Deliberate Gecko – Prototype II Final Report: RPTC

Introduction:

Deliberate Gecko has the mission of eliminating back strain, eye fatigue and wheelchair inaccessibility from a specific job at BTCO, which is near the Cerebral Palsy Research Foundation. The strain and fatigue as well as inaccessibility comes from the current methods used in the operation. The job is to record precision measurements of a printed sheet that is on top of a large calibrated plot table. This requires the measurement taker to bend over the table with a microscope for each point that needs to be measured.

Team 1, Deliberate Gecko, has developed their second prototype of Project RPTC (to be given a cool name later) to completely mechanize the current job. The prototype was built with goal of getting closer to the finished product of a completely robotic plot table camera system. This would achieve getting rid of the back strain and eye fatigue, as well as enable wheelchair users to have equal employment. Positive benefits would also include making the methods of measurement a great deal more efficient, trading manpower for electric power.

Prototype II has built on the existing Prototype I. Prototype II’s box can move itself in either direction for both the X and Y axes. The current control system includes a thumb stick that is connected to an Arduino Uno. The box will eventually hold a microscope and or camera. It currently has a motor for Y-axis travel. It sits on square aluminum tubing that has rollers on the end. Those rollers are mounted on 3/4″ rigid conduit, which is what the frame is made from. All of the movement is done by stepper motors, pulleys and steel cable.

All parts are powered from a variable DC power supply. The control system is currently running entirely wired, with the possibility of wireless in future prototypes.

Team 1 has used the following parts in this Prototype:

  • 3/4″ rigid conduit
  • Type LB rigid conduit body
  • Rigid conduit compression connector
  • Aluminum box
  • Square aluminum tubing
  • Angled aluminum
  • Stepper motors
  • Steel cable
  • Small Pulleys
  • Large pulleys
  • Caster wheels
  • Nuts, bolts, washers, bushings, hot glue, wires, transisters, diodes, breadboards, acrylic
  • Arduino Uno
  • 2-axis thumbstick

Description:

We took Prototype I  and bolted things on.

Stuck another motor as well as some large pulleys on for X-axis travel. Connected by steel cable, same as Y-axis travel.

 That is on the end of the Y-axis rail.

 We also made a box for the control system, using a laser on acrylic glass.

It uses an Arduino Uno with a 2-axis thumbstick. To drive the Y-axis stepper motor, we have the arduino output to a column of 5 field effect transistors that supply the motor with power in a correct sequence. To drive the X-axis motor, the EasyDriver Stepper Motor Driver is used.

 

Diagrams:

After we figured out the correct sequence of the stepper motors, we had them controlled from an Arduino UNO.

One motor uses field effect transistors and the Arduino outputs, while the other uses an EasyDriver module.

The thumb stick inputs 2 different directions via varying resistances into the Arduino. 

LINK TO CODE HERE

Reflection:

More money for custom parts such as belts and motors! (Not needed for prototypes, but for end product it would be)

Also, using 80/20 extruded aluminum for the frame should be considered. A large drawback is that it is much, much heavier. The rigid conduit is currently functional and fairly inexpensive.

Using The Yard to purchase supplies and parts for our project was very helpful. We should have gone there first instead of making initial purchases at Lowes and Home Depot.

Using custom motors without documentation added a fair amount of extra work time into our project. For the 5-phase variable reluctance stepper motor, we had to manually determine the sequence of the phases, as displayed here. We should have gotten better motors that are easier to use.

With both prototypes, we built a full scale working model. This was a mistake, as it would have been much simpler and cost effective to build a small scale model. Using the full size, the motors that we acquired are not powerful enough to run in an ideal setup. They just are not fast or strong enough to move the entire length of the frame. Currently, the prototype moves, but it is not fast enough to be viable.

Do not disconnect or connect motor from EasyDriver while power is on. We may have burned through an EasyDriver module or two.