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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I think I'm getting the picture, so basically it uses the weight of the bot and traction to "lock" the gears.... as long as the small wheels can get enough traction to transfer the torque to make the whole mechanism spin, it doesn't need any of that Rube Goldberg nonsense :). Then it turns into a "simple" matter of weight quantity and placement, and wheel size. You are right again, that is so much easier :p This is the first time seeing this mechanism, so it intrigues me. Keep up the awesome work.

Bad Ass, Odd Bot! Bad Ass!


Thanks Frits, always glad to entertain the troops :D

?....... is it me or are the rear "wheelies" going backwards when they should be going forwards ... i understand the mini wheels are going the correct way but the whole mech seems to be going backwards being counterproductive to climb up and lift the belly away from the step.......(G.scratches head).

PS. my latest house bot gets its belly stuck on the botton door sill ...and thats only 2cm high ...... i take my hat off too you when you accomplish the flight of stairs....

As I explained to Gabriel, because there is no load on the back wheels, the small wheels are not locking up when they hit the stair. instead they climb it causeing the whole mechanism to spin backward. When under load, the small wheels would lock when they hit the corner and the entire mechanism would rotate forward.

Interesting results, how many inches of clearance do you have to the bottom of the chassis?  You think the clearance will fix the issue?   Most videos of this type of setup usually only climb fake steps that aren't as steep, it's nice to see someone attempting the real thing.  I too want to build a tri-wheel design, I was thinking about driving the tri-part seperately from the wheel driver.  I realize one benefit of the design is being able to use the same drive motors and the gearing allows it to turn it around, but having a seperate motor might give other benefits as well, at the cost of complicating the design.

I can't find if you posted it elsewhere, are the wheels around 3 inches? and the diameter to the outter wheel centers is 6 inches?

I look forward to seeing it climb those steps, good luck.

This is the problem, the clearance on flat ground is only half of the step height. I plan to replace these wheels with Wild Thumper wheels. That will only increase the height by about 20mm (¾ of an inch) but it will also close the gap between the front and back wheels.

The wheels I'm using now are 80mm diameter (3¼inches) the Wild Thumper wheels are 125mm diameter (5inch). The diameter of the outer wheel centers is 170mm (6¾inch).

I might just be mistaken or misunderstand, but wouldn't it climb stairs a lot better if the "rear" wheels went in the opposite direction when it's trying to climb?

No, the wheels are working correctly, the stairs are simply too high for this robot. The reason the rear wheels appear to be driving backward is because there is no weight on the back wheels at one point so that as the small wheels drive forward and then up they cause the triangular frame to spin backwards.

If there was enough weight on the back wheels then the small wheels would lock when they get into a corner. this would cause the entire triangular frame to rotate forward rather than backward.

yeah, OddBot could try to add another gear on each arm to make them flip forward instead of backwards when they loose grip.