Project Overview

A number of years ago, I bought a remote-controlled (R/C) four-wheeled robot base but didn't end up doing anything exciting with it beyond assembling it and driving it around in the dirt a little bit.  Eventually, my brother and I began discussing turning it into a mobile rocket launcher - we grew up obsessed with Estes Model Rockets and still had many of them and all the necessary equipment.  Once I had some time to spare, I spent some quality time with some Futaba radio equipment, SolidWorks, a LaserCAMM, and some tools, and voila - I had a remote-controlled, four-wheeled, adjustable angle model rocket launcher.

Step 1: Establish Your Base

Before you start the fun part of designing the linkage and the launch platform, you first need a solid base.  I used a 4 wheel robot base kit that I had sitting around, but there are a number of possibilities here that could spice up the project - 3 wheels, tank treads, suspension, hover plasma thrusters, anything!

Unfortunately, I don't have any information on the base I used, so the photo will have to suffice.  Inside the black metal shell, you'll find 4 12V-200rpm motors controlled by 2 motor controllers with servo leads.  On the top of the body there are 4 threaded screw holes which we'll use to attach our platform base.

Also in this photo you can see the following, most of which we'll discuss later:
- On/off switch, charging port, and status LED on side of body
- Drive battery packs (white)
- R/C receiver
- R/C battery pack (red)
- R/C switch (hanging off rear of body)

In any case, because I already had the mobile base built (and because it wasn't my design), I won't talk any more about it.  You can decide what kind of base you want, and then move on to plan out what the electronics and the launch platform will look like!

Step 2: Electronics

I wouldn't say this was the most elegant electronics solution for this project, but it worked and you know what they say: "good enough is good enough."  Below you'll find a rough schematic of everything that has some sort of signal or power going to it.  I'll break it down by system for explanation.

R/C System

The R/C system (middle 1/3 of schematic) consists of the basics of any R/C project:
- a receiver (I used a Futaba 7-channel R138DP). The receiver is the "brains" of the entire system, giving control signals to everything else.
- a switch
- a battery pack that will ultimately power the launch platform servo. 

Drive System

The drive system (top 1/3 of schematic) is responsible for making the whole thing move around the world.  The components are:
- a battery pack
- a switch
- two motor controllers with their input coming from the receiver and their output going to the motors
- four motors, two controlled by each motor controller

Launch Platform System

This "system" only consists of a single servo - the one that will control the position of the launch platform and therefore the rocket.  The rest of this system is mechanical, and that's the focus of the next step.  Two important notes here: first, make sure this servo is strong enough, or is rated at a high enough torque to handle the launchpad - my first attempt failed to lift the rocket out of cruise mode.  And second, I used the throttle control stick on my radio to control this servo, which meant that due to its lack of springiness returning it back to the zero position, I could have the rocket stay at any angle between 0 and 90 degrees - very cool.

Ignition System

The ignition system (bottom 1/3 of schematic) includes:
- a battery pack appropriate for the required current for the ignitors
- an R/C switch - a circuit that only passes current when it receives a "HI" signal from the receiver - e.g. when I flip the switch on my radio.  I bought an RCE200 switch from Robot Marketplace, and it works wonderfully.
- the ignitor - I used an Estes Model Rocket Ignitor, attached to the wires by small alligator clips

Again, this was sort of a brute force electronics solution, but I wanted to focus my attention on designing a sweet launch platform instead of designing too much custom circuitry or hacking the mobile base kit too much.  The most notable way to streamline it would have been to consolidate battery packs and use voltage regulators and other components to achieve the correct levels.  If you design a better or custom system, please share!

Alright, let's move on to the mechanical stuff!

Step 3: The Launch Mechanism

This is the part on which I focused most of my attention, both because I see it as the crux of the project and because I love mechanical design!

Design Theory

There are many ways to make the launch platform's angle variable - horizontal in cruise mode, vertical in launch mode, or anywhere in between (for a more exciting launch mode?).  At first, I was thinking of attaching the servo directly to the blast shield itself, making it a simple hinge.  However, after considering placement as well as required torque to actuate the hinge, I thought a four-bar linkage would be a better choice.

The linkage I decided on is geometrically simple - the driving link and the coupler are the same length, and the idle ground link is the appropriate length such that it makes a 45 degree angle with the base when the rocket is at 0 or 90 degrees.  This turns out to be the length of the other links multiplied by the square root of 2, just like a 45-45-90 triangle.  With these parameters, the rocket's position on the mobile base doesn't change much at all when moving from cruise to launch mode.  Additionally, the driving bar in the linkage is vertical in launch mode, minimizing (or in theory eliminating) the torque on the servo from the weight of the rocket.  Check out the photos for a clear visual of the explanation.

Making the Parts

I designed the parts using SolidWorks and cut the acrylic with a LaserCAMM laser cutter.  The parts in the images below are numbered and identified below:

1. The base of the linkage that will attach to the top of the body.  The four round holes at the corners are for screws, the large hole at the center near the rear is for wires to feed up from the body, the three pairs of square holes spaced closely are for the linkage attachment pieces, and the pair of square holes spaced farther apart is for the servo holder.
2. Linkage attachment pieces - insert feet into holes on base and attach linkage bars through hole.  Note: there are 4 shown in the image, but you'll only need 3, since the servo is the 4th base bar.
3. Servo attachment bar - this is the only driving bar, since the other "driving" bar isn't driven by anything, and is just added for support.  Note the widening in the center of the bar - this is so that it sits on the base in cruise mode, allowing the base to hold the weight of the rocket instead of the servo.
4. Support "driving" bar - on opposite side from the servo attachment bar.
5. Idle grounded bars - note the length difference.
6. Coupler bars - these attach to the driving bar at one end and the idle grounded bars at the other end.  The launch platform fits into the notches.
7. Servo holder - servo fits snugly underneath.
8. Launch platform - serves as structure beneath the rocket and will hold the launch rod.  The 4 holes at the corners are to attach the aluminum blast shield, the larger hole at the center near the top was for wires to come through (though I ended up not feeding them through), the hole at the very center is for the launch rod, and the 4 holes surrounding that are for the launch rod holders.
9. Launch rod holders - these extended behind the launch platform with washers as spacers to hold the launch rod in place.

Once all the parts are cut and ready to assemble, you fit them all together like a puzzle (the beauty of putting in the design effort at the beginning!), and you've got a platform that smoothly transitions between horizontal and vertical.

The Finishing Touches

Now that we have a great launch mechanism, we can add the blast shield and a set screw to lock the launch rod in place.  I grabbed a piece of thin aluminum from Ace and cut it so that it perfectly covered the acrylic launch platform.  This piece is not only critical to preserve the acrylic, but it also makes the project look a little more heavy-duty.  Next, I super-glued a set screw on the underside of the launch platform in between two of the launch rod holders to lock the rod in place.  The blast shield is easily visible in the photos; check out the rear-angle side view of the project to see the set screw (silver with gold nut).

A final note for radio customization: I have a Futaba 9CAP radio that's highly customizable using the built-in software, and I did some tweaking to the settings to get the responses I wanted.  For example, I had to change the bounds of the throttle so that the stick all the way down meant the platform was in its horizontal position and vice versa for the vertical position.

Step 4: The Final Product

Here are a few images and a video of the final product.  Check it out, let me know what you think, and share your results if you make one too!

So does "no information on the rc base" mean you dont know what its called or where u got it? Ive been searching the internet for a week for an rc base. Ive wanted to do this for a long time just never got around to doing it. Good job!
man i like this alot,.. always wanted to do something like this and also do bottle rockets for 4th of July and New Years !!
nice! can the launcher be raised and lowered so you can fire it at say 45 degrees? <br>it would be really awesome if you could find some smaller ( very small) rockets and then set it to a low angle like an MLRS rocket launcher, you would need some method that allowed it to fire one of the rockets at a time.
I built a rocket launching pod to hang from the belly of an RC helicopter, but the guy who owned the heli never got good enough with it to fly long enough to shoot it at something... I ended up adapting it as a rotating mount rocket launcher for a PT-109 model, that I converted to radio control... That actually worked really well and I haven't seen any geese hanging around the pond ever since... The geese make a huge mess so regular PT boat patrols should make them think twice before pooping all over the yard... The rockets I made were about as tiny as Estes Rockets parts go... They were only about 5 inches long and I used the smallest micro engines they sell... I only intended to shoot it about 75-100 ft and I wanted it to fall to the ground as quickly as possible to minimize any collateral damage... We only fired it twice but both targets were completely neutralized...
That's the cutest death machine I've ever seen!
Very cool! <br> <br>I'm pretty sure you haven't broken any laws, but in the interest of safety ... if you make it possible to launch with the launch rod at an angle, please make sure it is no more than 30&deg; from vertical per the National Association of Rocketry Model Rocket Safety Code which can be found here: http://www.nar.org/NARmrsc.html
Thanks for sharing - I hadn't seen that before. Good stuff to know!
@tcone; Hi! You had me at R/C, Model, and Rocket. Most definitely tweeted! Cheers! : ) Site
Very nice, though it would look a hell of a lot better with tank tracks like the crawler for the for space shuttles that NASA uses.
True, tank treads are sweet. Maybe on the next iteration!
The base is an MMP-5 platform from The Machine Lab (http://www.themachinelab.com/). I know this because I used to work for them and build these before they moved to Colorado. Good stuff.
Yes! Thanks for letting me know. Heavy duty stuff they make.
they have these things for reall nasa type rockets. They only move at around 3mph <br>and are HUGE!!!
that thing is ready for battle! so cool, is it possible to shoot the rocket at an angle?
I haven't tried it, but I don't see any reason it wouldn't be able to! In fact, I lost the rocket to the high branches of the trees in the background on the inaugural launch; otherwise I would've tried it. It'll be my next move.
great! take a video!
This thing is probably really illegal. lol.
Yeah, that crossed my mind...I suppose only time will tell now!
cool i did it. and i could do it at an angle! Thannks!
You built one too? Share some photos or video!
spinroc1324, this is not your project - you are confusing me...
Very cool. I like what you have done here.

About This Instructable




Bio: Always looking for things to improve, repair, improvise, or modify. Studied mechanical engineering and physics at Stanford with a focus on robotics and international development ... More »
More by tcone:The Drink-O-Meter Reflecting on my AiResidency The QuickSilver (Ammo Can Silverware Organizer) 
Add instructable to: