There’s been some verbal discussions on a rotor tiller tool among community members but there’s a few major barriers that need to be overcome before a tool like this can be developed.
Power requirement - the current electrical power available to the UTM is not sufficient to power a tool that will till the soil. I think the maximum voltage is 5V or 12V at the UTM. To till the soil 3” (7.5 cm) deep you will likely need a power tool at 8.5A and 120V. This is possible but you would need to run a separate accessory power chord to the tool.
The forces on the Farmbot tracks and structure may be too great for the tiller application. If it’s not perfect soil and there’s clumps of clay or there’s a stone or other obstruction in the soil it may create bending moments on the y-axis tracks. This could cause the aluminum tracks to bend or to jump off the track. It would also be hard on the Farmbot gears belts and stepper motors.
If you have ever used a rotor tiller depending on the soil it can create very unpredictable movements and it could cause reliability problems for the Farmbot and it’s structure.
Check out this video review of the Earthwise 8.5A Electric Rotor tiller and look at the movements of the tool while in use. It jumps and lerches forwards and backwards.
You could develop a shock absorber system that would accommodate the tiller on the Farmbot. It’s not impossible but Tilling is likely something that would be done easier by a person once or twice a year.
Just as a statement of fact, you can go to the Home Depot and purchase the Earthwise 8.5A Electric Rotor tiller for about $150USD.