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Tri-wheel stair climber

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OddBot's picture

As I explained to Gabriel, it was due to there being no load on the back wheels. Rather than lock when they hit the stair, they simply climb up the stair causing the whole tri-wheel to flip backward.

As the Tri-wheel is a differential drive system, if the small wheels can spin then they will. Once the load becomes great enough, the entire mechanism rotates instead.

Ro-Bot-X's picture

Very nice! Finally, an old Lego design that makes it to the non-Lego robots! I had troube steering with my Lego Tri-Star Wheeler (built after Doug's example, but with the large motorcycle wheels) because the Lego wheels have an inclredible grip and everything was shaking when turning. I ended up with 2 tri-star wheels in the front and a tail wheel and it was able to climb small Lego made stairs (just like in the above link). I was supposed to build a real stair climbing robot so the robot had to climb human height stairs then come back down. After seeing how it performs, I scraped this idea and used 2 rack-and-pinion jacks to lift the robot up the stairs and back down (with no turning at the top). But that was good enough for the competition. In real life the stairs have the bull nose that makes trouble for the robots climbing them. Anyway, I look forward to see the balancing tri-star robot! Cool, OddBot!

OddBot's picture

As you say, real life provides more chalenges such as bull nose steps (overhang) and cornering on small landings. I have some ideas that I am keeping secret for now. We will see how this first prototype goes.

mogul's picture

If you make the chassis longer, and able to fold at the middle, you would be able to climb much higher stair without make the tri-wheel larger by it self.

But it would require some work on the software side to make it auto adaptable to different stair heights.

OddBot's picture

The longer the wheel base the worst the robot handles corners such as stairwell landings. Ultimately I want to use only two Tri-wheels and a balancing system so that the base is smaller and can corner better.

The current base is only testing the wheel dimensions, torque, etc.

Maxhirez's picture
Cool idea. I agree-stair climbing is important for a homebot. This solution is probably more dependable than the spider security models. I can't wait to see the results.
OddBot's picture

The Tri-wheels are not a new idea. For now I am just testing the grip of the tires and various dimensions. This wheel will only be able to climb stairs of about 150mm (6 inches) in height. This limitation is due mainly to the size of the gears I am using.

If all goes well then in later models I will use larger gears (and maybe wheels) that can handle stairs up to 200mm (8 inches) high.

ossipee's picture

Most newer stairs here in the US are 7-11 seven inches rise 11 inches tread, so this might be tough if you want to sell it here you will have to have gen 2, [on the other hand Oddbot I so want to make a Mars Rover kind of thing or out door bot out of these], older stairs tend to have higher rises and shorter treads might affect the bot lenght, CTC will know more than me about stairs, I do heat and A/C but built my own home a few years ago so thus the stair thing, my basement has 10' ceelings


OddBot's picture

This prototype is using gears I had available so I think 150mm (6inch) will be it's limit. From my research, the U.K. had the heighest legal riser height of 220mm (about 8.5inch).

If all goes well and I develop this into a product then I will have to use bigger, lighter gears or a belt drive. The steel gears are too heavy. I will also need to experiment with different tires to see what gives the best grip on smooth stairs.

birdmun's picture

Damnation Alley, you may want to consider adding a pivot to the middle of the chassis to give it the ability to turn, or, keep the mass low so it can skid steer.