Is the idea to use this inside water-filled pipes? The tether is made to be approximately neutrally buoyant, and should also have significantly less friction in a smooth, wet pipe than it does on rough concrete.
A bit concerned that if you lubricate it you could leave some residue in the pipe you’re inspecting, which might not be ideal - might be better to focus on stronger motors or a gearbox if you don’t have enough torque to pull it. Lubrication also makes it much more frustrating to store and unravel things - generally you lubricate things that are moving in a constrained and consistent place, not something that you’re going to roll back up after each inspection and get yourself covered in lube.
If you find you still need less friction, you might be able to get some kind of teflon coating/sheath for your tether. That’s probably quite expensive to do, and I’m not sure where you’d get it done, but might be worth considering.
The tether rough surface results in high friction. I use a standard Cat cable for pipe inspection as they have a smooth slippery surface when wet. The cat cable is negative buoyant and will be laying on the bottom of the pipe.
Greasing the cable is not a good idea…sand and dust will stick to the cable. Also, forget about the midline wheels. They will be stuck if there are any mud/debris in the pipe. As a base case you should avoid all and any add-ons to the tether. They will only create problems for you.
You could also use a 3mm SM fiber cable…
Did you build the tractor yourself?
What is the weight of the complete crawler setup?
I have built something similar but went with a tracked solution and it weighs in at around 5Kg.
I use it for confined space inspections and needed something that had a bit of weight to tow the tether around pillars and underfloor stumps, and having something that had a bit of weight helps.
I have yet to waterproof it as the electronics are not in a sealed compartment.
My tether is just plain Cat6 cable and I have yet to go further than 50 mtrs but it is fine with that.
I have a similar rover for pipe inspection. No pulling problem for 200m if the cable weight is less than the rover. A cheap AWG24 twisted pair or the Fathom X works fine for 200m.
