Let's Make Robots!

Tri-wheel stair climber MkII

climbs small stairs and rough terrain

After the MkI chassis bellied out on the stairs I rebuilt the chassis to give an extra 55mm (about 2inches) clearance in the center. The new chassis is also 50mm wider and a little bit shorter to help improve turning on the spot.

Unfortunately the result was almost the same as the wheels seemed unable to get enough traction. I think a big part of the problem is the 28 steel gears in the tri-wheels which combined weigh about 1Kg (2.2lb).

We took the chassis outside and found it could handle smaller steps and rough terrain ok. Looks like I just need bigger wheels for bigger steps. Looks like Wild Thumper tires are the next thing to try. The diameter is about 64% bigger and the knobs on the tires should grip the carpeted steps nicely.


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Look wht I stumbled over that reminded me to this MkII.

A two-wheel stair rover. Not the same - bot not too different to MkII.


Video here.

Interesting, although it looks like it would belly out on steeper steps.

I like your design , I find it really cool . 

And I think I have and Idea to save you battery .

If the height of the wheels was variable someway so as the front wheels could touch the back wheels 

then when the vehicle drives on a flat surface you could only power the back motors and move the whole thing 

without using the front ones . In this way not only you could save power but also you could produce 

a bit power on the front wheels because of the front  wheels moving and charge your batteries ...

What do you think ,is it feasible ? :)

No, this is not possible. the gear ratio required to produce the torque when climbing means that the wheels are effectively locked when there is no power. Actually it would use a lot more power as your are trying to turn your front motors into highly inefficient generators.

Hey Russ, can you possibly in your next video also show it going down the step/curb?

I took the clip, and washed it through a video editor at a frame by frame rate to analyze the climb, and would really like to do the same going off the step. If its too much trouble no biggie, but there may be more to learn from it before you make any more changes.

Also-Has the chassis or motor suffered any damages or excessive wear?Looks like it might be tough on the gears, but perhaps not.

As for me-I like it! Up to your normal standard of cleverness.

I'll try to post a second video when I return to work.

I have used thick steel gears in the tri-wheels as they do take a lot of abuse and high torque when climbing.

Sounds like a serious case of lack of traction, are the wheels made out of a soft or hard compound?


Also, what's the refrence for those motors in the pololu website?

the tires are a soft compound but the size is only 80mm.

the motors are DAGU motors that are custom made for DAGU. I know Pololu have similar motors but I don't think they are as powerful.

I mean dagu website... damn, have to sleep more.


Are they the 300rpm or 130rpm ones? I have something in mind and these motors/gearbox combo might be ideal.

The 75:1 gearbox does give you about 130rpm on the output shaft. Our newest motors have a quadrature encoder PCB on the back of the motor and provide 1200 counts per revolution of the output shaft.