Watney Rover -- remix by callmelightningjunior

Last crawled date: 3 years ago

I'm listing this as a remix and a work in progress.
At this point it's the basic rover, I haven't mounted a camera yet. The quick assembly was to evaluate performance issues. Comments have been made about performance on carpet. The rover runs fine straight on carpet, but has trouble turning which seems to be a motor torque issue. I want to measure current to see if it's a current limit issue or something else. I also want to experiment with other turn algorithms other than the current full speed skid, and jog modes. I was concerned that the speed might be to fast, but in first impressions it seems ok.
I've got several remix ideas:
I want to put finer tooth gears. This should reduce noise and improve durability. Currently all the gears are 7T, which means the same teeth always contact, which can lead to uneven wear.
I want to add a better battery attachment than simply strapping one to the deck.
As far as software I'm interested on trying to create a program mode, similar to the old Big Trak, where the rover will behave like a remote rover where a set of instructions are given, then executed rather than direct control. If that is done this could have application as an education project -- simulation of an interplanetary rover, physical 'turtle' graphics.
Added new Gear Train
I've added an alternative gear train using finer pitch gears. The coarse gears are noisy and really "cog" (show a preferred position of tooth to valley).
The design went this way, I decided on making them 2 1/2 times finer -- guessing an initial module of 2.5mm (it turned out to be a little larger). This gives 17.5 teeth which allows a 17/18 pair. 17 is a prime number and 18 is not 17, so every tooth will mate with every tooth in operation. This should give more even wear. The final module turned out to be 1.14mm -- 3D printing is wonderful, who cares about standard sizes, just print what fits.
I printed the gear set on a raft to eliminate flash on the bottom edge
Assembly Notes
The wheel bearing surfaces were tight, so I sanded the holes with 600 sandpaper wrapped around a sightly smaller piece of rod.
I drilled out holes where possible with a #41 (~2.4mm) drill, and tapped 3x0.5, rather than trusting the screws to self tap. The Pi and H-bridge were secured with #4 x 1/4" sheet metal screws rather than the suggested 3x0.5 screws. Be careful not to over-tighten. I drilled through and tapped the motor block screw holes, and used 3x8 screes to hold it down. I had already stripped one of the short screws removing and replacing it while working on the gear train.
I put a small amount of grease on all bearing surfaces and gear teeth. I used Woodland Scenics HL657, but any plastic compatible grease should do.
I also printed two of the wheels mirrored so that there are left and right wheels,