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STAC ZERO: Troubleshoot speed and power readings

  • Updated

How do I get an accurate speed reading?

To ensure you're getting an accurate speed reading,

  1. Make sure your spoke magnet and speed sensor are aligned. The red light should blink (Halcyon) or toggle on/off (Powermeter) on every wheel rotation.
  2. Update your brake rim circumference in STAC Control Panel if your wheel is smaller than 700c (or 29" MTB). 

That's it! Your wheel speed is equivalent to Distance (# of wheel rotations x circumference of the brake rim) over Time. 

As long as your trainer can detect each wheel rotation and knows the rim circumference, you have the correct speed reading for the purpose of your power calculation. 

Find out why this is different from your speed on the bike.

 

My speed my AND power readings are all over the place!

If your speed sensor doesn't pick up the spoke magnet on every wheel rotation your reported Speed and Power can randomly drop to 1/2 or 1/3 of what they should be. This can also come with other unpleasant symptoms, such as Bluetooth dropouts. 

If this happens troubleshoot the spoke magnet placement. 

Keep in mind that if your Speed reading is wrong, your Power reading must also be wrong. If your Power readings seem reasonable, read the next couple sections to understand why a "weird" speed reading on its own isn't necessarily a concern. 

If you stop getting updated Speed/Power readings in your training app, or your avatar stops moving in Sim mode, troubleshoot your Bluetooth Connection. 

My speed is different from my outdoor speed on the bike

My speed is different from another speed and cadence sensor

 

The Trainer's speed value is off by a factor of 3.6

Some very early firmware versions had a bug where speed was reported to apps incorrectly over Bluetooth. (Someone put a an imperial input in a metric field. Oops!)

Since the speed used to calculate power, the power reported to apps, and the virtual speed calculated by your app are all accurate in these versions, we don't think it's essential (given the role speed plays in indoor training), but if it bugs you, you can fix it by updating the firmware to on your Halcyon. 

 

Cadence

The STAC Zero Halcyon is capable of detecting cadence in Erg mode, but you will require a separate dedicated cadence detector if you want a cadence reading in Sim mode.

To detect cadence in Erg mode:

  1. Open STAC Control Panel and connect to the trainer
  2. Select Halcyon Tweaks, and scroll down to Erg Mode Cadence Detection.
  3. Update the Big Ring Teeth and Small Ring Teeth fields to match the number of chain teeth there are in the gears you will be using in Erg Mode. We recommend using your fastest gear. On a typical road bike, these are 50 (big ring) and 12 (small ring).
  4. Use the toggle button labelled Enable/Disable Erg Cadence Detection.You should now see a cadence reading when you use other apps in Erg Mode. You can see your cadence in STAC Control Panel from the Logging menu, and on the Erg Mode Cadence Detection

To detect cadence in Sim mode:

Install a separate cadence detector (available for purchase as an accessory from www.staczero.com). Most training apps are capable of connecting to the Halcyon and a separate cadence detector via BLE or ANT + simultaneously, and displaying data from both. The steps to change the source of your app’s cadence reading from the Halcyon to your cadence detector may differ between individual apps. Consult the app’s support.

STAC Control Panel does not currently support two devices over BLE or ANT+, and therefore cannot display cadence data in when in Sim mode. This may change in future updates.

 powermeter

The STAC Zero Powermeter supports automatic cadence detection, and should give you an approximate detected cadence while you're riding.  Note that if you have a dedicated cadence sensor, we recommend using that while using riding software on your sportswatch, phone, PC, or Mac because our cadence value will be an approximation.

 

How does it work?

Much like detecting the pitch of a music note, we analyze the varying force on the magnet array as your wheelspeed varies during your pedal stroke.  If you have a really smooth pedal stroke, the cadence readings might vary quite a bit, as the wheelspeed variation we depend on to do the calculation may disappear.

 

 

My Powermeter Readings are Jumpy or Shaky

A bit of jumpiness in powermeter readings is somewhat expected: The STAC Zero powermeter samples your power up to four times per second, which means some samples will include your power stroke, and some will include your deadzone when your feet are coming over the top of the pedal at 12-and-6.  This "natural" shakiness shouldn't be too extreme however. 

There occasionally can be causes of jumpier readings, and the ones we know about are listed below.

  1. Make sure that your spoke magnet is getting picked up by the magnet sensor on every single wheel revolution.  If it misses a single revolution, that will result in a power reading approximately half of your previous one.  If it misses two revolutions, you'll see a power reading about 1/3rd.  See the spoke magnet article for tips on spoke magnet placement.
    • TIP: You can tell if the STAC Zero sees your magnet by the red light turning on or off each time the magnet goes by.
  2. Make sure that there's nothing touching your resistance unit (magnets and calipers) that isn't the trainer frame.  If there are wires or objects on the floor that the resistance unit is resting on, that can cause wildly changing readings, since it means your body weight might be getting transferred to the force sensor, and be misinterpreted as force.
  3. Make sure you don't have TWO magnets getting picked up by the powermeter.  This can result in powermeter readings twice as large as the "true" value.  If you have two devices on your wheel that require spoke magnets, the STAC Zero should work just fine with the other device's magnet.  See the spoke magnet article for tips on spoke magnet placement.
    • TIP: You can tell if the STAC Zero sees your magnet by the red light turning on or off each time the magnet goes by.

  4. Powermeter shows 0W during a ride

If your powermeter shows 0W during a ride, it typically means that your spoke magnet or speed sensor stick have shifted slightly.  Sometimes your spoke magnet slides down its spoke while your wheel is spinning quickly.

Ensure that your speed sensor is correctly picking up your spoke magnet.  Move the speed sensor closer, with its tip close to the spoke magnet.

powermeter-wheelsensor-working.gif.gifpowermeter-wheelsensor-not-working.gif

If that doesn't resolve your issue, try the spoke magnet troubleshooting article for tips to fix this problem.

 

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