Looking for help understanding the wiring in my steadicam

[bob'slaststand]

I bought an old steadicam by Floatcam. It was really cheap and I know their kit from their jib/sliders and it’s always well made so I was curious. When it arrived I was amazed at how well put together the thing was, made my Steadicam Flyer look cheap and flimsy. So I set about doing it up.

It has a 2 pin Lemo for power and a BNC for video on the stage. The bottom has a cross bar with a battery mount on one side and a monitor mount on the other. All the wiring is internal with a 2 pin Lemo on the battery side that the battery plate plugs into and a 4 pin Lemo on the other side for the monitor.

It came with a standard definition monitor with one cable coming out ending in a 4 pin Lemo for both power and video signal.

Now the monitor was broken and I needed to upgrade it to SDI anyhow so I removed the cable from the broken monitor but was surprised to find only 3 wires inside. One red, one white and one running in the sheath.

I contacted Floatcam and they told me that the white wire was video the red DC positive and the video and Power shared the negative/ground in the sheath.

I made up some cables just with connecting blocks to test everything before putting the cables together permanently. I built a V-mount battery plate for the power and plugged it in the 2 pin Lemo end of the bottom bracket. I checked the 2 pin Lemo in the stage and it was live, 15V. I checked the red positive and sheath negative wires in the monitor cable and there too 15V, all was working as it should with the correct polarities.

So I wired up a temporary video cable splitting of the monitor cable with the white to the BNC pin, the negative to the BNC barrel and the red, the DC positive, I left unconnected as both the camera and the monitor were running of their own batteries and the monitor was 12V. I just wanted to see if there was a video signal.

This is where it goes terribly wrong. I plugged the SDI from the camera into the BNC in the stage and plugged the BNC from the monitor cable into my monitor and it fried the SDI unit on the back of the monitor.

I was confused, how could the video signal from a battery powered camera fry my monitor SDI in. So I checked the voltage coming out of the white video wire in the monitor cable and it was 15V! I unplugged the camera and checked again, still 15V. I checked the red cable and it was 15V too?

I was a bit confused about how the video would work in this set up. I presumed that the white video cable just ran from the BNC on the stage to the monitor but now I see there must be somewhere in the steadicam that the battery positive is connected to it.

I’m not too good with electronics and I’m trying to lean as I go along, dose it make sense that the current from the battery plate would be coming down the video feed? Was it simply that 15V was too much, if it had been 12V would the SDI in be fine? Do video feeds normally carry high voltage like that?

I’m really confused and not sure what to do next. I am hoping someone on here who knows more about this kind of thing would read this and help me out with some explanation.

 

[CharlesPapert]

I can't tell you exactly why or how voltage made it to your white wire, but a video signal shouldn't have voltage running on it for this kind of application. It was fairly common to have common ground between video and power even for pro-level Steadicams, but that was in the standard def days.

However, even with that sorted out, you need to have a dedicated line for SDI running through the rig. SDI won't travel across standard Lemo pins the way composite video did. If the rig allows for it, run a quality BNC down the post for SDI video. If not, the best way to manage it is to run the cable from the front of the top stage straight to the monitor. It shouldn't affect operation (you'd have to pan more than 90 degrees towards the arm before it would start to become a nuisance, which is normally not done anyway) but you would have to remove it for spin balancing.

As far as Floatcam making your Flyer look flimsy...well...the Flyer wasn't a great sled by any means, but the arm was definitely superior to any of the cheapo rigs that followed. I ended up modifying one of those arms to work with my little "running rig" that got a lot of use in the early DSLR days. Also, when the Flyer first came out I took one over to the set of "Inland Empire" which David Lynch was shooting on DV to give him a demo. He ended up inviting me to do a shot which ended up in the film, which was a bit of a surprise!

 

[bob'slaststand]

Lynch must be such a character, I came across his book “Catching the big fish” about how he has ideas using transcendental meditation and all that lark, it’s crazy read.

I know it’s unfair on the Flyer. I guess the kind of cameras that were in its weight range when it came out meant it didn’t get the love that Steadicams in that weight bracket get now. I can’t forgive that 3/16 bolt and pinch joint for the battery plate but the arm as you say is a good one. I was more complimenting the Floatcam than digging into the Steadicam. I think it’s the Aero these days and it looks like a well built bit of kit as you’d expect.

I’m pleased to hear that you’re as confused buy the battery DC coming down both the power and the video cable, I think? I’ll write to them and see if I can get this cleared up. I’m sure I tested the old monitor without the battery plate attached, just feeding a SD signal into the BNC on the stage and plugging in the monitor. I don’t know how digital cables works but I presumed you had to make a closed circuit, it is still electricity after all so how can a current come from one power source and end in another one, one that’s not connected to the same place if connected at all?

I called Lemo about the socket before I tried this and though it’s not within specs nether is the SD cabling and I have always found that a HD SDI signal runs the length of SD wiring in an old steadicam with no bother. Saving the need to replace the video cabling inside. It’s just too short a distance for it to be an issue and I was hoping that the same might be true for the Lemo, the guy there said you can give it a go, maybe it’ll work but it’s outside the parameters of the connection. So thats what the tests were about when I killed my most prised and only SDI monitor.

The issue with this Floatcam is, and I’m a bit embarrassed about this, I can’t see how to take the damn thing apart. The bottom bracket is a solid aluminium bar with the Lemos mounted on ether end but the crazy thing is that there is no join. This rod must have been machined out from the middle and then the Lemos somehow installed and I don’t fancy trying to remove or, god forbid, replace them. They must have made up some kind of tool to install the things.



That and the fact they soak every last nut and bolt in as much Locktight as they can get in the holes before putting it together made me really want to test to see if I could get it working with the current wiring and sockets. It does not look promising though. Looks like I might have to have another go at dismantling it. I could run a new SDI cable through as you say and just have the power and SDI hanging out the hole left behind by the removed 4 pin Lemo. Which I’ll probably have to cut off. Sticking a ball of Sugru in the hole to make it water tight. Such a shame though, I really wanted to use the sockets in place, nice and neat.

 

[CharlesPapert]

Have you checked continuity on all the wires to see if there are unexpected crossovers? Since you mentioned the voltages, I'm assuming you have a voltmeter so it should have a continuity setting.

Is that not a cap on the end of the section in the picture? It looks like there is a seam just after the lemo connector.

One other approach to take may be to drill a small hole in the top and bottom of the post and feed cable through, then crimp BNC's onto the end. Not the easiest as it will fight with the existing cable on the way up, but you might be able to fish it through! Make sure to use 75 ohm cable (vs 50 ohm).

I'm surprised you have been able to run SDI down an SD setup in other rigs if there were Lemo cables involved. When HD came in, everyone with an SD sled had to change out the cables and connectors (the manufacturers of the pro rigs which had quick release bayonets top and bottom had to spec custom multipin Lemos that incorporate mini-BNC mounts nestled in with standard pins), I don't recall anyone finding themselves "lucky". Is it possible that the sled you got to work didn't have Lemos, that the BNC's at either end had their own dedicated cable? That would most often be the case with sleds that simply had video and power running through them, it would be simpler to have two internal cables than one that ran both like the Floatcam.

 

[bob'slaststand]

I can check continuity but as there is 15V coming out of the video I know the answer is going to be yes, the question is whether it is intentionally wired up that way for some reason. I can’t see how it would happen otherwise, maybe a failure at the pins inside the Lemo socket but it was working fine when I checked it with the original monitor and it’s not been used since then. It’s a good strong current to, I think it’s wired up like that. When I opened the monitor up there was some crazy wiring inside with lots of bits of tape, looked like someone’s DIY job. It’s the one that came with the steadicam originally I checked so I can’t think who would of been in there and what they could of been up to but it’s wired as I did with the shared negative and that power/video going to the same place.






I exactly what I thought before I inspected it closely. It’s not, on closer inspection it may of been a weld at some point but I don’t think so.

If it’s new cables I’ll strip it down as far as I can, cut off the Lemo for the monitor and replace the video with an SDI. It’ll be a bugger but I’m sure it’s possible.

No I never got a SDI signal through a Lemo just meant through the cabling that was used for SD video, saved me changing the wiring in the steadicam. I just needed to put new plugs and sockets on ether end. This was the first time I was trying to get it to run through one of these older Lemo sockets and it sounds from your experience like was unlikely to work anyhow. That’s why I was testing to see if I could get away with it.

I’m kicking myself over the monitor, I should have checked the video to be sure. I've hidden out of sight and am just trying to get on with something else and not think about it.