Re: Getting old is not for sissies

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.



--
Jeff Liebermann                 jeffl@cruzio.com
PO Box 272      http://www.LearnByDestroying.com
Ben Lomond CA 95005-0272
Skype: JeffLiebermann      AE6KS    831-336-2558