Team Trike 12

List of group members:
Scott Williams
Matt Blaylock
Ben Stevens
Enes Uzel
Ben Klages


Design a mechanism to help teach a child to crawl.


On February 2nd we left to meet a 11 month-old girl with Spina Bifida. Due to her condition she has little to no use of her legs and her body size closer resembles that of a 5 month-old. Thus a hand-powered trike would have been impossible for her to operate until near the age of 3 or 4. However, the Physical Therapist suggested building a crawler. After watching the young girl, with assistance, inch her way across the floor we were all convinced that it would be something productive for her to own. This will help teach her to crawl, as well as improve her overall body control and hopefully improve her lifestyle in general.

Design Specifications

1. Safety - Crawler must be easy for child to be placed into and move about without causing harm.
2. Adjustable - The harness should be allowed to move up and down to compensate for her growth.
3. Comfort - One issue was that the crawler she tried would rub her face, we either need a different support system or softer padding.
4. Efficient - This crawler should be designed to ease friction on wheels and make it easy for her to move across the floor.
5. Affordable - The components we use must be sufficient enough so that there are no worries on safety but cost effective.
6. Appealing - This is a small girl, so the crawler should look desirable and something the parents can be proud to show to others.

Shoulder - 16 cm
Top Length - 17 cm
Arm Length - 22 cm
Hip to Knee - 18 cm


Design Concepts

Our designs range from:

  • the use of 3 wheels or 4 wheels
  • a collapsible frame for ease of storage
  • rotatable top to allow a 360 degree range of motion
  • softer padding on harness to ease skin irritation
  • Detachable handles


  • After studying the original we decided to create 3 different design concepts simply modifying from the initial crawler.
  • The harness used below is designed specifically for crawlers therefore we will not be modifying the harness but how it is attached.
flickr:6989019501 flickr:6986087173

Design Concept 1

  • Original Crawler (We know it works and can modify for specialization)
  • Fixed frame with swivel wheels

Design Concept 2

  • Still uses the 4-wheel base like the original crawler
  • Rotatable top for an increase in manuverability
  • Possibly a wider frame to ensure no contact points with child
flickr:6847711479 flickr:6847711381
flickr:6847711533 flickr:6847711429

Design Concept 3

  • 3-wheel base
  • Static frame like that of the original
flickr:6847666083 flickr:6847666061
This design allows the child to have more freedom of movement and a more compact design. The drawbacks are the lack of handle bars or a seat for the parents to lay on while helping the chid.

Design Concept 4

  • Combination of all of the above
  • 3-wheel base
  • Rotatable top

Concept Evaluation

Rated 4-1; worst to best
Consideration Design 1 Design 2 Design 3 Design 4
Ease of Use: 4 3 2 1
Cost: 2 4 1 3
Weight: 3 4 1 2
Motion/Manuv. 4 2 3 1
Ease of Construction: 1 4 2 3
Appeal: 4 2 3 1
Total 18 19 12 11

After much brain-storming, discussion, and including the results shown above the consensus is to proceed with Design 4.

Design Overview

After meeting for the preliminary design review we spent some time revisiting ideas such as the rotatable harness system and 3-wheel design. The following analysis is considering the stress distribution along the curved beam (legs), the stresses being produced when looking at the entire mechanism, and lastly determining the radius from the central point to the wheels. This was a key analysis point because we needed to be certain with the rotatable harness support system that Lauren would not be able to rotate into a strut.

flickr:6986277529 flickr:6840158216 flickr:6840158144

Engineering Analysis

  • On only the curved beam, assuming it is a solid bar.

Bill of Materials

Part Supplier Quantity Cost
7/8 OD, 1/16T GALVANIZED STEEL TUBE LOWES 2 length (10ft ea.) $ 8.90
SVIVEL GRY WHEEL , ITEM# 235528, MODEL# 4031399LG LOWES 3 $ 17.94
2.5" High Profile Aluminum Push Pins McMaster-Carr 3 $ 57.81
2"x3"x6" Multipurpose Aluminum (Alloy 6061) Block McMaster-Carr 1 $ 29.41
.5"x12"x12" Multipurpose Aluminum (Alloy 6061) Thick Sheet McMaster-Carr 1 $ 40.21
2" OD 7/8" ID (Double Sealed) Steel Ball Bearing McMaster-Carr 1 $ 16.44
1 3/8" OD 7/8" ID Steel Thrust Ball Bearing McMaster-Carr 1 $ 5.67
Steel Plate for Harness Attachment 1 WAITING ON QUOTE
Grey Genuine Sheepskin Seat Belt Shoulder Pad Cover - Pair Amazon 1 $ 24.93
Total Cost: $ 326.31

Part Drawings

  • Steel Plate for Harness Attachment
flickr:6986371331 flickr:6986475559
  • Aluminum Joint to be used instead of fabricated steel Wye Joint. [For leg and bearing attachment (top, smaller, holes used for pinning legs)]

Assembly Instructions


Implemented Design


Summary and Conclusions