Saturday, June 28, 2008

Thunderbirds Are Go!

Meet Thunderbird 7:

T7 resides in the spare room, specially cleared out for the purpose.

This new "space age" home built trainer is now set up for some serious workouts. Note the cat killer of a flywheel. Fortunately I don't own a cat. There is a safety cover, it's just not on there yet.

T7 also has inbuilt position adjustability in any direction you like. So I can use it for testing other cat lovers. T7 originated in the minds of some residents of "The Shire", so you can be assured it has some magic about it.

The flywheel gives a very realistic ride. I did my first short workout on it tonight and it felt great. I was able to tap out a much higher cadence and power than on the turbo trainer. A 30-min workout with an average of 169 watts.

The fan blades replicate wind resistance and give a nice cooling breeze as well.

The crank system is an SRM power meter. My buddy Pete helped install it for me. Well actually he installed it and I watched (my definition of helping can sometimes be a bit liberal), although it's not that difficult. But installing an SRM properly requires the right tools and a calibration kit, which Pete has and I don't (well not all the tools - a good torque wrench being the main missing component).

Also note the short crank on the other side. Over time I expect to be able to lengthen the cranks I can use until I'm back to a normal length crank. Next week I get my special bike leg attachment fitted.

The SRM crank then drives a Nexus hub, with an internal 7-speed gearbox (normally built into a rear wheel for commute style bikes). The Nexus hub then runs a chain to the flywheel. This "double reduction" gearing enables the flywheel to turn at very high speeds (in the order of 600 rpm), meaning the fan blades do their job by providing increasing wind resistance with an increase in speed and the rotational intertia of the flywheel replicates the inertia of a rider rolling along at speed.

Here is the T7 flight cockpit:

Ready when you are Virgil....


DW said...

Incredible. Awesome. Neat. Jealous.

JB said...

That looks fantastic. Thanks for the inspiring blog.


Anonymous said...

Hi Alex
My name is Bruno Tiggemann and I´m a gym owner and physical education teacher here in Teutônia (BRAZIL).
Since 2006 I´m also trying to build my own indoor training bike and made some progress.
I´d like to share my experiences and maybe give you some insights about electromagnetic braking.

Fell free to write to

hippy said...

Woah.. awesome!

Unfortunately I live in a studio flat in London and barely have room for my turbo + Ribble winter bike with PowerTap.

I read most of your blog last night (Lawrence in Melbourne put me onto it ages ago) and I now want to start a power testing regime like the MAP test or 10mi TT testing.

I think perhaps I'll use the Hillingdon race circuit or Richmond Park although neither seem optimal for repeatable efforts (one being windy and the other having traffic on it).

Hopefully tonight I'll read some more of your (very useful and/or fascinating) posts and some of Rick Sterns stuff to get a testing regime sorted.


Unknown said...

Dude that is some machine do you have any measurements you would like to share im thinking of building something same for my wife.

Alex Simmons said...

Simon, I sold that unit some time ago, and no I don't have the specs available.

In any case, with more trainers such as Wahoo's Kickr becoming available with built in flywheels but with prices not in the stratosphere like Velotron and SRM ergo, I think they would be very suitable options for such applications.