RE: Hydraulic Drive

["Steve Tyng" <stevet-at-stcharlesmd.com>]

Frank wrote:

> If anyone out there knows something about hydraulics, please
> give me your opinion on the use of a hydraulic pump (driven
> by an EV Warrior) to drive hydraulic motors that drive the
> tracks and cylinders that control elevate and rotate.

I studied and maintained hydraulic systems in the Navy.

Given the same power source (a battery) a hydraulic vehicle will be heaver and less 
efficient, more complex, and more expensive than the equivalent mechanical 
transmission vehicle.  My reasoning,

Heaver and less efficient:

You are replacing a relatively lightweight and efficient gear or belt/chain 
reduction with one hydraulic pump, two hydraulic motors, a reservoir, associated 
piping and hydraulic fluid, and of course the control valves.  There is a lot of 
reciprocating and internal frictional losses in an hydraulic system as compared to a 
well conceived roller chain or gear reduction.  At rest, a hydraulic vehicles motor 
is still running, pumping fluid through a loop and wasting battery power.

Complex:

A hydraulic system will not reduce the amount of control electronics or wiring.  
Instead of controlling the direction/speed of motors your controllers/servos will 
now be controlling hydraulic directional control valves.  Hydraulic piping will be 
harder to route than electric wiring.  Every pipe fitting is a potential leak point. 
 Hydraulics does reduce the number of electric motors required but to get the same 
power output will require a motor more than twice as powerful as the two it replaced.

More expensive:

Hydraulic components in the size range required for 1:6 scale vehicles are not your 
standard surplus store item.  Log splitter components are just going to be to big.  
I priced a small hydraulic motor suitable for a tank drive motor at $88.  For that 
price four EV Warriors can be purchased.  I haven't looked for miniature control 
valves but I can't imagine they would be less expensive than a 40 amp reversing 
relay.

Hydraulics start to make sense when your limited to one non-reversible power source 
and your vehicle has multiple reversing rotary and reciprocating motion 
requirements.  A bulldozer is a good example or a gas powered tank if it were 
allowed by the rules.

Just my two cents worth.

Steve "I'd build hydraulic for the challenge" Tyng