Hi All. I am new to Vex, and not doing competition; just building bots for fun. I’m a software guy, not a hardware guy, and definitely not a physics person.
I dinked around with the sensor bot or whatever the thing in the basic guide is, but didn’t do much besides add more bumpers and sonar and do some test coding around that. I wanted to build a bot that could go upstairs and bring messages to my wife (what woman could resist a message delivered by a plastic robot?). I searched the forum, found a link for an awesome looking European bot that has 5 spoked legged-wheels. That bot A) climbs stairs, B) cruises over rough terrain quickly, and C) generally looks pretty freaky.
My bot took 36 versions to climb up to the top of the stairs the first time, and looks like a drunken rugby team team loosely tied together at the waist, staggering down the street at 2 am. Other than that, it’s exactly like the European bot. Exactly. 
Video:
(for anyone not downloading the .mov file, this is basically a two-piece, flat chassis. The two chassises can roll about 30 degrees independently, to help get over obstructions. There are 4 motors, using a 12:60 gear ratio, each powering a “legged wheel” 34 IQ holes in diameter, with 4 spokes to each leg. Household string near the tips of the legs helps prevent legs from lodging directly up against a step. The whole thing is maybe 2 1/2 feet long and maybe 15 inches wide at the widest.
Good things:
- It can get up the stairs, most of the time.
- It actually is really good at getting over various shapes and sizes of obstacles, including bean bag chairs, junk my kids leave around on the floor, etc.
Some issues:
- I had to make the leg-wheels really long to get over the problem of the robot flipping over endlessly as it climbed the stairs. I also continuously expanded the length and width of the bot as the wheel/legs got longer. These changes ended up adding quite a bit of weight over time. The ‘legs’ are 2x bars, doubled in width. Even so, they are quite weak, at the current length.
- I wanted to do 5-spoked legs, but could only manage 6- or 4- spoked legs, given the patterns enforced by the gears I built the wheels up from. The 6-spoke wheels were much smoother in motion than the 4-spoke wheels, but I couldn’t get them strong enough to survive the stairs. Aside from 3D printing a piece that has the correct angles for a 5-point star, any ideas?
- I had to gear down to the 60T gear, just to keep forward progress when at a slope. That means it’s really slow when traveling over nice flat ground. Given that each of the 4 motors works independently, having 4 gearboxes, and then 4 motors to switch them, seems impractical. Other than switching the V5 motors (which is a definitely possibility), any ideas?
- Even with the 60T gear reduction, it just barely has enough torque to climb a set of stairs. I couldn’t find anything in IQ with more than 60 teeth. Was there ever maybe a bigger gear for IQ that I might find on eBay or something? It looks like there is an 84 tooth gear for V5.
- Overall, it is now pretty fragile. When the legs were half the current size, it could flip over (which wasn’t good per se) and keep right on trucking. Now, if it flips over, it’s part city! Unfortunately, it’s already so heavy I can’t add any more reinforcement and still get up the stairs.
Would v5 steel parts be lighter? Or just stronger? Any advice in general before I break this little fellow down and start on a new design?
