Let's Make Robots!

Totally Lost. Totally, totally lost.

What I need is a wheeled, remote controled machine that can go into crawlspaces as little as 4" high and as tight as 4" wide, grab a line securely, and allow me to drag the line out. Estimate that the maximum the wieght should ever be is about 5lbs, with forward and aft cameras and lights (assume the microscopic "spy" type cameras and only a few inches of veiwing area for the light).

 Can someone tell me how to build one that meets these specifications? Please consider that I've never even TRIED to build anything vaugely like this before in my life (the most I know is having skimmed over the direction to assemble such a machine, but didn't look too hard becasue someone else was building it), so go slow and use samll words, please.

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Hello Andering,

just a thought and assuming you want to pull the cable out the same place the robot went in.

I think, that if you make it tethered, it does not really need to pull, if you make the tether out of say fishing line it would be light and flexible, you would drive the robot in, three wires attached to the tether, you could superimpose commands on the power or just run 4 wires.

Drive the robot over the cable, “Clamp on” and then pull the robot out by the tether.

You can get 5lb of pull from a robot weighing 5lb, but the pull will be very dependant on the surface, with a tether the limit is the breaking strain of the line or the cable gripper.

This would simplify the robot, no batteries on board, little intelligence on board required (de-serialize commands); the issue now is the gripper design and making it rugged enough to pull by the tail.

All the best



Allthough im new to this sort of thing myself, i have an idea.

it is hard to write what my mental image of it is,but im going to give it a try anyways.

1. for a camera you can use something called Flight cam One, it comes in different packages, but i recomend the one with steering and a monitor, done by a 2,4ghz wireless system. for lights, use ir or white diodes

2. make four platforms with four wheels on them (probably someone with pretty rough, but soft tracks) and connect those wheels together and to a brushless motor which is then connected to a speed controller, you would probably need a gear ratio to make it be able to drag the wheight, and not go so fast.

3. make a frame for the thing, preferably in steel as you would need all the weight you can get. since the width of the thing should be less than 10cm wide and 10cm heigh, you should make the frame plus the four platforms at that size.

4. buy 8 heavy duty strong torque marine servos (20kg +), and mount two on the backside of each "wheelplatform" with a lever in between the servos and the platform. Mount the servos to the frame. You should probably make some gliders between the platforms, as to stabilize them.

5. mount the flight cam package on the frame somewhere, so that you get 360 a view area. or at least front and back.

This way you have the posibility to  adjust the pressure of the wheels to the side of whatever area you are in, you can also adjust the pressure to front /back of the vehicle if you want that. and the with and height of the vehicle is adjusted with the servos.

for the motors you can use 3 y-connectors and connect them together into one channel on an radio reciever, the same can you do with the servos of each platform. 


to get a hold of the wire, you could use another heavy duty servo on a heavy dutyclamp or something, i dont know really

You would also need some pretty advanced and expencive radio equipment with many channels for this, the way i thought of it. Or maybe a roboduino or something allthough im sure how those work myself. 

most of the things ive written here are things you can get from different hobby stores.

I've also envisioned it to be around 30cm long, so you would have room for the things. 


You might also look in to some cheap rc tanks, and scavenge the belt drives from them (as long as the belt is rubber and deasent), instead of using wheels..


I really dont know if this helps any, but thats my idea 




A starting point might be to try to build 2 sets of tracks simlar to this robot :


Except instead of the body in the center, flip one track and bring the 2 of them together. Might shorten the tracks a little to make turning easier. This would be a little over 4" wide. Place a camera on a vertical plate between the tracks and a gripper too. If needed the gripper could be rotatable. It would probably be best to have this tethered, so that it could be reeled back in in case of problems. 

Sounds pretty ambitious. Totally doable, but ambitious. Requiring much patience. :)

I would break the problem down into manageable chunks and work on each chunk independently (although considering how each subsystem interacts with others).  That's how systems engineers build complex things like space shuttles.  That's how to eat the proverbial elephant a bite at a time.

So, one area to think of is the chassis.  Next, locomotion and steering.  The remote control system.  The grabber device.  And finally the video camera system.

You might be able to use off the shelf components rather than building from scratch.  E.g., can you use a RC tank of some type?  Or RC rock crawler?  You can definitely use off the shelf RC radios/controllers/etc.  The grabber may be something you have to make.  I would think there are wireless low light video cameras that would work.

Another thought... you may be able to find a similar / equivalent solution that is simpler to build.  More manual in nature, but using some electronics to help.



Check out the Versatrax 100 from Inuktun.  Fits the 4" space and has a 24 lb payload. Somewhat expensive, probably 4 or 5 figures.

Alternatives might be getting some Lynxmotion tracks (though 2" wide) and build something with their sprockets, hubs and motors that could pull what you need. You might only need 4 wires (2 control, one camera, ground) for a tethered control. 

You haven't mentioned distance, only space width, height.

Lengths shouldn't reach over 100'.
Is it a homework assignment? :)

Does it need to weigh 5 pounds, or be able to pull 5 pounds?

Is the 4" by 4" specs a round tube? A square tube? Is it even a tube, or is it a cave with minimum dimensions at different points of 4"?

Does it have to be wireless, or can it be tethered? If wireless, what does the range need to be?

Private use or business use? Any climate specs? It's not for a spaceship is it? MIL spec?

It needs to be able to drag five pounds. I assume that means it will have to weight more than 5, but then again that's sort of why I'm asking for help.

If it's tethered, it would have to be a long tether; About 100'.

Private use.

Hot and hot in summer (100+º), cold and wet in winter (lowest I know of was -20º) with some snow, some rain.

For use in home cable laying (no exotic enviroments, non mil-spec).

If this is for business use and needed soon you could skip the learning curve and get someone to make it for you.

If this is for personal fun and fulfillment start small and work up. Of course nobody is going to stop you trying it anyway, the best any of us can do is give some advice.

As long as the robot doesn`t need to turn inside the tunnel you can simplify it down a lot. Some wheels, gear motors, 2 miniature wireless cameras (why 2?), some white LEDs for illumination. It doesn`t need to be automated, just get some cable and make it tethered to a control box. Is the cable hanging down vertical or lying flat on the ground? This will affect your gripper design. Once the robot grips the cable, pull it out slowly by it`s umbilical cord.