ioLab Startup and Pairing
The ioLab uses a radio frequency connection to your computer. It is not Bluetooth, but uses a dongle that plugs in your usb port. The dongle resides in the back of the ioLab unit. To remove the dongle, just press down on the metal end and it will tilt up so you can grab it and take it out.
Follow the instructions for your system that are written at http;//www.iolab.science. Except for the basic start-up process, the documentation is mainly through the youtube videos. Some of the notes below derive from watching those videos.
- short press = on (less than 1 second)
- long press = off (about 2 seconds)
- if flashing alternately, then the unit is paired
- If flashing simultaneously, then the unit is unpaired
After you start the iolab application, plug in the dongle. Make sure the Dongle ID icon at the top of the application screen lights up when you plug in the dongle. Then press the start button (the right-hand one) on the top of the iolab, the side with the wheels. If the lights beside the buttons blink simultaneously, then the connection is not working. When the connection is ok, then the lights will blink alternately and you’re “paired.” The Remote 1 icon on the ioLab application should light up and say “Paired.”
The first thing you should do after you pair is to calibrate. Before you can calibrate you have to press the Start or the Reset button. Then click the Gear Icon and then …Calibrate Force. Follow the instructions that are displayed. When you do this you’ll have to turn the unit and set it on a table with y direction up. Then hang it from the force probe for a couple of seconds, holding it by the spring or bumper. The force probe caiibrates assuming that the unit’s mass is about 200 grams and that it is on earth where the gravitational field strength is g = 9.8 N/kg. I am not sure how the other sensors calibrate, but I suspect that the quantitative outputs may not be entirely accurate. (I found that the gyroscope only measures 5.4 radians when one integrates the omega of a complete 360 deg rotation, instead of 2π= 6.28 radians).
- set on the unit’s head
- hang from the force probe.
To make measurements, choose the sensors which are to be used and then start the data collection by pressing “Record.” Let it run as long as you need and then press “Stop.” The data will accumulate at the rate indicated at the top of the graph. There is no way to modify the data rate
Pairing a second remote
You can pair a second remote unit with the same dongle so that mutual forces can be measured during a collision.
- Plug in dongle and pair the first unit, if not already done.
- Turn on 2nd unit and unpair the second remote unit from its dongle if necessary.
- To unpair press the “ON” button while still holding + down for a short time (less than 1 second.)
- Keep holding the + button until the light beside the + button flashes 3 times quickly in succession.
- Now cllick on the Remote 2 on the top of the IOLab app and a dialog should appear with a button that says “Find Remote”. If the 2nd remote is flashing with a series of 3 quick flashes then it should be found
- Then choose “Pair Remote” and the second remote should be paired.
- Now both units are paired with the same dongle.
- Here’s a video on pairing 2 remotes that shows the process:
Active Learning Experiments
This series of mechanics experiments is designed to help overcome common misconceptions of beginning physics students.
- Position, velocity and acceleration: when is acceleration positive, negative and zero?
- Force and its relation to motion. Does force correlate with velocity or acceleration?
- Friction, sliding and rolling. How does one quantify friction? What factors does friction depend on?
- Momentum change and force. Impulse-momentum.
- Mutual forces during collisions
- Simple Harmonic Motion
- Torsion Pendulum: moment of inertia and effect on oscillations.
Position, Velocity and Acceleration
Make a small ramp to run the ioLab up and down on its wheels. A board is good, or even a large book could be used. Make the angle so that when you give a push on the ioLab while sitting on the ramp with its wheels down that it runs up the ramp and comes back down again.
Determine ramp slope using the accelerometer
startup and verifing calibration
Start the software, turn the ioLab on and make sure that the ioLab is correctly paired. Click the box to turn the “acceleration” sensor on. Record a few seconds of data. Check that when sitting on the table a_z is about 9.8 m/s/s. Then check that a_x and a_y is about zero/ Discepancies of around 0.02 m/s/s can be ignored, but if the variation from expected values of 9.8 m/s/s and 0 m/s/s are greater than 0.05 m/s/s then go through the calibration procedures.
The z component of acceleration will read 9.8 m/s/s when the unit is held horizontally because of the pull of gravity on the acceleration detector. The value of 9.8 m/s/s does not mean that the unit is accelerating physically, but that the sensor feels as if it were in outer space, away from any gravitational field, and is accelerating in the z direction. There is no physical way that the sensor can distinguish between a gravitational field of 9.8 N/kg and and acceleration in space of 9.8 m/s/s.
Measure a_y on ramp while cart is not moving
Reset the data — press reset once — and record one data for one second with the ioLab on the table and then on the ramp with the y direction pointing up the ramp and the wheels on top. The y component of acceleration should now be non-zero. The tilt angle of the ramp is given by θ = a_y/9.8 in radians.
Now measure the tilt with a ruler, θ=arcsine(rise/length), and compare the value from the accelerometer.
If the values you got from the two methods are very different, try to estimate whether the difference is because of the random uncertainties of the measurements, or an error in procedure. Discuss and justify your conclusion.
Record position, velocity and acceleration while moving
Now we are going to record the position, and velocity using the wheel encoder. Reset the softward by pressing reset twice. Now choose the “wheel” option in the software.
Start recording and then gently push the cart uphill. It should go up, momentarily stop and then roll back down hill. Catch the cart and then stop the recording. Below is a sample chart of that motion.
You need to display only the y components of the position, velocity and acceleration.. The zero of position is set when you start the recording. As the cart rolls up and down the ramp there is a curved line, almost parabolic When the slope of the position vs time graph is zero, notice what the velocity is. What is the acceleration when the velocity is zero? (To make the velocity graph less ugly, choose a smoothing of about 10 points.)
Look at the region of the graph where the cart is rolling freely after it leaves your hand and before you catch it. You’ll notice that the acceleration as measured by the wheel is noisy because of the surface roughness. Another thing that is interesting about the acceleration is that the value is different when it is going uphill and when it is going downhill. This change is due to friction. When the cart is going uphill the friction force is pointing downhill, helping the force of gravity to slow the cart down. When the cart is going downhill friction is in the opposite direction and retards the force of gravity that is causing the cart to speed up.
The statistics displayed on the graph pertain to the shaded area selected.
- µ: Mean value
- σ: standard deviation about the mean
- a: area between the curve and the zero axis
- s: average slope over the interval