Introduction: Monster Masher

About: I work at RobotZone ( the folks behind Actobotics and ) in Winfield, KS. I love working on projects with my kids and seeing what they create.

This is a breakdown of a project I recently made for a Happy Halloween video at work ( I set out to make a project to crush larger sized cans that conventional can crushers could not handle. What I ended up with (a can crushing rover which can drive over cans to crumple/shoot them out) is not practical but fun.

I recently visited an awesome surplus store called The Yard in Wichita KS (which I highly recommend if you are ever in the area); there I found some big rubber washers which just spoke to me. I got a bunch because they were cheap and I knew I wanted to use them in a project. When the topic of can crushing came up at work I knew that I wanted to use them for a can crushing rover. I really liked the idea of having one mechanism which would do 3 things (pick up, crush, shoot) all in one smooth action.

Step 1: The Electronics

Electronically, this project is simple. It is basically an RC car with an added function. I am using:

Step 2: The Frame

I primarily used Actobotics X-Rail for the frame. While there are other extrusions out there like 80/20, the X-Rail integrates easily into the entire Actobotics parts library which is very helpful in a project like this.

Step 3: The "Wheel Legs"

I knew that the overall deck height and the angle of attack (the height of the first roller in relation to the second roller) would make a huge difference. So instead of hard mounting the drive motors to the chassis I created "legs" that I could easily adjust the angle of. This approach gave me the ability to quickly modify the height and pitch of the chassis as desired.

Step 4: The Gear Train & Rollers

The rubber washers have a 3/4" ID but were able to stretch enough to press-fit very tightly onto a 1" OD tube. Originally I filled almost the entire length of the tube with the rubber washers but after testing, I preferred how it performed with just a few rollers in the middle. Earlier in the project (when it was not geared down as much) I needed the 1" ID collars to keep the rubber washers from "walking" down the tube since the shear speed of the brushless motor actually caused them to expand enough to do so.

There are 3 stages of gearing. The pinion gear is 24 tooth, which is meshing with a 128 tooth (a 5.3:1 ratio). That shaft connects to a 48 tooth gear which meshes with a 76 tooth gear (a 1.583:1 ratio). This is connected to the bottom roller which means the bottom roller clocks in at about 11,842 rpm max. The bottom roller drives the top roller with a 1.6842:1 ratio (76 tooth to 128 tooth) bringing the top roller to a top speed of 7,031. That is a great deal slower than the 100,000 max rpm of the motor - but still stupid fast.

Since the distance between the two rollers was more critical than the speed, it was nice that I could swap out different gear combinations easily because of the slide-and-lock style of an extrusion based structure like X-Rail. Although that level of control is a double edged sword. If I had gone with Actobotics channel I would not have had as many gear combinations possible because even if two gears are compatible in the sense that they are both the same pitch, if you are mounting them in something like channel, the distance from one gear to the next has to be correct to mesh up. So it will either work perfectly or will not reach each other at all. On the other hand X-Rail let's you use any two gears that are of the same pitch but you need to make sure that the spacing is perfect between them for a proper mesh. And when you are working at ludicrous speed like this project, it is all the more important that everything be correctly aligned.

Step 5: Running the Beast & Closing Thoughts

This beast is loud and intimidating. It does a great job of grabbing the cans and chucking them up in the air while doing damage along the way. It is overall very fun and also pretty scary to drive.

I often like to close my instructables with some thought of what I might do differently if I were to start over or thoughts on improvements I might make in the future. This project may benefit from some side panels funneling outward in front to help guide the cans into the rollers. Also, (as much as I like the rubber washers I used) I do feel like if I had some that were twice as big it might work even better in the sense that I could move them closer together to get a more flattened result. However, there likely is a size cutoff where it would be too large to be able to pull up the cans while driving over them.