Re: Getting old is not for sissies

On Sat, 01 Mar 2025 10:22:07 -0800, Jeff Liebermann <jeffl@cruzio.com>
wrote:

On Sat, 1 Mar 2025 07:43:22 -0600, AMuzi <am@yellowjersey.org> wrote:
>

On 2/28/2025 5:52 PM, Catrike Ryder wrote:

I was thinking about fixies just the other day on my ride and thought
maybe I could set up a fixie on the Catrike. Then I considered how
often I coast. Keeping my legs moving the whole ride is not something
I want to do.
 

>

I thought about your comment this morning.
>
While almost everything humans can imagine is possible when
time and money have no value, there's no practical
straightforward way to make a Catrike fixed gear.

>
Hardly straightforward, but certainly possible.  Remove the gears,
chain and sprockets and replace them with a hydraulic gear pump, two
hydraulic hoses, and a hydraulic motor on the wheels.  This is nothing
new.  There are motor vehicles and construction equipment that use a
hydraulic pump at the engine, T junction, and a hydraulic motor on
each wheel. 
"Hydraulic hybrid vehicle"
<https://en.wikipedia.org/wiki/Hydraulic_hybrid_vehicle>
It could also be done with a generator and motor drive, but the
efficiency would likely be horrible.
>
The nice thing about a gear pump is that it's reversible.  Want to
pedal (or ride) backwards?  No problem. 
>
Efficiency is likely to be lousy.  A low power (200 watts delivered)
small hydraulic pump can be designed for an optimistic 64% overall
efficiency (80% each for pump and motors).  That's not very good
compared to a chain driven fixie at about 95% efficiency:
<https://www.cyclingabout.com/drivetrain-efficiency-difference-speed-between-1x-2x/>
I can probably squeeze out a few more percentage points by using a
different type of positive displacement pump and motor.  The pump and
motor can probably be made from plastic, to reduce weight.  Aluminum
automobile brake line should work for hoses. 
>
One potential problem is that the volumetric efficiency of gear pumps
decrease with slower speeds and fluid flow rates.  In other words,
gear pumps don't down-scale very well:
"Useful information on External Gear Pumps"
<https://www.michael-smith-engineers.co.uk/resources/useful-info/external-gear-pumps>
>
Other than eliminating the long and noisy tricycle chain, I don't see
many other benefits for a hydraulic fixie drive system.

For me, there's no advantage of making it a fixie, but I wouldn't need
to get rid of the chain to do it. The chain path can be guided by
idlers and they're not particlarly noisy. Of course, I don't hear too
well, so what do I know?

--
C'est bon
Soloman