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Topic: Controlling resistance on Magnetic Exercise Bike (Read 13667 times) previous topic - next topic

mike390

I purchased a used magnetic  stationary bike and i realized the controller console was missing.  I couldnt return the unit so i decided to build my own basic console, just so I can control the resistance on the bike to make it usable.   It has a 10 wire rainbow cable going to the control panel that leads into the bike.   I cant find anything on this bike as it is a cheap chinese product. It is a JMC-4105. 

This is the only picture gallery I can find of the  unit: https://www.gcsurplus.ca/mn-eng.cfm?snc=wfsav&sc=enc-bid&scn=101149&lcn=245994&lct=L&srchtype=&lci=&str=1&ltnf=1&frmsr=1&sf=desc 

I was wondering if anyone knew how magnetic cycles worked and how the motor is usually controlled, if any one has experience with these kinds of bikes?  I know the bike uses electric currents to power the magnets to create or reduce resistance to the wheel inside.  I do not know what kind of signal (PWM or straight DC)  and the voltage/current required.

MarkT

Couldn't see any info on the web - you'll need to open up and look at / photo the innards
I think...
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mike390

I was going to do that tomorrow when I have time to crack it open, just wondering if we had anyone experienced with these units on the forums first :)

acedward

I'm  very interested in your project
I hope you can upload the pictures soon !!

Chagrin

There are a lot of ways this could be done but more than likely it's going to come down to just shorting the ends of a coil together. You'll probably just need a transistor/mosfet and a PWM signal to vary the resistance.

Don't lose hope on this one; it's a very doable project.

MarkT

I don't think so, the rotating disk isn't full of magnets, that would be
expensive, theres likely a rotating aluminium or copper disk and a magnet
set that hinges over it with some positioning servo or actuactor to vary
the degree of flux linking the disk.

http://en.wikipedia.org/wiki/File:Magnetic_resistance_stationary_bicycle_exercise_bike.JPG
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TomGeorge

Hi, the bike uses an EDDY CURRENT retarder, bigger versions are used on car and engine dynomometers, you feed the coil on the retarder with AC or possibly PWM to induce eddy currents in the aluminum disk. The current causes a braking force or retarding force.

Tom...... :)
Everything runs on smoke, let the smoke out, it stops running....

jgum

I repair fitness equipment for a living, but I do not recognize this unit. A pict of the inside will really help. But if I had to guess on how it works would be a 6 Vdc tension motor that pulls some magnets closer to a copper clad flywheel.  The tension motor are enclosed in a plastic gear box and most have 5 leads. Three for the position pot (1k?) and two for the motor. The unit will also have a reed switch for rpm sense and 2 wires for the optional external power source. ie wall xfmer. I also could be all wet on this. Hope this helps.

paulimp

i have a similar proyect, i hve to output the values the bycicle to a pc for using them later can someone help me with this?

polyglot

Agree you need to disassemble it, if only to figure the pinout.  The bikes I've worked on have the moving-magnets arrangement that produces variable eddy-current drag in a conductive disc, as per MarkT's post.

Using an electromagnet for drag is possible, but it consumes power and I think it unlikely for a cheap unit.  I could be wrong there though, as it might have a very-large-turn-count coil that is capable of producing a big H-field with simple PWM control from low voltage.

breamo808

I have a BH fitness upright bike and it is not responding to resistance change intermittently.
I have attached a photo of the motor assembly.

When it works, it is fine.
But sometimes, when I switch it on and try to change the resistance level. Nothing would happen. The motor would not buzz or move at all.

And out of interest, what does that blue trim pot do?
And also the big pot?

Would be good if I can fix up this one!

Thanks Breamo

SimonMart99

My Exercise bike is acting weird today and I need to skip my workout. I am looking for solutions to fix it on my own its already beyond its warranty service.

AngelSnail

#12
Jul 20, 2015, 10:43 am Last Edit: Sep 27, 2015, 07:52 am by AngelSnail
Magnetic resistance is more technologically advanced than the strap resistance mechanism. To create magnetic resistance, two magnets set on each side of the flywheel. When you increase the pedal resistance, the magnets move closer to the flywheel, creating tension. When you decrease the pedal resistance, the magnets move farther from the flywheel, making it easier to pedal. A bike can have either manually adjustable magnetic resistance or digitally adjustable magnetic resistance. For manual resistance, a tension knob controls the magnets via cables. For digital resistance, an electronic signal controls the magnets.


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greggillies

I repair fitness equipment for a living, but I do not recognize this unit. A pict of the inside will really help. But if I had to guess on how it works would be a 6 Vdc tension motor that pulls some magnets closer to a copper clad flywheel.  The tension motor are enclosed in a plastic gear box and most have 5 leads. Three for the position pot (1k?) and two for the motor. The unit will also have a reed switch for rpm sense and 2 wires for the optional external power source. ie wall xfmer. I also could be all wet on this. Hope this helps.
Sorry to revisit a subject over a year later, but I have a similar problem to the OP. After moving house (7 years ago), I've now lost the controller for my exercise bike. I've opened it up and as you describe, I have one  motor/servo which has 3 wires and appears to be attached to a cable which pulls the magnets closer to the wheel. There is another motor directly next to the first with just a + and - lead. I've found the RPM sensor and it's 2 cables, and also have another 2 connecting to an unknown sensor just above the motor(s) but not near the wheel.
I also have 3 wires from the DC power input.
I have mapped all the cables through to the 12 core cable which pops out of the handlebars.
My questions is, what signal(s) do I need to send to which cables to control the resistance? (i.e. what frequency, voltage, resistance, etc.) The DC input is 6v.
Initially, I'd be happy with a simple knob on the handlebars to adjust resistance. Later I'd like to get an arduino or raspberry Pi controlling it and reporting on the speed, distance, pulse, etc.
I have photos, but can't see where to add them on here.
Any info, pointers or guidance would be greatly appreciated.

greggillies

OK, so I read over this thread again and made some more progress.
The motor is just a plain DC motor. Apply power and it turns a spool which tightens the magnets, thus increasing the tension. Switch the + and - on the motor, it turns the other way and releases tension. Easy! I have that bit working, and even controlled by both a microcontroller and a pair of override buttons.
The Potentiometer (which I originally thought was a digital motor or servo) gets turned by the motor/gearbox. By reading it's resistance, it should be possible to gauge exactly where the tensioner is, and stop the motor before it breaks!
This is the bit I'm now struggling with as I can't get a meaningful reading from the Pot. I hook either side of it up to + and -, then the middle pin to my multimeter. It reads the full voltage regardless of where the tensioner is. Only time it changes is when the motor is actually running, and of course the voltage drops.
Any ideas, anyone?

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