First Bot: Drunken Stair Climber... advice?

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. :wink:

Video:
https://share.icloud.com/photos/0Yo6zY9iVIX1xxiTxilB9BOSg

(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?

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image
(no, no it would not be lighter)

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Steel is steel, no mater if it’s V5 or V4

The edr line does have 5 inch stair climbing wheels, not sure if they’d be usea level on IQ. You could also try compounding a gear ratio for more torque.
Instead of having each motor power one side, try having 2 motors per wheel and maybe leave the back set of wheels unpowered? Not sure how this would work, but it might?

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Not lighter but steel or aluminum parts would be much more robust and durable. Furthermore, less bracing / smaller bits can be built as construction will be stronger or “more permanent” persay.

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The Vex EDR “wheel legs” should be compatible with Vex IQ. While they only have 4 legs (as opposed to the 5 you are looking for) I think they could suit this purpose much better than your custom made wheel legs.

All this being said the only place you can get them is from RobotMesh or potentially ebay if you can find a deal on there

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@Gemeoa: I did find some references to those wheels at one point, but they were always listed as unavailable/discontinued. I’m 2000% sure that having wheels better than my crapalicious homemade ones would have been better.

@LilTree: Thanks for that info. I’ve never seen the Vex metal kits, but I assumed they would be stronger and require less double-bracing. I understand the power is 5x the IQ motors, so the combination of that might make this design work.

@Railgunawesome: compounding gear ratios! Of course. duh. I reworked it to do that, and I think it produced enough power to get up the stairs reliably. I say “think”, because the extra width/length I added to allow for the extra gears seems to have bene the last straw, and it disassembled itself rather enthusiastically each of the last 5 versions.

Having reached version 39, I am ready to throw in the towel (until I have EDR parts) and go on to a rocker bogie type rover.

Thanks all for help!

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I think that if you make the connection between the front wheels and the back wheels shorter, it might help.

I mean it might not fall over much.

The problem was that the legged wheels were so large, they have to be far apart, or they collide.

Here are a couple links for anyone interested. Really interesting mechanics:

Coyote III (I think I originally saw a video of the Coyote I):
https://www.wevolver.com/wevolver.staff/coyote.iii.rover/

European Space Agency rover with 2 legged wheels and a paddle-wheel thing in back:
https://www.wevolver.com/wevolver.staff/cesar/master/blob/Overview.md

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in your video, there are two ‘pods’ that consist of two wheels that are shaped like x’s,and there are a few beams holding them together. you only have one beam on each side, mounted like so: | instead,you should have two beams, together at a 90 degree angle like: |_