Zero Mines is a group of people worldwide working on Open Source solutions for clearing land mines so people can grow food, travel, and live safely. Here is my suggestion.
Over 100 million land mines have been deployed around the world. Most of the places where these land mine are located are impoverished. The area that needs to be cleared is vast. The ideal solution would use cheap, easily available materials, that can be put together by anyone so that local people can quickly clear their own land.
The standard military approach to clearing a mine field is to use a heavily armored vehicle with a motorized flail to trigger the landmines. Armor is one way of staying safe while detonating a mine but not the only way. Distance is another.
A strong rope is cheap and can pull a heavy object across a mine field from a distance to detonate any mines. But you typically must go forward into a mine field. So how can you pull something towards you without first putting it in front of you? There is a very simple way.
The device I described fits those requirements. It is just a big rake rotating on a pivot pulled by a rope or cable from a safe distance to trigger mines.
1. place the pivot
2. pull the rope or cable from a safe distance or behind sand bags
3. sweep the rake over area to be cleared
4. move pivot / rake to cover more area
Dragging an object a distance from the arm would reduce the damage to the arm but even if the arm is damaged it is cheap and easy to replace. This might not be enough for all uses of the land or all types of land but can quickly clear an area for human travel and light use. If you need to go deeper use a heavier object and tines to dig up the ground.
Markus Kayser has built a 3D printer that uses sun light to turn sand into 3D glass objects. Free energy making things from the free materials.
He calls the device a Solar Sinter. The process works by spreading thin layers of sand then focusing a beam of light with a magnifying lens on a point to melt the sand turning it into glass. The object is built up a layer at a time. The movement and focusing of the beam is powered with photovoltaic but the high energy melting is done with a magnifying lens. This allows the device to be very low cost and potentially long lasting
A rover equipped with a solar sinter could be placed in deserts on earth or another planet and let run making useful objects. Even though this device makes crude items similar 3D printing technology has been used to make high precision objects of many materials.
In addition to a 3D printer, which is an additive technique, he has made a solar cutter which is a subtractive technique.
Ideas to make high precision low cost head positioning systems for 3D printer / fabricators / CNC machines. Precision stepper motors are expensive. What if you could use cheap analog motor? They could be very fast and cheap.
Run a length of wire along each axis of the printer / fabricator / CNC and measure the resistance at the head position. Using a table of actual resistance measurements on the device could increase accuracy and even heat differences could be taken into account. This could be extremely accurate and low cost.
Optical is another approach, this is how mechanical mice and mane printers function. Using a digital camera with distance measurements on a scale printed from a long format printer could make the device very fast and accurate. Using optics the accuracy could increased fine precision even with cheap webcam sensors.
Mounting an RF transmitter on the head and antennas at the corners of the tracks could allow triangulation of the head to extremely high precision even over very large distances. This is the same technique used by GPS and cell phone towers. The precisions scales with size and frequency transmitted.
Using opposing electrical currents to create a balance for any location along the rail. With the correct calibration this can be very accurate plus provide very fast movement.