Motorized Scooterboard

List of group members

  • Dakota Rich
  • Ritchie Nicholson
  • Dustin Childress
  • Harold Balthrop

Abstract

This project consists of designing a motorized scooter board where the user lies flat on their stomach and steering is controlled by a weight shift on the elbows.

Introduction

We met with Melissa Draper for the motorized scooter board project. This device will be used by numerous disabled children, but needs to be designed to the specs of one child in particular. We did not get to meet with him as he was absent but we got to sit in on a child who was similar to him in condition. They have impaired strength in their shoulders, thus the whole motivation behind this scooterboard is to help with the children’s sensory impairment and to build up strength in their upper body.

The scooter needs to support around 60 lbs. It needs to be around 5 feet long and at least 16 inches wide. The scooter needs to have some type of harness to secure the child on the device because of their lack of upper body strength to hold them on the scooter. Mrs. Draper requested that the therapist have control of the speed of the scooter rather than the children. It needs to be designed so that the child’s weight shift on his elbows controls the steering ideally while laying flat on their stomach. The child we set in could apply approximately 40 lbs through his elbow on a weight shift. It needs to be low speed for the safety of the children.

Design Specifications

The scooter board should be about 5 ft long and at least 16 inches wide. It needs to be able to hold a capacity of about 60 lbs. It needs to be designed so that the forearms are to be parallel to each other. Safety is of paramount importance since the children are unable to protect themselves from falls. A small electric motor would suffice for the low speeds in which the therapists desire it to travel. The turning radius needs to be such that the children can maneuver through cones and different courses. The wheel base should be wide for the safety of the children. Ideally the motor would be able to be controlled with a remote.

Design Concepts

We have developed three different designs for this project. The first is motivated by the design of a toy known as the Rip Stik, which is similar to a skateboard but uses caster wheels and a center pivot instead of trucks. The second design utilizes a mechanical lever and pulley system controlled by the elbows. The third uses force sensing pads to drive an actuator to control the steering. All are three wheeled, flat board designs (one in front, two in back). All use a rear-wheel drive chassis powered by a small electric motor, which would be controlled by the therapist either remotely or through a tethered control box.

Design Concept 1

This design is inspired by the Rip Stik, which is a type of skateboard that uses caster wheels in conjunction with an axially twisting board. These images show our inspiration, the Rip Stik, followed by a hand drawn picture of our design, then by a top and rear view drawing rendered in AutoCAD. This scooter will be powered by an electric motor with a chain and two sprockets to drive the rear wheels, and is steered by shifting one's weight to twist the front half of the board and thus turn the caster wheel.

PROS

  • Twists in the center- no complicated mechanisms
  • Side rails for safety (as well as safety harness)
  • Intuitive steering

CONS

  • Possible difficulty in returning to neutral if it twists too far (spring assisted return?)
  • May be targeting abdominal muscles more than shoulders and arms
  • Twisting in the center may not be comfortable if twist is significant (padding for the gap)

Design Concept 2

This is a hand drawn design of a different concept. Unlike the first, it uses a single flat piece for the board, instead utilizing a mechanical system of levers and pulleys for steering. Pushing on the levers with the elbows turns the board.

PROS

  • Single board- stability
  • Intuitive turning- lean the direction you want to turn
  • Relatively simple mechanism with 1:1 input

CONS

  • Pulley system could break or come apart (utilize channels for cabling)
  • Force required may be too great for the children
  • Applying force to push one lever down will pull the other lever up in response

Design Concept 3

Our third design utilizes a single flat board as well, but instead force sensors are used to measure the child's input. These sensors then drive an actuator to turn the front wheel.

PROS

  • Input could be adjustable to the child's needs
  • Can handle of wide variety of children of different ability
  • Easier to shift weight back to neutral

CONS

  • More power hungry
  • Possible difficulty in wiring
  • No force feedback from the sensor

Concept Evaluation

Design Overview

For our final design decision, we made a chart and graded our three designs based off of parameters we deemed important for the design.

DesignChart.jpg

Our final design is an optimization of our first design based off of the Ripstik. It is the simplest design out of the three, and has the potential to produce the best final product before the delivery deadline. What is shown here is the core of the overall design; this is the minimum we have set for the design in order to ensure delivery of a finished product on time. There are additional modifications and special features we would like to include if possible, and we would appreciate any input you can provide on how to implement these features.

DESIGN FEATURES

  • Torsion spring for assisted return to neutral position
  • Single center-mounted drive wheel, tether controlled with onboard emergency kill switch
  • Flexonite wheels for grip on smooth indoor surfaces
  • Battery powered (power wheels batteries last 1-3 hours)
  • Large board body with variety of removable foam bolsters to accommodate a large range of different children

DESIGN ELEMENTS TO BE INCORPORATED IF TIME ALLOWS

  • Remote Control Operation (for therapist)
  • Variable Speed (Hi: 4mph, Low: 2mph, Off, Reverse)

Engineering analysis 1

Motor analysis. With a desired maximum speed of 4mph, our calculations show we need a 0.1303 hp motor to power the scooter.
flickr:5577930373

We found a suitable motor for our purposes, but did not realize that it was an air motor until 2 hours ago.

Engineering analysis 2

Front caster wheel assembly simple force analysis.
img004.jpg

Engineering analysis 3

Torsion spring analysis. We calculated a spring constant for the torsion spring in the event we decided to fabricate the support bar ourselves. Our design currently calls for an off the shelf replacement Ripstik torsion bar for ease.
flickr:5578513630

Unforeseen Developments

We had chosen a motor for our design based off of our calculations in the analysis, but we did not realize that it was an air motor until much later. We have decided to adapt the motor/gearbox combination out of a Power Wheels Jeep to drive our board.

Bill of Materials

Part Origin Part # Price ($)
Rip Stick Torsion Bar Online W15055099194 20.00
3 Caster Wheels Online T9AB355343 50.00
4'x8' Sheet of Plywood Lowe's unknown 30.00
10' 2x6 Lowe's unknown 10.00
Foam Pad 1.5" Hobby Lobby unknown 25.00
Velcro Hobby Lobby unknown 10.00
Vinyl Fabric Hobby Lobby unknown 15.00
Drivetrain Wheel Online unknown unknown
Paint/ Misc. Hardware Lowe's unknown $40
Power Wheels Jeep* Walmart N1476 200.00
Total Price est. $450-500

UPDATED 4/8/11 Bill of Materials

Qty Part Source Part # Price ($)
1 4'x8'x0.75" Birch Hardwood Plywood www.lowes.com R12271 44.97
2 10' 2x6 www.lowes.com LBR-31100 9.90
3 5/16" lag screws 4-pack www.lowes.com 881823 19.86
1 drywall screws www.lowes.com 35038 4.58
1 Poly Foam Pad 2"x27"x76" shop.hobbylobby.com 652289 27.99
2 Poly Foam Pad 3"x22"x22" shop.hobbylobby.com 652362 21.98
1 Industrial Strength Velcro Roll 2"x15' www.amazon.com VEK90197 23.01
1 Rust-Oleum Metallic Silver Spray Paint www.amazon.com 1915830 6.99
4yds Expanded Vinyl- Ranger Pacific Blue warehousefabricsinc.com RAR9PAE 39.92
1 Power Wheels Jeep www.walmart.com N1476 199.00
1 Rip Stick DLX Replacement Torsion Bar shop.ripstik.com W15055099194 19.99
3 Caster Wheels www.globalindustrial.com WBB355342 45.75
- Rubber membrane Undecided Undecided -
- Drive Wheel Undecided Undecided -
1 Variable Speed Remote Controller/Receiver Justin Unknown -
Total Price $463.94*

*All items found online for ease of ordering. Shipping prices/sales tax are not accounted for in estimate. Walmart and Lowe's offer free shipping for in-store pickup.

Part Drawings

Ripstik Replacement Torsion Bar

flickr:5577769009

Assembly Instructions

Include as many descriptive pictures as possible.

Implemented Design

Include pictures of the final product.

Summary and Conclusions