Cable tensioning mechanism that prevents autonomous electric-powered lawn mowers from running over their cable
Image credit: Adam H, Youtube
Darko SavicJul 04, 2022
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Cable tensioning mechanism allows autonomous electric lawn mowers to run without batteries and without running over their electric cable.
Why?
Batteries are expensive and run out of power too quickly for any serious lawn mowing work. Or else they are too heavy for home lawn mowers.
Batteries are the limiting factor for the strength of an electric mower.
Cable-powered electric lawn mowers are lightweight, efficient, and clean for the environment but can't be left unsupervised in an autonomous mode so as not to run over and cut their own cable.
How it works
An electric-powered reel of cable mounted on an autonomous lawn mower. The cable extends over an aluminium pole and through a pulley on top of it. The pulley freely rotates around its axis and points toward the direction in which the cable is pulling. It's mounted on a sensor that measures the cable's tension.
The cable reel is powered by an electric motor that keeps the tension within the desired range. If the cable is too loose, the reel tensions it. If it's too strong, the reel rotates in the opposite direction and releases some tension.
The lawn mower's software coordinates the cable tensioning with the mower's movements. When it's driving away from the power source the reel releases more cable at the same speed the mower is moving. When driving towards the power source it tensions it at the same pace.
At all times the cable is under sufficient tension so that the mower never touches it. It's long enough to cover the entire mowing area.
If the system detects any anomalies, it stops the mower and sends a message to the owner's phone.
When choosing between these two, I am not sure which one is more convenient. Cables can get tangled up in the canopy of trees, can get stuck or limit the lawnmower movement. Also, a 50-meter cable can get really heavy and seriously increase the electricity spent to power the lawnmower. On the other hand, batteries can be recharged many times and continue doing work without any serious interruption.
If we compare electric battery-powered cars and trolley-buses powered by electric chord above them, the latter definitely presents a thing of the past.
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Darko Savic2 years ago
The lawnmower doesn't pull the entire weight of the cable. It continuously releases more cable to free itself from pulling the cable behind it. When the cable gets too loose (no tension) it reels some of it back to create slight tension - thereby making sure the cable is lifted from the ground and will not get run over. The reel maintains ideal tension at all times.
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Povilas S2 years ago
While frequent recharging is rather ineffective, Darko's proposition can, however, be a temporary solution.
Another thing I thought about of similar regard that you mention here is that even though such a system would prevent the mower from cutting or entangling in its own cable, the long part of the cable behind the supporting mechanism would be dragged around the lawn frequently changing directions and shapes, this would be inconvenient for people and animals who walk in the vicinity, they could get entangled, stumble upon it, etc.
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Darko Savic2 years ago
Povilas S the cable only lays on the ground for the duration of mowing. Once the mowing is done all the cable gets reeled back on the mower and removed along with it.
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Alternative solution
Spook LouwJul 12, 2022
I was working on a similar idea recently, but ultimately I abandoned it because I thought something like this or this sufficiently solved the problem.
If the cable is attached to a rotor with a coil mechanism it will always maintain tensity, but the power of the lawnmower (or whatever else you attach it to) will be strong enough to uncurl the mechanism, while the spring mechanism will pick up any slack in the cable if the machine moves in an opposite direction.
I don't think you would even need to extend it much higher than the machine, by simply placing the mechanism on top of the machine the cable should never touch the ground.
The idea I was working on was to build a detachable mechanism that could be clipped onto any cable to do the same.
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Darko Savic2 years ago
I was thinking the same but when you get to 500+ meters of cable the reel would be pretty heavy which means the spring mechanism might not be strong enough (or too strong when there's not enough cable on it). So a motorized reel with plenty of torque might be needed
Darko Savic Jul 04, 2022
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