I've been kicking an idea about a treaded robot around since last Thanksgiving. I purchased four of these nice geared motors
during Pololu's Black Friday sale.
I'm hoping to follow in Amada's tread tracks
and use these motors in a treaded vehicle.
Besides the motors and a couple of motor controllers
, I also purchased two sets of Vex's Tank Treads Kits
In order to mount the Vex sprocket to the motors' axles, I used a method similar to the way I mounted Vex Mecanum wheels
to my Rover 5. I drilled out the center of the sprocket to the size of the axles and then drilled a hole through the side of the sprocket for a setscrew.
I added a nut so the setscrew would have something solid to push against.
With the screw and nut in place, I filled the side of the sprocket with Polymorph.
Below is a photo of one of the sprockets mounted on a motor with the tread attached.
Gordon has got me hooked on expanded PVC
(ePVC). It's really easy to work with and not nearly as brittle as acrylic. Before cutting out pieces in ePVC, I first used foam board to see how well my pattern fit together. In the photo below, the foam board structure is farthest from the camera with the ePVC version closer to the camera.
I made a few changes after making the foam board version. Most of the changes were to the motor mount area. It's easier to see these differences in this next photo.
I also added t-slots in the ePVC version. The t-slots lets me use machine screw and nuts to hold the structure together. You can see some of the t-slots in my motor mount area in this next photo.
I used Polymorph to hold some of the nuts in place. The Polymorph also helps the ePVC not to be deformed by the nut.
There are two thin strips of Gorilla Tape holding a t-not in place on the right side of the above photo. In an attempt to get the t-nut to seat well into the ePVC, I heated the t-nut so it would partially melt the ePVC. I ended up burning the ePVC a bit.
I used 3mm (0.12") ePVC on the tread frame. You can see how I used double sheets of the 3mm material on some parts of the motor mount. I plan to use 6mm material instead of two 3mm sheets in these areas where I need more strength on my next revision.
This project is currently on hold until I get my CNC router up and running. While the ePVC is pretty easy to cut, cutting all the parts needed for these frames quickly becomes very tedious.
I also posted these photos at LMR
. Dickel, a LMR member
is working on a robot which also uses Vex treads
. I had told Dickel, I'd post pictures of my tread frame so he could see how I was using the treads. After seeing Dickel's robot, I'm trying to think of ways of making my robot look nicer.
One thing I think I will need to change is a way of adjusting tread tension. I'll either want to be able to slide one of the sprockets or wheels or perhaps add some sort of spring tension device. I'm hoping a sliding adjustment will be enough so I don't need to make a complex spring mechanism.
I don't want any of the frame to protrude past the tread. I'm hoping to be able to rotate the entire tread assembly so any side of the quadrilateral could be in contact with the ground (even the small side (when on tiptoes)). I'm not sure about rotating the treads, I just thought I'd add that part of the plan in case anyone wants to tell me it's a bad idea.
Did I mention I plan to have four tread assemblies? I'm not sure how they will be spaced yet. I'm hoping the final robot will be able to climb stairs. My initial plan it have this an indoor robot. I'm not sure how the Vex treads would do outdoors. I think erco has mentioned what a pain it can be to try to clean treads that have been outside. I'm not sure about the indoor only plan though. I might not be able to resist the urge to try the robot outside.
I'm hoping for some feedback on my current plans. I'm open to suggestions and criticism. So please, tell me what I'm doing wrong before I do it again four more times.