Built-in sensor on the driver wheel

[lucasmpr]

Hello :D. I really liked the idea of open rowing monitor.

I have a cheap Decathlon Rower120, and inspecting some videos I see my sensors are on the driver wheel (the one that you pull from, I don't really know what it is called) and not in the flywheel.

It was a little depressing as I understand that it will not work as intended.

In your opinion Is it better that I install some new reed switches (or some kind of incremental encoder) or try to build a new physics model with this little wheel in mind?

[Abasz]

In my opinion it should work. Based on the picture I think this is connected directly to the flywheel. This should mean that it has the same motional characteristics as the flywheel (may be I am wrong though). Actually I believe its the magnetic breaking mechanism.

You could actually try to connect the picup to the Pi and enable raw data recording in the settings. Then plot that in excel to a line graph and see what it gives you. it should follow some curvature

[Gordon-Shumway2]

I would add magnets to the large flywheel and attach a reed sensor or hall sensor to one of the two pillars that hold the flywheel. I assume that the flywheel is made from iron so the magnets will stick. You could use the flywheel's three spokes to visually align three magnets at the correct distance from each other. That's what I did on my old Tunturi magnetic rower.

@abasz I believe the magnetic breaking is purely mechanical. Turning the wheel with the orange circle reduces/increases the distance between the silvery magnetic quarter-circle (to the right of the flywheel)and the flywheel. The little wheel housing might contain a spring that pulls the cord back during recovery phases. It might also contain a free-wheeling mechanism to transfer power only in one direction - it is mechanically coupled with the flywheel during drive phase but not during recovery. At least that's how it worked on my Tunturi.

[JaapvanEkris]

I woukd add magnets to the flywheel as well, that will give the best data in the end.

[Abasz]

@Abasz I believe the magnetic breaking is purely mechanical. Turning the wheel with the orange circle reduces/increases the distance between the silvery magnetic quarter-circle (to the right of the flywheel)and the flywheel. The little wheel housing might contain a spring that pulls the cord back during recovery phases. It might also contain a free-wheeling mechanism to transfer power only in one direction - it is mechanically coupled with the flywheel during drive phase but not during recovery. At least that's how it worked on my Tunturi.

Than that will not work :) orm needs the recovery's free flying for best results

[JaapvanEkris]

Than that will not work :) orm needs the recovery's free flying for best results

I agree with you that for the best results, you want to measure the flywheel behaviour. But when people aren't willing to modify the machine, they could make it work by measuring at the handle wheel (at the cost of a reduced data quality).

[JaapvanEkris]

Anny success in getting it to work?

[lucasmpr]

I've finally got some courage to open it up and see inside.

The handle wheel is one-way coupled with the flywheel, when you pull the handle it drives the flywheel, when you return the flywheel keeps spinning. So there's no way it will work as is.

I don't know where I've put my raspi, so I'm waiting for a new one to do more testing.

I bought a reed switch and some neodymium magnets to attempt the modification too.

I'm thinking I'll put the reed switch at the red circle and the magnets aligned to the 3 holding arms.

I'll share more details when everything arrives next week.

[Abasz]

I've finally got some courage to open it up and see inside.

The handle wheel is one-way coupled with the flywheel, when you pull the handle it drives the flywheel, when you return the flywheel keeps spinning. So there's no way it will work as is.

I don't know where I've put my raspi, so I'm waiting for a new one to do more testing.

I bought a reed switch and some neodymium magnets to attempt the modification too.

I'm thinking I'll put the reed switch at the red circle and the magnets aligned to the 3 holding arms.

I'll share more details when everything arrives next week.

Grate, and thanks for sharing. One note: I would start with one magnet and test a bit, since in case of multiple magnets their placement accuracy is very important so incremental increase of magnets is recommended (this is from experience :))

You can place the PI on the top of the arm for the magnet break and use some duck tape to mount it. But the length of the reed switch cable is not that important (it can be as long as a meter or two), it would have impact only on the current drawn by the the setup (longer wire means higher resistance, hence higher power consumption), but this would be negligible. So you can place the PI where ever you want provided you have a long lead wire for the reed switch.

[JaapvanEkris]

I bought a reed switch and some neodymium magnets to attempt the modification too.

I'm thinking I'll put the reed switch at the red circle and the magnets aligned to the 3 holding arms.

Sounds great! 3 magnets makes sense with your flywheel (given the three spokes). Alignment of the magnets is important, although the V1Beta version can take quite some noise as well: on the Concept 2 RowErg we see some issues with magnet placement that ORM can handle. But life becomes much easier when the magnets are placed perfectly.

I agree with @Abasz that wiring can be allowed to become quite long. On my NordicTrack the cable was 75 cm long to the switch. Never had any issues with it in the year I used it.

I'll share more details when everything arrives next week.

Great, looking forward to it. Sounds like a nice project to see the results from.