Strain Gauge Research

Wednesday 2-19-09

A good day today. The sun was out and it actually felt warm for the first time this year.

Today I received approval from US Team Coach, Nathan Luce, to gather data with US Team subjects following the trials for the world championships. I’ll be at the Olympic Training Center in Chula Vista to watch trials (I have an athlete competing) and will stay for a couple extra days to gather data. April 28 is the target day.

For several weeks I’ve been thinking about the calibration process for the strain gauge. Each paddle shaft is unique and must be calibrated. That involves installing the strain gauge and then calibrating the paddle. I’ll secure the paddle to a pair of stands and then hanging weights from the shaft. The paddle will flex, causing the strain gauge to generate a current. The level of current will be unique to the amount of weight I hang from the shaft.

My plan is to place one stand at the location of the non-control hand and the other at the center of mass of the control hand side blade. Then I’ll hand the weight at the location of the control hand. I’m still sorting out strain gauge location. I prefer to attach it just above the control hand because I can easily and directly route the wires to the sending unit mounted on the shaft. Also, in this location there is less likelihood of water penetration into the strain gauge, which would interfere with the signal. I know the signal will be stronger between the center of mass of the paddle and the control hand, but then wires must be routed over the hand, if the sending unit is mounted to the shaft. I could route the wires over the hand to the sending unit, but this would involve additional wires and require some method to keep them from flopping around and annoying the paddler. Another option would be to route the wires along the paddler’s arm and town their torso and attach the sending unit to the kayak aft of the cockpit. This is a lot more complicated and would probably not work in the canoe, where there is so much more body movement forwards and backwards. So I think I’ll start off trying to locate the strain gauge just medial of the control hand.

It’s critical the stand securely hold the paddle during calibration. It also must be portable if I’m to take this system to the paddlers. For calibration stands, I’m using a standard folding roller stand common in the construction industry, and I’m not using the roller component. Harbor Freight Roller Stand #95621 is the model I’ve selected. These stands are very strong and stable; as they’re designed to hold long heavy pieces of wood for use with a table saw. Instead of using the roller head, I’m installing components that will hold the paddle securely during calibration. The stand has a folding base with a telescoping vertical component for height adjustment. This will allow a variety of paddle position for calibration – horizontal, or at an infinite number of angles.

For the stand placed at the offside hand position, I’ve attached a clamp to hold the shaft securely. This clamp is the same model we use in the Biomechanics Lab at Western Washington University to hold our motion capture cameras to the wall-mounted system - Manfrotto 035C Super Clamp is the model. On a drill press I drilled holes aligned with the clamp on the piece of the box tubing to which the clamp will be attached. To allow the screwdriver to fit through the other side of the box tubing, on a drill press I drilled holes in alignment with the clamp side holes but larger in size. This allows the screwdriver to fit through the larger holes for installation of the clamp.

I’m building a platform on which the blade will rest for the stand positioned under the center of mass of the onside blade. It’s composite fiberglass and when it’s further along, I’ll provide description and photos once it's further along.

Ideas and comments are greatly appreciated.

I’m back home and recovering from the disappointment of not completing my trip. Once I returned, I plugged back into school at Western Washington University and have been working on several projects.

1. I’ve been helping to set up the motion capture system in the Biomechanics Lab. Motion capture is a way to capture human movement into a software system where a computer model of the subject can be created to analyze mechanics. Once the model is generated, changes in position, acceleration and velocity of different parts of the model’s body can be calculated to understand the movement. We built a wall-mount system for 4 of the 7 Qualysis 240 motion capture cameras we use and have the other 3 on tripods. We’ve done a motion capture of a kayaker on a kayaking ergometer (SpeedStroke) and are now working on building the model. Model-building and analysis is being done in Visual 3D spftware.

2. I’m trying to better understand how power is applied during the kayak forward stoke. With the help of Jim Shephard from Western’s Engineering Technology department, I’ve learned how to install strain gauges on the shaft of kayak paddles.
The strain gauge will initially be just on the control hand side, just above the hand. It will be wired into a small sending unit that that transmits the data in real time to my laptop in the coach motorboat. The data is available for immediate review and feedback to the athlete and saved for study and analysis back on shore.
Now I’m building calibration stands. The stands will be used to calibrate each paddle. As all kayak paddles are unique, they must be calibrated. To do this, after installing the strain gauge to a paddle shaft, I’ll place the paddle on the calibration stands. For stands, I’m using the base of a roller stand used in the construction industry. These are portable and collapseable and very sturdy. One stand will have a small clamp to hold the shaft at the offside hand position. I’m using the same clam we used for our cameras in the biomechanics lab. The other stand will be positioned at the center of mass for the onside blade. I making a clamp from fiberglass and foam padding that will closely conform to the shape of the paddle and protect it from harm.
Once the paddle is secure in the stand, I’ll hang weights from the shaft at the position of the onside hand. The readings I get from each weight will correlate with a given amount of force resulting in flexion of the paddle shaft as measured by the strain gauge.
This system will be the basis for my thesis. My advisor is Dr. Kathy Knutsen.

3. For my Exercise Physiology class, Dr. Lorrie Brilla has generously allowed be to take the class as an independent study, as it’s not offered until next fall. This will help me finish my degree more quickly. We meet for about 1.5 hours once each week to go over the material and review projects. My class project will be a review of the physiology literature related to canoe/kayak and similar sports, and to develop a training algorithm for canoe/kayak athletic development.

And last, I am very excited that the International Canoe Federation, the world and Olympic governing body for canoe/kayak racing, has asked me to speak on my biomechanics work at their International Coaching Symposium in Warsaw, Poland. They’re flying me over the last week of February to make my presentation. Not only do I have the opportunity to share my research, I will be able to hear the other presentations and learn lots of new information from some of the top canoe/kayak researchers and coaches in the world. It’s a great opportunity.