microMVP: A Portable, 3D-Printing Enabled Multi-Vehicle Platform for Robotics Research and Education (V3)

Introduction | Parts and assembly | Software stack | Download manuscript (V1) | V1 Page

In designing microMVP, emphasis was put on making the system readily reproducible by robotics researcher, educator, and hobbyists alike. We did extensive study to ensure that the parts we select are reasonably easy to obtain, easy to use, and reasonably affordable. This is of course an evolving process and will continue improving the availability and affordability of the components of microMVP with each iteration. Below is a list of all parts used in the microMVP vehicle version 3, including some suggested wires and connecters for connecting the components. Note that reference prices are pulled in July 2018 and may have since changed. The price assumes volume purchase for building 10+ vehicles. The second table lists the few parts for the tracking platform.

Vehicle parts

Part name with link Description Cost (USD)
Vehicle shell The link provides an STL model for printing the shell of the vehicle. Depending on the printer used, the material cost varies. For example, using standard PETG material at $25/KG, the shell which uses 32grams of material, costs 0.8$. 0.8+
Gearmotor (x 2) Pololu 120:1 mini plastic gearmotor with 90-degree, 3mm D-Shaft output. 4.95 x 2
Motor driver carrier DRV8835 dual motor driver carrier board. 3.89
Arduino board Sparkfun 3.3v Arduino Pro Mini 328 running the 8MHz bootloader; with 8 analog pins; support auto-reset and status LED. 9.45
NRF24L01 Module This module uses the 2.4GHz transceiver from Nordic Semiconductor, the nRF24L01+. 2.20
32x7mm wheels Pololu wheels that press-fit onto 3mm D output. 3.95
Caster ball Metal ball serving as a caster wheel for the vehicle. 2.95
Battery Turnigy nano-tech 260mAh 1S 35-70C Lipo Pack (QR Ladybird/Genius CP/Mini CP) 260mAh lithium ion batteries 2.29
PCB board This link provides the Eagle file of our self-designed PCB board. It can be produced by oshpark 1.74
Switch Mini Slide Switch: 3-Pin, SPDT, 0.3A (3-Pack) 1.34
(Suggested)Break Away Headers - Straight Angle (10 pack) Connectors using for assembling. 1.80
(Suggested)Break Away Headers - Right Angle (10 pack) Connectors using for assembling. 2.40
(Suggested)Cables (1) Excellway® 100Pcs Mini Micro JST 2.0 PH 2Pin Connector Plug With 120mm Wires Cables. 3.19
(Suggested)Cables (2) Molex 51005 / 51006 2.0mm 2P cables. 1.90
Total   47.8

Tracking and control platform

Part name with link Description Cost (USD)
USB video camera Logitech C920 1080P webcam. Other cameras are also fine as long as the camera support the adjustment of parameters such as focus and white balance through driver interface or openCV. The price of Logitech C920 fluctuates but can be found at 60-65 USD. 60+
Microphone stand Basic microphone stand for mounting the USB video camera. 17.99
Crazyradio PA 2.4GHz USB dongle USB dongle used for receiving and sending message between computer and radio chips. Only need one for the whole system. 30
USB extension cable Extension cable for connecting USB video camera to computer (optional). 5.79

Putting together the vehicle

Printing and readying the shell

The shell (.stl) of the vehicle are two pieces, including body and cap, that can be printed on any working 3D printer. We tested printing on a 50K USD stratasys printer as well as a 180 USD monoprice mini 3D printer. Once the two pieces of shells are printed, the cap can be easily installed and removed at the top of car body. Below are pictures of the separately printed shell pieces, including body and cap, and the half assembled shell, which shows the direction to put cap on the body. The caster ball should be glued on to the bottom of the assembly as well after wheels installed (using only the ball assembly and the thicker 1/8" spacer).


Soldering together the components

The micro-vehicle requires the soldering of a few wires and parts on the PCB board, including the pololu DRV8835 dual motor driver carrier, the motors, the Arduino board, the wireless nrf24l01 module and switch. In order to make the vehicle more robust, we use break away headers instead of wires to connect each part. The schematics we use for connecting the wires are given in the picture below. Because the Arduino board offers more output pins than we need, the schematics for doing the soldering is not unique. Below is the schematic used for soldering.

After soldering, we would have a connected part of chips as following:


Installation process:

As you can see below, the motors and the PCB board can be soldered separately at first. Then put the motors in the lower space of the car body. When they are put in the correct places as shown in picture, you can simply plug in the connecting header to connect chips and motors. In this way, it would be easier for people to dissemble the PCB board without get rid of the motors on the car shell.



We also add one more set of wires together with battery wires for the charging purpose. It has been tested successfully for correct charging. But it is totally optional for you to include this design or not.

*Caution: in the upper space of the vehicle where the PCB board is installed, which can be narrow, be careful to avoid direct touch between charging wires’ sockets and PCB board. It can result in short circuit and the parts on PCB board can be broken!

Camera platform

The webcam can be mounted on the microphone stand (or other similar fixture) with many methods. We recommend using normal tape or masking tape, which are sticky enough and relatively easy to remove without leaving glue marks. There isn't much to this part other than that the camera should be placed at an appropriate height (1-1.2m), facing down, and connected to a computer. In one of our setup (to the right), we attached two cameras and use one for tracking the vehicles and one for taking videos.

A full setup with the camera platform and ten micro-vehicles are pictured to the right. Ideally, the environment should have reasonably even lighting and the floor should be relatively uniform. Some glare is perfectly fine, however, as was the case with our setup.
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