R/C Rock Crawler Prepped To Become Stair Climbing Robot


[Starlino] is working on an autonomous mobile robot. Like many before him, he looked to the radio controlled car world for a base frame. He found a good candidate in a rock crawler model called “Mad Torque”. Crawlers have been around for years, but they’ve recently been getting more popular. As always, popularity leads to lower priced entry-level models, which puts this crawler at a reasonable price for a robot frame. As the name implies, rock crawlers are all about crawling. Relatively low speeds, locked differentials, four-wheel drive, and (optional) four-wheel steering.

Of course, [Starlino] had to test drive his frame out before tearing it down to install electronics. As long time R/C modelers ourselves, we can’t blame him. Testing uncovered one major problem. The Mad Torque wasn’t quite mad enough to climb the stairs in his house. The front tires would grab and pull over the first step, but the wheelbase wasn’t quite long enough for the rear wheels to grab hold.

[Starlino’s] solution was to extend the wheelbase. For most 4WD R/C cars or trucks this would be a major problem, as the motors are mounted amidships. An extended wheelbase would mean also extending the drive shafts or belts. This isn’t a problem with rock crawlers. Crawlers need to support huge amounts of suspension articulation. Rather than create complex drive linkages, the common design is to place an electric motor on each axle. This isn’t the greatest idea in terms of unsprung mass, but it does make for easy wheelbase changes. [Starlino] found that the design was so modular he could bolt a second chassis up to the original. The new rear chassis bolted to the front at the top shock mounts. An extra set of battery brackets formed a lower brace. The new extended truck was long enough to clear the steps, though it does still struggle a bit, as can be seen in the video. We think larger diameter tires might help a bit here. [Starlino’s] next step is to ditch the R/C unit and give this ‘bot a brain!

21 thoughts on “R/C Rock Crawler Prepped To Become Stair Climbing Robot

  1. As i’m from the rc rock crawler world, i say that pimp cane chasis is the best for this objective of stair climbing. a 40 series tyres sprecificaly ( hot bodies rover soft) that are the more soft and rubber quality is good enought for people to thoght they glue to the ground. I don’t see unsprung mass problem as said in here, with moa (motor on axle) setup as long as it is mounted on a pimp cane, but if it is mounted on conventinal shocks yes, it can be a small problem. It’s pretty easy, get lots of ground clearence, no need for shocks ou conventional suspension, and you can choose about 2fwd , 2rwd or 4wd. 2fwd can be more important than you think.

    Anyway my post is not to be seen as bad critic, but as as an idea, in my opinion.

    1. Clod stall could be a problem too, you need to get on that. As for unsprung mass, it is more of a problem for high speed driving and a lot of crawlers add weight to the tires myself included. Dig is another thing you might want to add. Lion pointed out this and it can give you greater control climbing stairs, something I learned from climbing stairs with my crawler. And last is the rear wheel steer, hitting the stairs headon can be more challenging and having the ability to move one axle a inch to left or right can be a huge game changer. The RC hobby is a great place to get parts for robots but you can also pick our brains too, sometimes we come up against similar walls, why not use others experience to expedite your project.

  2. I really hope he didn’t pay $145 for each of those Mad Torque RC rock crawlers. That seems ridiculous. I’m sure for $290 you could gather all the parts needed to mad a stair climbing robot. Anyways neat project. So far so good, the real fun will come when it’s autonomous.

      1. Actually just to reinforce my point. This “hack” uses an Exceed Mad Torque crawler as its basis, Exceed themselves now offer this: http://www.nitrorcx.com/03c20-madtorque-6×6-red-rtr-24g.html
        The actual manufacturer now have this so called hack as a factory option, but they dont stop there, they leave the rear axle on both frames effectively making it a 6×6.

        I dont care how common the comment is, but this is literally not a hack when the manufacturer offer it as a factory option yet outhack the poster in the process.

  3. How about an ‘inchworm’ mod? replace the battery brackets used to for the lower brace with a leadscrew stepper setup, so the spacing could be changed – extend it and engage the front wheels to climb the step, stop the front wheels, retract the leadscrew while engaging the rear motors – to go down, a similar sequence.

    1. In this case, it’s just angle gears. The spider gears are replaced with a spool, usually.

      In the case of a full scale crawler, you usually want a way to unlock the differentials, because it makes maneuvering easier. So an air or electric locker would typically be used.

    2. in this case diffs are locked permanently. in 1/1 there is a problem because the when directional axes are turning, the distance that the inside wheel run is smaller than the outside wheel, and it can lead to axle/transmission damage. And it is way more complicated turning because the veichle front slides out of the turn, increasing the turning radius


    I’m not a rock crawler guy, but I am impressed that there are that many of you watching and ready to pounce with good advice. If I were going to d othis kind of build, I now know I could hit up some RC forums and learn a thing or two before proceeding. Much like RC planes for me.

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