DPRG mailing list archives: [DPRG] Does anyone have any experience with "servo savers"?

Wed Dec 12 13:53:57 CST 2007

Ed,

I used one form of a servo saver on an RC model car decades ago that  
sounds a little different from your spring-style saver.  The servo  
saver I used was simply a nylon cylinder bushing with about 1/10th of  
the material removed to make it 'C'-shaped.  The servo head inserted  
into the saver and had a tab that fit into the cutout.  The push-pull  
arm also fit into the saver and had a tab that fit into the cutout.   
The idea being that if the push-pull arm is stuck, then the servo can  
still turn and the servo saver flexes (the C shape opens up wider).

The servo saver I describe only tolerates 10-20 degrees of flex;  
which sounds like it might be less than a spring-style servo saver.

I'm interested in what you find out because I am studying whegs  
(wheel-legs) which require a series elastic coupling to the motor.

!!Dean

On Dec 12, 2007, at 13:29 , Ed Paradis wrote:

> Hi everyone,
>
> I was looking up servos for yet-another-robot project, and I saw some
> items called "servo savers".  They seem to be springs that dampen
> shocks to your servos.
>
> I am interested in building series elastic actuators, and if these
> things work like I think they do, they're a really simple way of
> implementing a series elastic motor.
>
> The idea in a series elastic motor (simply)  is that your motor drives
> a spring, which then drives your load, be it wheels or levers.
>
>> From what I can find online, thats exactly what these servo savers
> could do.  They seem to be more to protect your servo if a crash tries
> to back drive your servo by compressing a spring.  The energy of the
> shock goes into compressing the spring instead of cracking a gear in
> your servo.
>
> With a properly rated spring (probably one with a much lower spring
> constant than typical for these things), you could have a great series
> elastic motor that is available ''off the shelf''.
>
> Has anyone seen one of these in person?  Does this seem possible?
>
> Ed
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