ANT Forum

Hi,

I am looking at the "Bike Power Device Profile" and I don't understand if an Ant+ display device (like Garmin 705) can calculate the power value from a crank torque sensor and a separate cadence sensor (obviously both of them Ant+).

Doing so the torque sensor will send only the "accumulated torque" value (with "crank ticks" = 0, "istantaneous cadence" = OxFF, "accumulated crank period" = 0) and the display unit will receive the remaining parameters from the cadence sensor.

Is it possibile?

Thanks,

Marco      

I don't really understand why you ask that.
Crank torque sensors send cadence information, as they are physically attached to the crank/bottom bracket and measuring and sending cadence is a trifle for them.

Is there a particular use case behind your question?      

I'd like to know if a display device can calculate the power value reading the torque from a torque sensor and the cadence from a cadence sensor.
In this case the display device will calculate the power value using data from two different sensors.

Thanks,

marco      

Since haven't received any answer, I pose my request again.

We are developing a bike torque sensor which communicate with Ant+ standard display devices.

We doubt the Ant+ protocol allows to calculate power from torque and cadence receveid from two different devices (our torque sensor and a common Ant+ cadence sensor).

In this case I could mount on a bike my torque sensor, an Ant+ standard cadence sensor and an Ant+ standard display device has to do the computation.

It seems to me that this case isn't pointed out in the Profile Guide..

Can anyone help me?

Thanks,

Marco      

The way I read the spec for the Standard Crank Torque Main Data Page (0x12) the Accumulated crank period field is not optional you have to provide it. So if you are making a crank torque sensor you need to have suitable hardware for this.

With the code I have in IpBike (still beta and I have not had access to a crank torque device to test with so probobly bugy for that) what you want will not work at the moment. I would be suprised if you could find a head unit which would work this way.      

If I remember right, the Bike Power device profile REQUIRES the sensor to send power - torque, speed, cadence are optional.

The Bike Power profile does NOT require ANT+ displays to calculate power from torque and cadence. So you can expect that currently available ANT+ displays (Garmin, iBike, ...) will not do this.

Besides, I wouldn't expect that power values calculated from torque and cadence retrieved from physically disjoint sensors are very exact, because the two sensors sample and transmit with different rates and time lags.