you can use to save battery power or test run a new track layout. But it does have several disadvantages in the hardware that we can correct or at least alleviate.

#1: Fairy-light steering wheel tension. The stock KT-18's steering wheel has so little tension it's really hard to tell where center is. Here's the fix:

Stock, the steering tension is controlled by a very weak pull-spring mounted on the mechanism shown above. As you can see, you can replace said spring with a number of small rubber bands. You can get these from your dentist, probably for free. Anyways, the bands increase steering tension to an appropriate level, making the KT-18 steering just "feel" so much better in your right hand.

#2: Crappy steering wheel grip. The stock grip that comes with the KT-18 wheel is slippery, plastic crap. It also makes the entire wheel way too large for my hands. So what you can do is replace that plastic with wheel foam for a high-end radio, or, do what I did and wrap some used Mini-Z tires around the rim.

Four worn-down PN 6 radials will do the trick just fine.

#3: Too much steering wheel travel. This one may not be for everyone, but I thought that the KT-18's steering wheel travel went way beyond the mobility of my wrist. Hence, I adhered some squares of foam to the plastic limiters on the radio's casing, reducing travel by a few degrees each way.

You'll have to readjust the trims to get the same amount of steering lock from your car after you do this mod, but for me at least, the reduced travel made steering a much easier proposition.

#4: Low voltage. (NOTE: This one will void your warranty for sure) The KT-18 is designed to run on 4.8V, which is all fine and good if you're playing Mini-Z on your own. But unfortunately, almost all other radios it'll be competing with at the track (KO, Airtronics, Futaba, etc.) are running at least 9.6V through their circuitry, with the result being that the KT-18 gets drowned out. I've been witness to this phenomenon several times before deciding to up the voltage on my KT-18.

What you see here is the stock KT-18 battery tray re-wired for use as a 2S2P lithium-ion battery tray. The procedure is only a little tricky: 1) Remove from the tray the battery contacts on the right side of the picture. 2) Cut it into three pieces, left side, right side, and a thin strip that should be left in between. 3) Throw away the thin strip. 4) Reinstall the now-split-up battery contacts into the tray. 5) Solder some new wires in an X-pattern across the contacts, making sure that nothing will short once you have the battery contacts in (look very carefully at the picture). 6) Pop four AAA lithium-ion cells into the battery tray in the same orientation you would with AAA NiMH cells. 7) Check with a multimeter that the battery tray now reads in the 8.4V range (with fresh lithium-ion cells).

The added voltage definitely helps the KT-18's signal get across the track more effectively, but do note that sometimes, problems with the throttle range will arise. For some KT-18's applying full throttle can make the car lose throttle completely, while applying 99% full throttle becomes full throttle at the car. Just shim the backside of the trigger until you're not losing power at "full throttle" anymore, and you'll be good to go.

So there you have it, four relatively easy modifications you can do to your KT-18 to customize its feel or performance for your requirements. If you have a KT-18 now, this article will probably help you hold on to it for just a bit longer before the rest of the Mini-Z bug bites, and you splurge for a module-based high-end radio for your addiction.
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