Finally got my little rover driving itself around the workshop

I've had a similar base rolling around my garage for about a year now, and the wheel slip thing bit me too, except mine was on smooth painted concrete near the garage door. Every time it turned on that patch the map would shear sideways. What ended up helping more than anything was slowing the rotation speed way down in the config, like half of what I thought it could handle. Slower turns meant less slip and the map stopped warping. Took me embarrassingly long to try that before messing with anything fancier.

On the gravel question, I can answer that one from experiance becuase I tried mine on the driveway last summer. Small solid wheels on loose gravel is rough going. It got bogged down whenever the stones were bigger than a marble, and the bumps shook the lidar enough that scans came back noisy. It coped okay on the packed sections near the gate where the gravel had settled. If your chassis takes common sized wheels, something wider with a bit of air in it makes a real difference, but that usually means a new motor setup too since the gearing on hobby chassis isn't made for it. For the screw pickup arm, mine eventually got sorted with a cheap suction approach instead of a gripper. Tiny screws on a hard floor are way easier to pick with suction than fingers, and there's no alignment drama.

On the gravel question, I can save you some disappointment. I ran a similar setup around my back patio and path for a few months and the loose stuff was rough on it. The wheels dig in on anything finer than pea gravel, the chassis bounces enough that the sensor readings get noisy, and the little motors run hot because they are constantly fighting for traction. Mine did okay on the compacted part near the fence but gave up entirely on the fresh loose strip along the shed, just spinning in place until I carried it out. If you ever try it, lay down a paver path first and keep the robot on that. Worked fine there. Indoors I took a diffrent route than lidar altogether. I put reflective markers at fixed spots around the room and let the robot home off those for positioning. Cruder, but dust on the floor and uneven traction stopped mattering much because I was never dead reckoning over long distances. Downside is it only knows where it is near a marker, so no nice map to look at, just point to point hops.

For the screw pickup idea, mine did that job with a simple magnetic bar dragged behind the base instead of an arm. Not glamorous, but it cleared every dropped fastener in the shop and never needed a gripper tuned.

Not sold on the suction idea for the screws. I tried that on my own bench bot and gave up on it. A screw is small but dense, and there's nothing flat for the cup to seal against, so it either slides off or the vacuum just can't hold the weight. Shop dust made it worse, the cup picked up grit and lost grip entirely. A magnet on a simple lever arm did the job instead, since screws are steel and basially grab themselves. Only catch is keep it away from anything you care about like SD cards or speed controllers, and it'll also hoover up every paperclip in the room. Cheap to try before buying a pump though.

The magnet suggestion lines up with what I landed on too. Mine is just a strong disc magnet zip tied to the end of a cheap servo arm, and it drops the screw onto a little metal tray when it gets back to the dock. Only headache I've hit is screws that land in the gap along the baseboard, the magnet can't get flat against them, so I end up kicking those out by hand. Worth leaving a couple inches of clearance around wherever the arm sweeps.