KAP RC Tx Miniaturisation

Small is beautiful. Having got a working Arduino based remote control for the RC rig and successfully testing the manual/auto function a smaller, handier option is possible. Looking at the available cases I found options that are small enough and include a battery compartment fairly scarce, after far too much browsing I found this by Takachi:


This is the IP67 version of the Takachi series case. Part No: WH 145-20-F4-BY . The threaded fixings are steel to brass. It is supplied with a battery holder for 4x AAA batteries and has an internal space just big enough for the components required. On test the set ran for 4 and half hours on 4xAAA batteries. In that time the power supply had dropped from 4.99v to 3.56v. I don’t expect to maintain the IP spec, the tilt slider alone ruins the enclosure but starting with a tough case seems like a good idea.


Solder and wrap. With practice I was able to use a 14 x 20 hole matrix board to mount the Micro Pro, RF unit and DIP switch. I soldered a wire across the ‘on’ side pins of the DIP switch for the -ve contact and wrapped soldered tails from each pin to it’s control on the Micro Pro. The height inside the Takachi case meant the board had to be cut down and the RF unit placed separately to fit:

The rats nest of long tails lets the lid mounted stuff survive the fit -re-fit process and keeps access to the USB input for sketch updates. The case is heavy duty ABS which makes cutting holes in it a bit of a fiddle. A wood drill whistles through it but a swiss file clogs horribly, a high speed tool like a Dremel melts it with a disgusting smell.

Working single handed, thumb operation of the shutter and tilt is positive without loss of grip on the case. The power, pan and auto switches are mounted top-down ‘though hole’. The Gteng video Rx just fits above the shutter button. A stub antenna makes the unit balance in the hand. Range test proved this is as neat as it looks.

Takachi provide a sealed space for the lanyard below the battery compartment, fitting a salvaged Spektrum eye bolt proved difficult so the all important neck loop is tied off inside without a swivel.

Servo trouble. Somehow or other I couldn’t get the Feetech fsr90 ‘micro’ continuous rotation servos to behave under Arduino control. I could centre them for manual but they would just stall under auto. This needs investigation as the addition of a Parallax servo has added weight to the rig:

Desperate hacking got the oversize gears and servo to fit and I had full L/R pan control and auto pan stepping. Days of cloud passed and eventually I got sun and wind. I took a chance and hoped the auto would pay off in marginal lift. The little Tx was stuffed in a jacket pocket when it took this shot …

…whilst I was hauling line in lull. It is a complete surprise and all the more so as I had the Tx stuffed in my pocket at the time. The surprise element of autoKAP is sometimes it’s own reward.

Tx evolution. It’s been something of a challenge but getting the Arduino controller down to pocket size saves a huge amount of space in my luggage and adding the power of automation seals the deal for me: without major modificaton to the RC rig I have optimised control.

About billboyheritagesurvey

Heritage worker
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