Scrapheap Challenge - homebrew turbo trainer

[newfhouse]

Just for fun while I’m confined I’ve been thinking about constructing my own trainer from scrap that I have in my shed and garage. I don’t really want to purchase anything, even online, as it would feel like breaking my self imposed rules. I’ve fitted SPDs to my wife’s exercise machine but I’d like something a bit more bike-like. Using this for the last few days has been the least fun I’ve ever had performing repetitive leg movements.


I have plenty of slotted angle iron from an old shelf unit, so I can easily make a stand, something like this:


My first problem is that I don’t have a long skewer or any threaded rod of a small enough diameter to use instead, so can’t see a way to get the mount outside the rear mech. I think this limits me to using the single speed, which doesn’t have QR wheels.

The next decision is how to provide some (variable?) resistance. I suppose the options are some sort of roller against the tyre or possibly a chain drive to a fan or similar. The single speed has a flip flop hub so the non-drive side might work with a secondary chain.

If I opt for a friction roller I’ve thought about how I might make one. I don’t have any bearings as such but I do have a couple of old wheels from which I could take a hub. I’ve thought about potting one in some plastic waste pipe. I also have a couple of 14 inch wheels, front and rear from a child’s bike, so could just mount one on a swinging arm and use gravity or a light spring (bungee cord?) to hold it against my rear wheel.

I realise it’s all a bit Heath Robinson, but that’s part of the appeal for me. I have normal DIY tools but no welding capability.

Thoughts, ideas and flights of fancy gratefully received.

 

[Sharky]

Have you considered the older designs, where the back wheel sits on a couple of mini rollers without being clamped
The front wheel comes off and the forks are clamped to a support.

Resistance is via the gears and the rollers are oil filled (I think) go give some resistance or the really old ones had wind veins to slow it down.

If I can remember where I last saw mine, will take a photo

 

[slowmotion]

There are loads of clips on YouTube which show homemade designs for roller trainers. One used wooden rolling pins as rollers.

View: https://www.youtube.com/watch?v=gOQM3_QKgt8

 

[ColinJ]

The next decision is how to provide some (variable?) resistance. I suppose the options are some sort of roller against the tyre or possibly a chain drive to a fan or similar. The single speed has a flip flop hub so the non-drive side might work with a secondary chain.

My first turbo trainer was a fan type and it was incredibly noisy! I suppose if you used a very large diameter fan it could rotate slower and be quieter? You could also direct the airflow back onto you to keep you cool.

I'd be tempted to use magnetic braking. You'd need some very powerful magnets and a conductive disk rotating between them.

 

[classic33]

My first turbo trainer was a fan type and it was incredibly noisy! I suppose if you used a very large diameter fan it could rotate slower and be quieter? You could also direct the airflow back onto you to keep you cool.

I'd be tempted to use magnetic braking. You'd need some very powerful magnets and a conductive disk rotating between them.

Magnets from a knackered hard drive?

 

[newfhouse]

One used wooden rolling pins as rollers

There may be risk of violence if I attempt that.

 

[newfhouse]

My first turbo trainer was a fan type and it was incredibly noisy! I suppose if you used a very large diameter fan it could rotate slower and be quieter? You could also direct the airflow back onto you to keep you cool.

I'd be tempted to use magnetic braking. You'd need some very powerful magnets and a conductive disk rotating between them.

I have a broken desk fan which I was hoping to use to provide a tailwind. I expect there to be a fair amount of friction simply as a result of imprecise construction so don’t actually know how much extra I need to build in. I like the magnet idea too so will see how many I can find. I’m sure I have some penny sized neodymium ones somewhere.

 

[newfhouse]

Magnets from a knackered hard drive?

I have access to a few of those but don’t have any intuition about how many I’d need, or indeed the proximity to the rotating disc I’d require. I’ll try to build a jig and have a play tomorrow.

 

[newfhouse]

I’m sure I have some penny sized neodymium ones somewhere.

I shall try to avoid doing this, though
https://www.theguardian.com/austral...ck-up-nose-while-inventing-coronavirus-device

 

[newfhouse]

I still haven’t found my magnets to experiment with a resistance disc, but I did find a length of M4 threaded rod to use as a replacement skewer. So today I decided to make a start on building my homebrew turbo. I decided to build it around my old Secteur, which I had planned to sell about now to part fund my summer tour. Well, neither is going to happen in the foreseeable for obvious reasons.

First task was to swap the skewer for my newly discovered rod.

Then I made a couple of wooden spacers, one longer than the other to allow for the rear mech.

I made two triangular supports from some old steel shelf material...

... but realised that I would strike my heels, so reconfigured them.

A quick test run proved that it was all spinning fine. I added a magnet and sensor to the rear wheel and ran the cable to the handlebars and an old style cycle computer to monitor speed and distance. It was far too easy to pedal at an indicated 50 km/h so the next task was to add some friction. Some more shelf supports were pressed into service here to mount an old wheel in the hope that I can find a way to create resistance. The tyre is nice and wide but a bit too knobbly so runs a little noisily. I found I could adjust the inflation to get just the right amount of contact.

Well that slowed me down a bit, but not enough. I swapped the friction wheel for the rear of the pair, which allowed me to add some wooden sails attached to the freewheel. Don’t laugh, they actually work... a bit. Tomorrow I will try to add some stiff card or similar to increase the surface area and hence wind resistance.

Last construction task of the day was a support for the front wheel, to lift it a little and to lock the steering.

I needed to add another piece of shelf unit to hold it steady.

And that’s it for today. Total cost was zero pounds, I had lots of fun, and it actually works. I’ve just had 40 minutes on it, enough to raise a sweat and get the heart pumping.

 

[HLaB]

I still haven’t found my magnets to experiment with a resistance disc, but I did find a length of M4 threaded rod to use as a replacement skewer. So today I decided to make a start on building my homebrew turbo. I decided to build it around my old Secteur, which I had planned to sell about now to part fund my summer tour. Well, neither is going to happen in the foreseeable for obvious reasons.

First task was to swap the skewer for my newly discovered rod.
View attachment 512575 View attachment 512576
Then I made a couple of wooden spacers, one longer than the other to allow for the rear mech.
View attachment 512577
I made two triangular supports from some old steel shelf material...
View attachment 512578
... but realised that I would strike my heels, so reconfigured them.
View attachment 512579
A quick test run proved that it was all spinning fine. I added a magnet and sensor to the rear wheel and ran the cable to the handlebars and an old style cycle computer to monitor speed and distance. It was far too easy to pedal at an indicated 50 km/h so the next task was to add some friction. Some more shelf supports were pressed into service here to mount an old wheel in the hope that I can find a way to create resistance. The tyre is nice and wide but a bit too knobbly so runs a little noisily. I found I could adjust the inflation to get just the right amount of contact.
View attachment 512587
Well that slowed me down a bit, but not enough. I swapped the friction wheel for the rear of the pair, which allowed me to add some wooden sails attached to the freewheel. Don’t laugh, they actually work... a bit. Tomorrow I will try to add some stiff card or similar to increase the surface area and hence wind resistance.
View attachment 512591
Last construction task of the day was a support for the front wheel, to lift it a little and to lock the steering.
View attachment 512593
I needed to add another piece of shelf unit to hold it steady.
View attachment 512594
And that’s it for today. Total cost was zero pounds, I had lots of fun, and it actually works. I’ve just had 40 minutes on it, enough to raise a sweat and get the heart pumping.

View attachment 512597

Now that is a smart trainer

 

[screenman]

Does that Dexion give enough support?

 

[newfhouse]

Does that Dexion give enough support?

It‘s pretty robust. My biggest concern is whether the rod that holds the rear wheel is strong enough. I have thought about making a waste pipe roller for the bike to sit on and share the load, but without sacrificing a wheel hub I don’t have any suitable bearings.

I wish I had a fan, alternator, or similar that I could chain or belt drive, but I’m not keen to sacrifice the washing machine or lawnmower. I’m still hoping to have success with magnetic resistance.

 

[figbat]

This thread resonates with me. In the garage I have a long-unused, fan-based rowing machine. I have been mulling how I might convert it into a turbo. It currently uses a chain and single-speed freewheeling cog to run it, but the chain is a much finer gauge than a bicycle chain so I am wondering how I might fit a cycle cog to it. I have an unused 11-25T cassette I could use in whole or in part (the smaller cogs are loose). It's then just a case of working out which bike to attach to it and how to hold it upright.

The fan unit from the rowing machine is a single-resistance type with no variation. I did think that I could use the front gearing to vary resistance if I did get this thing built. If I put it on the patio near the bifold doors I could probably even use it whilst participating in a Teams call.

 

[Dogtrousers]

What a fantastic project.