A digital display monitor for a rowing ergometer

[Jim Flood]

If you have used a rowing machine (ergometer or erg) you will be aware of the display monitor that provides data on distance and work rate.

At present Indoor Rowing competitions (http://indoorchamps.britishrowing.org/  http://www.crash-b.org/) are limited to expensive Concept2 machines (http://www.concept2.co.uk/) - but I and others want to break this monopoly by producing a display monitor that will enable any form of rowing machine to be used for competition, including self-build ones (http://openergo.webs.com/).

As a start, I would like anyone interested to build a basic display monitor (https://dvernooy.github.io/projects/ergware/) and then to link it to a force transducer and accelerometer between the handle and the chain - and a 'phone app for the display. Anyone interested?  I'm also involved in FES rowing on ergos and on water (http://www.fesrowing.com/). Contact me if you would like more information.

Jim

[Norro]

Forgive my ignorance as a non gym person but isn't the main difference in price whether the force is provided by a fan or not?

[Jim Flood]

No there several cheap impeller fan models starting at around £150

[David Price]

Jim,

Do you envisage this to be an open source project and might there be an educational/STEM aspect?

The reason I ask is that I've just started looking at mbed and the BBC Microbit which gives you a relatively low cost IoT platform and includes Bluetooth LE to support interaction with a smartphone. I would look at pairing it with a colour LCD though for integrated monitoring. The IOT development environment, mbed, gives access to a wide range of ARM based platforms including the Nordic nRF51822 chip used in the microbit which incorporates BLE. Other members are much more knowledgeable and experienced with BLE and Nordic devices and could advise if this is a non starter.

My primary interest would be as a STEM project to help me learn the associated technologies.

David

On Monday, 16 April 2018 20:32:18 UTC+1, Jim Flood wrote:

[Richard Ibbotson]

Could you make just a wireless battery powered force measuring handle?

Easy to use on any machine and low cost. The cheap force sensors give around 80 measurements per sec

Sent via Richard's Phone

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[Andrew Jacobs]

Always happy to help out on the electronics.

The project you reference only seems to need a basic rotation sensor to work out the characteristics. Do you really need the force transducer and accelerometer?

[Andy Noyes]

To take accurate measurements you would (I think) need to know both the amount of force applied to the handle and the distance over which it is applied each stroke. You could infer the distance from the length of time the force is applied, if you know the inertia of the system, but that would vary between machines and probably wouldn't be a simple linear relationship with a fan.

What about putting the force sensors in the footrests instead of the handle? No need for wireless and the seat is on low friction rollers so the force should be equal. And a simple quadrature encoder on the chain itself, counting the links?

[Bob Dunlop]

On Tue, Apr 17 at 03:17, 'Andrew Jacobs' via Reading Hackspace wrote:
...

> The project you reference only seems to need a basic rotation sensor to
> work out the characteristics. Do you really need the force transducer and
> accelerometer?

To calculate the energy supplied in this example you need the force applied
and the distance it was applied over. A strain gauge gives you force and
the accelerometer distance by intergrating twice. You need a bit of math
to remove the effect of gravity from the accelerometer and some logic to
detect the power and recovery strokes. The system would provide a highly
reproducable measure of the energy input based on hard physics, no
dependency on the efficiency of the "wheel" which I think is what you
would need for comparative racing.

The rotational speed measurement is fine for an individual machine but the
translation to power makes all sorts of assumptions about the efficiency
of the machine. Very hard to equate measurements on one machine to another.

Actually there's a fudge factor in the accelerometer case as well. You
need to account for the mass of the handle that you are accelerating as
well, but that's also an unequivical measurement. You can even use the
strain gauge to weigh the handle by letting it hang free from the chain
before you start you excercise.

I'd invisage a Bluetooth device built into the handle with accelerometer,
and force measurement on the linkage to the chain. Your display and
recording device is then a free choice, probably phone or tablet.

I might suggest adding a three axis gyroscope alongside the accelerometer.
Make the acceleration measurement easier/more accurate during rapid
changes of orientation relative to gravity.

--
Bob Dunlop

[Andrew Jacobs]

The PM5 module used on the Concept2 has just one sensor connected to the flywheel (probably measuring the rotation -- see page 3 here http://www.concept2.co.uk/files/pdf/us/monitors/PM5_QuickStartGuide_EnglishOnly.pdf). All the other connections are for external communication.

The maths on http://dvernooy.github.io/projects/ergware shows everything can be calculated from this if you use some magic values in the calculations or perform a calibration. A magnet and a cheap hall sensor is probably all you need and will make the design simpler for makers to build.

[Richard Ibbotson]

The problem that I see with measuring rotation is that calculations or measurements must be made for each machine. Measuring force and distance over time at the handle does not need this and round be much better for fair competition.

I wasn’t sure about accelerometer due to the double integration errors, but given the reciprocating and limited motion it might be OK

Sent via Richard's Phone

On 17 Apr 2018, at 11:34, Keegan Neave <keegan...@outlook.com> wrote:

A while back I built an Arduino based speedometer for my deskcycle, it communicates with a desktop application using serial.  It's not Micro:BIT but as a similar concept some of the code may be useful:

https://neave.engineering/2015/04/03/arduino-speedometer-for-the-deskcycle/ 

[Keegan Neave]

Aye, a lot less constrained an issue than I faced for sure!

[Richard Ibbotson]

For educational or STEM, you could even compete in the classroom with a bungee cord to a bolt in the wall. Though clearly not good for real training, competition, or power delivery.

In physics or if building a proper rowing machine, a handle device could be used to calibrate that.

Sent via Richard's Phone

On 17 Apr 2018, at 14:26, Keegan Neave <keegan...@outlook.com> wrote:
Ben 

[Jim Flood]

Apologies for the delay in responding - I have been trying to sort out related areas of the overall project - which is to develop an overall package for a self-build ergo and a universal universal monitor that will enable fair competition between any type of basic rowing machine. This is to open up access to indoor rowing in poorer countries - and also to provide a platform for STEM activities in schools and colleges. What I came across very recently is: https://github.com/tijmenvangulik/Ergometerspace   My background is in mechanical engineering, so I would very much appreciate offers of help/support in putting one of these units together.

Jim 

[Jim Flood]

Many thanks for all your contributions - and again apologies for the delay in responding. I've been working with Professor Brian Andrews (http://www.fesrowing.com/fes-rowing-group/oxford-university-uk/) to develop the project - and I would like to arrange an evening meeting at RLab Brian and those of you who are interested in becoming involved.