Electric Nickel Board

Project Description

We intend to build an electric two-wheel scooter with a 3D printed chassis. The scooter will ride on 4.9” diameter skateboard wheels and the drive shaft will be run by a 12 V high torque motor. The scooter will have a contact braking system in which friction slows down the drive wheel. The motor and 12 V battery will be hooked to a variable speed controller so as to be able to accelerate the scooter to a desired speed. If we have time at the end of the semester, we would like to add an infrared proximity sensor as a means for collision avoidance. The sensor would allow us to compute the distance of objects in front of the scooter and if the rider is approaching an object or person, a speaker on the bottom of the scooter can sound a tone to warn the driver.

Overview

We intend to build an electric two-wheel scooter powered by brushless DC motor. The scooter will have a speed controller to allow the user to accelerate to a desired speed. The main handle bar shaft will be able to pivot so that the user can manually vary the angle of the front wheel to steer the scooter. The scooter will have a brake on the back wheel so as to allow the rider to reduce speed through contact friction between the wheel and brake. Power will be provided by a lithium polymer battery which allows the rider a considerable travel distance on a charge. We have designed the board in three 8 inch long sections. The front two board pieces will have a robust connector on the bottom that will screw into the board piece behind it with 1 inch long machine screws. If the board is determined to be weak at these joints, we can reinforce the board by using a metal rod or wood plank. The handle bar and shaft will be purchased from a scooter manufacturer and will be made of metal tubing. This metal tubing will connect to a 3D printed part that connects to the front wheel shaft. The demo project we will finish with is going to be a 3D printed model with the wheel mounted on the edge. This will be connected to the motor and ESC.

Objectives

A successful scooter will be durable and able to withstand the weight of an average adult and be able to accelerate the rider to a reasonable speed. The speed controller should allow the user to choose the speed at which to ride and the brake should allow the user to stop in a reasonable distance. The battery should be able to sustain the scooter for a reasonable amount of time and the scooter should be able to power on and off so that it preserves battery when not in use. However, our goal with the time that we have is to simulate how the wheel would have spun using the ESC and motor combo. This will be mounted on a 3D printed stand.

Challenges

The main challenge of this project is going to be creating the CAD files to 3D print all of the parts so that they fit together. The printing of the parts will be challenging as the tolerances are quite small and we may need to print parts more than once in order to create a functional part. Also, we need to schedule enough time to print all of the parts as well as to have enough time to reprint them if necessary. The handlebar mount and front wheel mount will be difficult to design and will have to be sturdy enough to withstand the weight of a rider. User safety is an important factor as well as ease of use. Therefore, we need a means of acceleration that will stop accelerating the scooter in case the rider falls off. We need to isolate the battery and circuitry to minimize user injury by electronic failures. In addition, the break should operate smoothly so the rider can stop abruptly if necessary to avoid obstacles. The limited budget of $150 is challenging as the motor itself costs $50. Therefore, we had to pick and choose only essential parts for the operation of the scooter. Once built, the operation cost of the scooter should be relatively low with only the occasional need to recharge the battery.

Budget

• Motor and Speed Controller Combo and Lipo Battery, at $85.86 at Hobby King (link) (link)
  • The motor and ESC will power the scooter.

• Skate Wheel - $4.99(Blue)x2, at $9.98 on Sparkfun (link)
  • Skate wheels will allow scooter to move.

• Skate Wheel Adapter - Shaft Connection, at $8.90 on Pololu (link)
  • This adapter will allow us to attach the back wheel to the shaft of the scooter.

• Ball Bearing - Non-Flanged, at $6.61 on Karlsson Robotics (link)
  • The ball bearing will help and allow the front wheel to roll smoothly.

• Flanged Standoff B, at $8.98 on ServoCity (link)
  • Used to attach front skate wheel.

• Shaft - Solid, at $2.09 on Sparkfun (link)
  • Used to connect handle bars to the scooter base.

• BESTORQ Timing Belt, at $4.67 on Amazon (link)
  • Needed to drive the back pulley and shaft.

• Timing Pulley, at $8.95 on Sparkfun (link)
  • Allows the Back shaft to interface with the pulley

• Timing Pulley, at $11.59 on Amazon (link)
  • Allows motor to drive the belt

• Sparkfun shipping, $6.78
  • Shipping price

• Potentiometer, at $0.95 on Sparkfun (link)
  • Controlling speed

• Steel Sheet Metal Screw, Phillips Drive, #6-20 Thread Size, 1" Length, at $2.53 on Amazon (link)
  • For fastening

• Steel Sheet Metal Screw, Phillips Drive, #6-20 Thread Size, 1/4" Length (Pack of 100), at $2.83 on Amazon (link)
  • For fastening

• Irwin Tools Hex Shank Drill Bit, 7/64-Inch, at $3.49 on Amazon (link)
  • For drilling holes

• TOTAL = $164.21

• NOTE:

Due to the change on the week of October 31st, the new project only required the ESC/motor combo, the potentiometer, the Arduino UNO, and the wheel.

Team Members

Serra Erdamar, Andrew O'Sullivan (TA)

Gantt Chart

Design and Solutions

Communication

One of our main goals for this project was to successfully have an electronic speed controller (ESC) communicate with a motor. For this part we found the TrackStar ROAR approved 1/10th Stock Class Brushless ESC and Motor Combo (21.5T). This set came with five communication wires that we had to implement for proper signals. (can we include link to howto here?)

Another main goal for us was to implement safety measures. The first safety measure included a temperature sensor that is programmed to stop sending signals to the motor if it gets too hot. The heat corresponds to the amount of Watts exerted by the motor. Thus, when the temperature reaches above 46 degrees Celsius, the code uploaded to the Arduino will detect this and send the off signal. The second safety measure was an emergency "kill switch." We connected this switch to the battery and the ESC as the mediator in between.

Software (or coding)

An important part of the communication between all of the physical pieces is the code written and executed through the Arduino. To begin with, we had to include the Servo library to set up the ESC. We connected the temperature sensor to analog pin A2 to receive the values, 5V for volts, and ground to complete the circuit. Once we read the raw values in, I used a filter and conversion equation to print out the direct Celsius temperature values.

Assembly

To assemble the project together, we had to 3D print a few pieces. These included the holders measured out to the size of the motor and the wheel, respectively. These holders have holes implemented so we could bolt the motor and wheel onto the wooden board. Once this system has been assembled, we used another piece of wood as a clamp on the bottom of the board. To do this, we drilled four holes into each board and used nuts and bolts to hold it together.

Results

• Motor: Although we had a change from the original project, being able to send varying signals to the motor through an ESC and motorizing a wheel was one of the fundamental modules.

• Temperature Sensor: Using a temperature sensor as a safety measurement against excess weight on the board was another important component. I was successfully able to write and upload code to the Arduino that turned off the motor at a given temperature (29 degrees Celsius for the demo). Although the concept was executed at the demo, realistically, we would have wanted the temperature sensor detecting the rise in heat either by the motor or by the ESC. This was a decision made due to the fact that the motor and ESC didn't heat up significantly enough with the weights we were putting on to the board.