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Offroad Camera Project Revisited

Posted by Tom Benedict on 22/03/2013

I did some more work on the offroad camera platform I wrote about back in 2011. As delivered back then, the platform had a couple of serious weaknesses. First, having a highly compliant suspension meant that it never truly sat flat. So no matter where you drove, no matter what you took a picture of, your horizon was never, ever, going to be level. Second, the pan/tilt head from Servo City was inherently unbalanced, so the servos were constantly fighting the weight of the camera. In addition to burning through the batteries and making a pretty loud racket as the servos fought for position, this also meant that when power was removed, the camera slammed down either forward or backward onto its hard stops. Toss in a number of other minor annoyances like that bundle of cables on the side of the camera, and you can see it was far from ideal.

Crawler 1

So the 6WD camera platform came back for a mod job. Here’s the list:

Remove the Servo City tilt axis, replace with a tilt/roll unit:

The new unit is a variant of the HoVer KAP rig I made for my A650 years ago. In the case of my KAP rig, it was set up so the two extremes of motion on the servo gave me horizontal or vertical orientation for the camera. By flipping a switch on the transmitter, I could toggle between those two modes.

HoVer Axis

In the case of the offroad camera platform, the roll axis was centered on the horizontal position, with +/-45 degrees of motion to either side to level the horizon. The only real mechanical differences are that the tilt frame had to be a little wider to clear the video and shutter cable on the side of the camera, and I used a beefier arrangement for the roll axis using Servo Blocks from Servo City.

Servo Block Built

Unfortunately, when I put everything together I found that the Brooxes KAP gear was too flexible to work in this application. But let’s face it: In the world of KAP, having a slightly compliant rig is a bonus, not a detractor. And lightweight is the name of the game. So it actually works really well for what it’s designed for. But this thing is intended to roll over rough terrain and potentially get thrown around a lot. Rather than start over from scratch, I beefed up the main frame with corner bracing and a brace across the back to stiffen it. The tilt frame didn’t get any bracing, but if it looks like it’s necessary down the road, it’s easy enough to add.

Roll Axis

Replace UBEC voltage regulator:

In testing the changes to the camera mount, I ran across another problem: Occasionally the servos would jerk and shake, and sometimes while driving at full speed the motors would slam to a stop, then resume at full throttle a moment later. Scary! I wound up checking the servos, the speed controllers, and finally checked the voltage regulator I’d installed when the unit was first built. GAAAH! It was noisy! Time for new hardware.

A while back I converted the video system on my KAP rig to a 3S LiPo battery, but kept the 4xAAA battery pack for driving the RC receiver. On the advice of a fellow KAPer (hi, Bill!) I’ve been wanting to install a UBEC to power the radio instead. What a perfect opportunity! I ordered two 3A continuous / 5A burst UBECs from Hobby King, and when they arrived one went in my KAP rig and the other in the robot. The KAP rig worked perfectly first try (thanks again, Bill!) and the installation on the 6WD robot was a snap. Most of the noise went away. (Yeah… most… more on that in a sec.)

Replace the antenna support:

Back when I started on this, there was limited selection for radio and video gear. The only video link that fit the bill was a 2.4GHz system. This precluded using a 2.4GHz RC radio, so we went with a 75MHz ground radio from Hitec. I’d post a link, but it has since been discontinued. The one gotcha with dropping to a lower frequency is that the antenna gets longer. And for best reception it needs to be mounted well clear of the vehicle. The first rev used a fiberglass rod I mounted in a Delrin block to support the antenna. But it was hard to transport, was fragile, and finally snapped off at the base.

For this rev I looked to the RC car and truck world for inspiration. Not only did I find it, I found nice off the shelf components that fit the bill perfectly! Now the radio antenna is supported by a Dubro antenna tube that mounts in a nice machined aluminum collet system from Integy. It holds the antenna out of harm’s way and up in the air for good reception, and is easy to break down for transport. In the end I bought two: one for installation and one as a spare. But I wound up mounting both because it’s handy to have a second mount on the drive system for those times when the upper deck is removed for servicing.

Antenna Collet

Build a new video cable

As you can see in the photo from the original 2011 build, the cable from the camera to the video transmitter was the stock Canon A/V cable that came with the camera. “Ungainly” is a kind word to describe that bundle of wires. But with the addition of the roll axis to the camera head, “disaster” came a little closer to the mark. The stock Canon plug wouldn’t clear the tilt frame, and the cables constantly tangled on everything. So I took the last of my Ebay cables from building the T2i video downlink for my KAP rig and made a custom cable for this camera. Since there’s already a shutter cable running from the video transmitter to the camera, I made them both the same length and zip-tied them together. Now they’re one neat little bundle that fits fine and doesn’t cause tangling.

Custom Video Cable

Track down that @$%! NOISE!!!

I mentioned the servo noise in the section on replacing the voltage regulator. I got most of it, but not all. The pan axis continued to exhibit noisy behavior that I couldn’t track down. After double-checking the UBEC (fine), I tore the transmitter and receiver apart.

Here’s another one of those areas where hobby bleed-over is a good thing. A while back I bought a cable on Ebay that lets me use my RC transmitter as a controller for RC flight simulators on the computer. It came with a bunch of different plugs for different transmitters. When I got it I plugged in the one for my radio, and I was up and running.

The cables work by picking up the pulse coded signal off of the radio and turning it into positions for each of the axes via the USB port. Aha! What a great way to test the RC transmitter! It turns out I had a Hitec plug for this cable, so I plugged in the transmitter and took a look. The potentiometer driving the pan axis tested out fine on my meter, and when I tried it with this cable, it came out completely clean. Most radios tap the pulse coded signal right before it goes into the transmitter electronics, so at that point I figured the transmitter was fine.

The receiver also turned out to be fine. For what it’s worth, the noise filtering on the Hitec 75MHz receivers is remarkably clean – almost pretty. This one was no exception, and tested out fine. No blown caps, no cold solder joints, no scorch marks. Nothing!

Eventually I broke down and tested everything using an independent radio, battery, and servos out of my parts drawers. The only pattern I found was that the pan servo on the camera head started to have jitter if I plugged in the tilt servo from the camera head. No other combination caused the noise. And it didn’t matter which channel either was plugged into. The tilt servo was the culprit!

Unfortunately the only matching servo I had was in my KAP rig. For the sake of the project I gutted my KAP rig and installed the new servo in the camera head. It tested out fine. But I had to order another servo for my KAP rig!

After re-installing all the servos, tying down all the wires, and bolting on the upper deck for what I hoped was the last time, I gave it a test run. Jitter free at 250′! YAAAAAY! The noise was finally GONE!

Lock it down and send it home!

The last step was to remove every single screw in the thing, apply blue Loctite thread locking compound, and replace it. No sense having this thing fall apart in the field! I also neatened up the wire runs, tied down the servo wires, and applied rubber to the spots where the camera would contact the camera mount. At long last, the offroad camera was ready to go home.

6WD DSLR Revised

This was, and continues to be a fascinating project to work on. I’ve learned a lot in the process, and will doubtless keep learning as I service this in the years to come. But for now I’m ready to fix my KAP rig and get back in the air.

– Tom

2 Responses to “Offroad Camera Project Revisited”

  1. What a cool rig, love the photos.

  2. Hi! This is my first visit to your blog! We are a group of
    volunteers and starting a new initiative in a community in the same niche.
    Your blog provided us valuable information to work on.
    You have done a outstanding job!

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