The View Up Here

Random scribblings about kites, photography, machining, and anything else

New KAP Ground Station

Posted by Tom Benedict on 27/05/2013

Earlier I mentioned I’d picked up a 7″ Feelworld LCD monitor to rebuild my KAP video downlink. I finally got around to building the ground station to go around it.

KAP Video Ground Station

The heart of it is that 7″ Feelworld LCD. These are meant for wireless video, so they don’t switch to blue screen when the signal glitches, or assume the signal format has changed, and try to automatically re-negotiate PAL vs. NTSC. Those settings are manually done, and if you get static in your signal, you get static on your screen.

The larger size is also easy to see without wearing my glasses. I’m far-sighted, and old enough now that my near vision requires me to use glasses to read. Even using my phone without glasses can be troublesome. My older monitor was nice and compact, but difficult to see without putting on glasses. Unfortunately, once I put them on everything beyond about thirty feet goes blurry. This means I can’t see my kite with my glasses on, and couldn’t read that tiny monitor with them off. But the larger screen on this monitor is easy for me to see, with or without glasses. Problem solved.

I wanted the whole ground unit to be a single compact brick I could mount to my KAP transmitter, stick on a tripod, hand to someone, etc. It required some modifications, but they worked out well.

KAP Video Ground Station Rear

The monitor had a 75mm VESA mount on the back, to allow it to be used with VESA accessories. I made a backer plate for the monitor to house all the stuff I wanted to use with it, and popped four holes on 75mm centers so it could be bolted straight to the back of the monitor without modifying anything. The backer plate houses the 5.8GHz receiver – and doubles as a heat sink for it, and also contains the battery and the main power switch.

The battery is a 2.65mAh 3S LiPoly that was designed for use in an RC transmitter. It’s a 1C battery, so it can only source 2.65A. But the current draw on the monitor and video receiver are so low, I’m not even close to this value. It should provide plenty of juice for a full day of KAP, and charges in about 20 minutes.

I was on the fence about adding the power switch until I tried plugging in the battery and mounting it to my KAP transmitter. Bleah! Talk about awkward. The switch took less than half an hour to pop in, and makes it way more convenient to use.

KAP Video Ground Station Battery Compartment

The battery is held in place with nylon webbing stitched to industrial strength Velcro. The entire battery compartment is lined with fuzzy Velcro for cushioning, and the strap extends almost the entire length of the battery. Plenty of grip to keep things in place in the field. I added a finger tab at the end to make it easy to pull off to get the battery out for charging. (Never ever charge a LiPoly battery in the device!)

KAP Video Ground Station Bottom

In addition to the VESA mount, the monitor also included a 1/4″-20 threaded hole for mounting to a tripod, and a T-slot for mounting to some other rail system. The T-slot worked great on the mounting arm I’d already stuck on my KAP transmitter, so that’s the one I chose to use. But I left the 1/4″-20 socket exposed as well in case I want to mount it to a tripod for easy-chair KAP.

All in all the ground station has worked out great. The reception is far better than with the old system, and since the video doesn’t glitch every time there’s static in the signal, the usable range is huge – far larger than I really need for a KAP video downlink.

Which takes me to the other reason I wanted this to be a removable, stand-alone handheld system: It’s pretty trivial to get a second video transmitter and stick it in an RC airplane. Aaaaah! More fun!

– Tom

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One Response to “New KAP Ground Station”

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