【Meet friends by disassembling】Disassembling a bicycle power meter

jj1989

【Meet friends by disassembling】Disassembling a bicycle power meter [Copy link]

 

ForewordI haven't participated in forum activities for a long time. Recently, I have something to disassemble. It happened to be a forum activity, so I disassembled it to meet friends. The object of this disassembly is the stage bicycle crank power meter. Just by listening to the name, you should know what it does, which is to measure the output power when a person rides a bicycle. This cyclist should all know it. This is one of the necessary equipment for amateurs to professionals. This power meter is used by the SKY team. Let's not talk nonsense, let's look at the pictures. ###Disassembly Let's take a look at the appearance before disassembly. The crank is Shimano R8000, and the overall workmanship is very good. The glue is inside the shell, which prolongs the glue life and there is no glue overflow. The workmanship is very good. There is a light-transmitting hole in the middle of the upper cover to indicate the operating status of the device.

Figure 1

Next, let's take a look at what it looks like after disassembly. Disassembly is very simple. You only need a utility knife to cut along the shell, and non-destructive disassembly can be achieved. What is more surprising is that the PCB inside is so large, filling the entire internal space. I thought it only occupied half of it. The antenna is also a ceramic antenna. Let's take a look at the hardware solution. The main control chip is Nordic's NRF52832, Cortex-M4F core, 512 kB FLASH, 64 kB RAM, supports BLE and ANT protocols, and can be said to have excessive performance. There are also two other chips. The silk screen on them is not clear, and it is printed with a QR code. Personally, I guess, one is an accelerometer and the other is an op amp. The rest are some resistors and capacitors. The entire hardware is very simple.

Figure 2

Let's take a closer look. What is this black thing? It turns out to be an FPC NFC antenna. This main control supports NFC and can be paired by scanning with an NFC mobile phone. However, stages officials do not seem to have opened this function, and their APP did not find related operations. It can indeed be scanned using other APPs. Below the PCB is the key part of the measurement - the strain gauge. Its working principle is to convert the deformation of the strain gauge into actual force to calculate the power. It's a pity that I forgot to take a photo of this part.

Figure 3

###To sum up the entire disassembly. In general, the hardware is very simple, there is no complicated circuit, and the key lies in the software algorithm. In addition, there is the production link. Before leaving the factory, each unit needs to be manually calibrated and calibrated, and the process is also more troublesome, so the labor cost is very high (Assemebled in USA). This may also be the reason why the price of power meters is generally higher.

xxxlzjxxx

Brother, you are really awesome. You have already started to dismantle the power meter before I even use it.

lising

xxxlzjxxx posted on 2018-7-7 14:20 Brother you are really awesome, you have already started to dismantle the power meter before I even use it

That's awesome! I don't even have one, but you already have a team

jj1989

xxxlzjxxx posted on 2018-7-7 14:20 Brother, you are really awesome. You have already started to dismantle the power meter before I even use it.

You have already practiced dual cultivation, so what else do you need a power meter?  

xxxlzjxxx

jj1989 posted on 2018-7-8 21:53 I have already practiced both, what else do I need a power meter?

I am poor.