I will show you how to make your own RC car solely powered by a 16-foot rubber band. The model that I will be working on is based on the Black Mantis.
I have to say that the Black Mantis was an extremely fun project to work for 12 weeks. It consisted of three different prototypes and testing a lot of trials in the process. In the end, this was a satisfying experience which is the reason why I want to share this with other engineer students and hobby enthusiasts. Any RC enthusiast will enjoy building the Black Mantis. With its unique components, it makes easy to stand out from the rest. Also this a project that allows you to use parts from other projects. I must say that it is a quite complex project and time-consuming but it is a very rewarding project.
Key note, this is my first instructable ever so please don't be harsh. If you find any mistakes, please comment on them in the nicest way possible. Thank you, let's begin.
These are some of the Key features that make this RC car unique:
- Spoiler Brake Mechanism
- Adjustable Caster Angle
- Adjustable Body Length
- Air-less torsion system
- Power by a 16-foot rubber band
- Direct Drive
- It consist of a clutch as well as a breaking system
- It only uses two micro servos: 1 for the steering mechanism and the other for clutch/ Break system
Step 1: Gather Your Materials
1. Building Tools
- Screw driverHeavy duty plier
- Combination plier
- Husky Drill
- Drill set
- Exacto knife
- Sharpie Marker
- Super Glue
- Wood Glue
- Isopropyl alcohol (Must be 99%)
- Rubberband LupeMachine oil
- 4-40 Craftsman Tap
2. Electrical Components
- (1x) Rechargeable Lipo battery (Hobby people 7.4v 350mah lip battery)
- DHK Radio controller (Hobby People 2.4GHz Surface Radios)
- Receiver for DHK vehicles (It comes with the controller)
- (2x) Micro Metal gear Servos (MG90S Metal Gear Rc Mini servo) -must get this specific servo to fit into the parts.
3. Optional Materials
- 1/8" Thick Acrylic Sheet
- 1/8" Thick Acetal Delrin Sheet
4. Required Material
- 16 foot rubber band This is where you can get your rubber bands
- Metal fish wire
- 1/4" Diameter Solid Wooden dowels (As much as you can get!)
- 1/4" Diameter 7075 Aluminum rod (#90465K71)
- 1/8" Thickness Acrylic Sheet or 1/8" Thickness Plywood
- Zinc Plated Steel Round Head Screw (Order # 90279A115
- Natural Gum Foam (order# 93625K62)
- 1/4" Diameter Set Screw Shaft Collar (Order #9946K11)
- Abs Plastic Parts ( Access to a 3d Printer)
- Access to a laser cutter
- Plastic Bevel Gear order #7297K17 pitch 24, #teeth36
- Small Bevel Gear order #7297K15 pitch24,#teeth24
- Boca Bearing Boca website
- Stainless Steel Ball Bearings (Order #57155K377)
- One Way Bearing (Order #2489K22)
4-40 x12" Threaded Rod ( Any Local Hobby Store)
Step 2: Start to Get Your Hands Dirty (Front/Rear Wheel Layouts)
We are going to start to assemble the four wheels for the car. Download all DWG files posted on this step to begin.
DWG: For the front and rear wheels.
These files are for the rear wheels. (You can look at the videos for more reference)
- Rear Wheel_inner ring x 1
- Rear Wheel_Main Layer x 2
- Rear Wheel_outer rim wall x 5
The following DWG are for the front wheels:
- Front Wheel small front ring x 1
- Front Wheel x 2
- Front Wheel_ outer ring x2
Once you have laser cut all the layers necessary for this step, you are going to use tacky glue to glue all the layers of wood together. Any kind of wood glue will work. Make sure you align the rings and the other layers as close as possible so that the rubber can be uniformed to have better performance.
From my personal experience, I like to use super glue when putting the rubber on the wheels. I think it works great and the best part is that it takes only 10 seconds to do.
Step 3: Front Wheels Set Up
In this step we are going to compile the front wheels to the steering mechanism. Its hard to observe with the given pictures, but the steering part that holds the knuckle is adjustable.I call this the camber frame, just because you can adjust the angle of the camber. This is a great feature of an rc car since it allows you to adjust the camber at different angles and test for the best results.
Before you begin to assemble all the parts make sure you tap all the holes from all the 3d printed parts from this step and to all the rest of the steps that require a 3d printed part. The tab size is the 4-40 machine screws.
- Make sure you have the knuckle facing the right way. I use a 4-40 machine screw to serve as a pivot arm between the knuckle and camber frame.
- When putting the machine screw to the wooden dowel and the camber frame, you want to drill a small hole with the drill so that when you put the screw, it catches on!!!!
Step 4: Print the Big Parts!!
Ok, this is the step where I introduce the big parts. These are the crucial and most important components that allow the Black Mantis to run.
- Make sure that when you print these parts, that you tap all the holes with a 4-40 size tap.
Step 6: Make Your Spoiler Brake
Now lets focus on one my favorite part of this car, THE SPOILER BRAKE
- First begin by laser cutting the listed DWG files found on this step. Glue the left and right side of the spoiler with tacky glue. Wait for about an hour to make sure the glue is dry enough so the parts won't come out.
- Once the spoiler is completely dry, you want to begin to put the pivot arms underneath the spoiler and secure them with the 4-40 machine screws. (There is a total of 6, 4-40 machine screws.
- Once the pivot arms have been attached, you can put the bottom arm parts and use another machine screw to secure these parts.
- Cut about 1" in length from the rubber foam that is used for the tires. Put a tiny amount of super glue and put it under the spoiler. This is how you make an effective mechanism with a tight budget. This might not be the most sophisticated technology for a spoiler brake, but i can assure you that it works just fine.
Step 7: Clutch Mechanics
This is in particular one of the coolest features the Black Mantis can provide. Well, the clutch works as a slow break. Meaning the car can stop but it takes a few minutes to do so. Also, you won't have any control of the car when you fully released it, because you are releasing all the torque that is generated from all the winding of the rubber band. That is why I integrated a spoiler brake to help control the car.
The back servo serves to manipulate the spoiler break and the clutch simultaneously. When the brake is not engaged, the servo might engage the clutch or vice versa.
Step 8: Assemble Your Torque System
You are half way there to finish making the Black Mantis.
Now, I have to say that this is the most challenging part of making the car, so I will try my best to help you get through this. Ok, let's do this.
- To begin with, you want to get your hands on a 1" length and .25" diameter aluminum rod. In addition, you want to drill a hole in the aluminum rod. This will allow you to secure the rear nib tot the main back piece together. You need a machine screw to go through the nib all the way to the small shaft. This is to prevent the nib from slipping out.
Step 9: Put It Together!!
Step 10: Battery Set Up!
This is a crucial step to make an elastic rubber band car because a common mistake people make is misplacing the cables from the battery pack to your receiver and misplacing it can blow up the circuits. I had to learn the hard way to get this step right. So here we go.
The DHK receiver has four slots that you can use. We are going to use only three for this particular case. One for the battery and two for the servos. ( The steering servo and the Clutch/ Brake servo).
Make sure that when you plug in the battery that you insert the black cable to the right side. The black cable is for the ground, the yellow is for signal ( typically you don't need it for the battery) and the red cables is for the voltage being transmitted from the battery to the receiver.
Once you feel confident, plug in the cables to the receiver and start within the battery first as I am showing in the photos, then the steering servo goes all the way at the bottom. (Usually receivers would have st which stands for steering). Finally, the clutch/ brake servo in the ('Th') slot which stands for throttle.