DIY Shock: Rubber vs Hydraulic Damping + Information Help 1

[ChrisDanger]

I'm helping a friend design a coilover shock for a wheelchair for his nephew. He suggested using an o-ring or seal friction damper, but after not finding much information to aid in design I wondered if using hydraulics would be viable, but I couldn't find much information on that either. I'm wondering two things: Which would be cheaper in the long term, and where can I find information about design details? He works in a machine shop and will be fabricating everything himself.

The way I see it, a rubber damper might suffer from wear and need friction elements replaced fairly frequently (also giving a declining performance), whereas the hydraulic damper might be (slightly?) more expensive to produce but last longer between maintenance schedules (and give more uniform performance over time).

Both designs have stumbling blocks. I can't find any guidelines on gland dimensions, seal material, or required surface finish for any friction dampers. And for the hydraulic shock how is oil inserted and topped up? I imagine some kind of valve but again, I couldn't find any information on this either.

Preliminary designs are below for reference.

Elastomeric:

Hydraulic:

 

[ChrisDanger]

Thanks Greg. Good to know.

 

[GregLocock]

Bear in mind that all the energy burnt in the shock absorbers has to be supplied by your power source. Human powered vehicles are very sensitive to this.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?

 

[LittleInch]

Have you come across these guys

http://www.suspa.com/uk/sectors/medical-laboratory/wheelchairs/

Maybe take a peek at a truck drivers chair to see what they use.

Also these guys. They do custom units.

http://timbren.com/aeon-springs/

Depends on what your deflection and load requirements are.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[BUGGAR]

I agree with Greg. Bump energy is essentially absorbed by a reaction provided by the user. Springs reflect more force reaction to a given bumps than good hydraulic dampers. Has this been engineered yet?

I've got a write up on this from my Ariel Atom post that I will add.