Tracked Inspection Vehicles (TIVs)
In the world of Inspection Crawlers /Camera Rovers /Inspection Robots, or however you reference them, there are effectively only two methods of motion - tires, and tracks. Some vehicles are offered with your choice of either when purchasing. (Maybe someone will try a halftrack one day. No .50cal, please.) For purposes of this article, though, we will look only at Tracked Inspection Vehicles, or TIVs.
Most of us became aware of track drives though old tank warfare movies, or by seeing construction equipment or farm equipment. There are linked steel plate tracks, bound or continuous flexible rubber tracks, and hybrid steel tracks with rubber pads for road usage.
Track drives are an adaptation of wheel drives, and share certain commonalities. They both have an engine, some form of transmission, drive shafts and wheels. On track systems, there are generally two cogged drive wheels that claw along the inner surface of the track assemblies on matching grooves, holes and ridges. But instead of running around within the track loops in an infinite circle, they force the tracks to lay down in the path of the vehicle to serve as a continuous road bed instead. When you look at a tank or tractor from the side, you will see drive wheels at the end where the engine is. The others, which idle along and help support the weight of the vehicle, are “road wheels”. Larger tractors include some sort of articulating suspension, and may mount road wheels singularly or in pairs on sprung trucks.
These drives were developed to answer off road movement problems. Heavy wheeled vehicles have less contact patch surface area per unit of weight. The pressure against the earth is higher. Think of tracks as a sheet of plywood laid over delicate roof tiles to distribute the weight of a worker, vs plodding along on shoes. Tracks give more “floatation” to the vehicle. Where tanks and farm tractors have to operate on soft muddy earth, their tracks keep them from sinking in less than an equal weight wheeled vehicle.
In addition, the hard ridged contact patches can be optimized for increased traction. It’s a balance of weight vs traction and power.
Steering a tracked vehicle is accomplished by varying the speed of the left and right drive wheels. Differential speed is all that is needed. With opposite rotation, the tractor can “spin on a dime”.
Tracked Crawlspace Inspection Vehicles
There are a lot of tracked camera rovers. I’m not aware of any with steel tracks, but rubber and plastic units are plentiful. The majority of tracks include ridges for traction. I believe I saw one with knobs, but I don’t remember where that was. (I doubt very many people do…) TIVs use 4, or 6 drive /road wheels.
Miniaturizing active suspension for use on cam rovers is difficult. So builders forgo that in favor of flexible tracks that deflect between the wheels. This allow for some conformity to certain obstacles and types of terrain. Over time, some evolved plates along the sides to prevent material from entering the track channel and jamming the tracks. On these, you will not see much of the wheels.
TIVs follow a common design philosophy.
Each has a hull. This is box-like structure that houses the drive and electronics within, and the track systems without along the sides. The hull has a uniform flat surface along the top and the underside.
They are driven by independent electric motors, transmitting power through shafts in firmly fixed bearings or bushings, to drive wheels working with non-articulating road wheels. Some are direct drive motor-to-wheel. Because the wheels do not articulate, the vertical movement of the lower section is limited to the track flex itself. Properly built, these should not “throw a track”, which is when a track comes off the wheels.
TIV Pros
Maneuverability
TIVs can spin on a dime, the increasingly advertised “zero turn”. (Interestingly, hulled vehicles sporting traditional off road tires and wheels use a similar drive and also employ Zero Turn.) In-place rotation allows for some very interesting possibilities. Rotating the camera itself can be forgone in favor of spinning the whole vehicle in order to aim it, much like a self propelled howitzer. This is a simpler method of control, and eliminates one thing the operator needs to manage.
Payload
Tractors can carry and move a LOT of weight. Which goes back to full sized tanks and heavy equipment heritage, where payload capacity is hugely critical. For a TIV, weight can be found in the battery, and easily managed.
Surface Area
The upper surface of the hull provides a lot of area to mount equipment such as cameras, transmitters, antennas, lights, handles and cable deflectors (and even a battery). While the ease of attachment is attractive, getting hung up is a huge risk. Deflectors are an absolute must.
Terrain
Some inspectors inquire as to whether tracked vehicles can be used in an attic. Where insulation will not be compressed, or damaged when a TIV is retrieved by dragging it back to the operator with a tether, this is doable. Running along hard surfaces laid down for whatever reason, along already compressed insulation, batts with paper side up, etc…. is an inspector’s call. He has to consider SOP, need, benefit and damage risks in retrieval ops.
TIV Cons
Panning
Hull rotation of the camera means that the operator can not pan left or right, while moving, to gain more awareness of structure he passes. TIVs with camera rotation are superior to their counterparts for this reason. It’s a trade off between simplicity and utility.
Weight
If long run time is desired, it can only be accomplished via watt hours. This is true for any rover configuration. It is important that weight distribution is managed during the design phase. Tracked vehicles benefit from equal front to rear distribution, and a low center of gravity, if any significant grades are to be challenged. This is different from articulated wheeled rovers, where something along a 60/40 front to rear weight is desirable. If a TIV’s weight is biased rear, it will have a harder time on inclines, and may flip over trying to cross pipes on grade. If an owner experiences this, he can use wheelie bars, or add weight to the front, though adding weight will stress all components of the drive train to some degree.
Hull Height
Due to inherent constraints in the design, the ground clearance beneath a hull is limited. Under the right conditions, rocks, clods, debris and structure can fill the gap beneath the hull and cause one track to rise from the ground. This results in an undesired spin and requires powering the rover while steering to get free.
Ground clearance comes into play when in a moonscape with large blockages, and when in mud. Moonscapes are hard enough to read in person, they are more difficult via camera guidance. When any of us get hung up, we have to remember what we were crossing, and imagine how we got stuck. A hull that moves through water has one hangup that a rock crawler does not - suction. If the bottom of the hull slides along mud, it can suck down to it. At that point, it can only be freed by hand (no thank you), or by hauling it out via a previously attached tether.
Hull designs also affect overhead clearance. You may have a specific tolerance in mind. Check that measurement when shopping around. If you are a limbo fan, a TIV may not work for you. Consider you area’s crawlspace styles and determine what you would consider acceptable.
Camera Bounce
If you’ve ridden a regular bike, and then a quality shock-equipped mountain bike over rough terrain and trails, you know the value of suspension. Your arms, neck and other bits will demand the better bike. On a cam rover, the camera has a rough life. There is a lot of bouncing. This movement affects the pan tilt unit, component life and image quality.
I’m in favor of full stop photography.
Drive. Stop. Image. Repeat.
If you take moving video for later review and frame capture, bouncing video recordings will become your new worst friend. To pull good stills from a lousy recording, you will need a camera with excellent electronic image stabilization. RESEARCH what is offered to you.
But beyond that, there is navigation. Your camera provides you with the live video feed you use to drive. If the image is shaking rapidly, not only is navigation difficult, but your eyes may complain, too. When you watch a TIV driving video recorded while running on bad surfaces, watch how the image performs. The video shows you what the machine can see, and how it moves and spins. But it ALSO shows you what your first person view navigation may look like. Obviously, the smoother the surface, the smoother the feed. You area’s crawlspace conditions will determine your experience.
TIVs with active suspension will perform better than those without. TIVs with a wide vertical channel in the bottom of the hull will have better ground clearance. While I expect these options to eventually make their way into tank designs, I’m not aware of such a machine at this time.
Takeaways…
Is there a right or wrong in using a tracked inspection vehicle over a wheeled one? While I certainly favor wheels with live axles, I must defer to an inspector’s preference. I build mine for reasons most don’t promote - much. I was inspired by stories of injury and death. I don’t like those. As I get older, I appreciate life more. It’s my belief that older HIs, with massive experience but physical injuries or age limitations, still have a lot to offer. Being forced out of the crawlspace by physical realities, or dangerous conditions, or critters, or limited access, means he can’t deliver his client as full a report as he would otherwise. An inspector with a camera rover can extend his reach and ability.
But which rover? I’ll tell you all day long what is best, but in the end, it’s the tool a man is comfortable using that will be employed. The rover a man likes and feels good about will go into that hole, instead of staying in the box. Ultimately, the avoidance of injury, or electrocution, or unexpected panic, will come down to his choice to use a tool he LIKES, to collect that imagery for his client.
So which to chose? Simple. The one you feel good about. The one that you’ll USE because of that. The one that checks the boxes on YOUR list. Making that decision is one based on research, money, and yes - feelings. In the end, I want to see rover builders offering choices, and inspectors retiring after a full career, delivering good work, with as few injuries as possible. Get the rover that fits YOU.