Let's Make Robots!

Tri-wheel stair climber

It seems to me that for a robot to be really useful in the home or workplace then it must be able to handle stairs. With this in mind I want to design a stair climbing robot chassis. This robot is my first experiment with Tri-wheels.

The chassis is just 4x Wild Thumper 75:1 motors driven by a Wild Thumper controller in a clear acrylic base. As this is only an experimental platform for the wheels I am controlling it with a TV remote and an IR receiver.

This first set of Tri-wheels is made using a new 80mm diameter wheel that has been produced by DAGU. The gears are steel to handle the high torque required when climbing.

The clear triangular frame is made from 3mm thick milled polycarbonate. I used CNC milled polycarbonate instead of laser cut acrylic because it is tougher. The acrylic is fine for the chassis but too brittle for the wheels. All shafts are ball raced to reduce friction.

You can see here that the chassis consist of 4 ribs, a top plate and a bottom plate. They are all held together by 56 small steel angle brackets and 112 small M2x5 screws that give the chassis good strength and rigidity. In hind sight I could have used less but this is just a prototype.

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Looking closer at the gears reveals that it's actually done right.

Perhaps gear up the wheels, would give the tri-arm rotation more torque, making it more likely to flip over forward.

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.

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!

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.

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.

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.

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.

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.

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


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.