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From: Joe Gwinn <joegwinn@comcast.net>
Newsgroups: sci.electronics.design
Subject: Re: like butta
Date: Sun, 26 Jan 2025 20:23:02 -0500
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On Sun, 26 Jan 2025 23:52:23 -0000 (UTC), Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

>KevinJ93 <kevin_es@whitedigs.com> wrote:
>> On 1/25/25 8:22 AM, Phil Hobbs wrote:
>>> Glen Walpert <nospam@null.void> wrote:
>>>> On Thu, 23 Jan 2025 03:43:03 -0000 (UTC), Phil Hobbs wrote:
>>>> 
>>>>> Simon and I are working on a TDR based soil moisture sensor for
>>>>> agriculture.  Like many such things, it uses two parallel tines made of
>>>>> 18/8 stainless, that form a balanced transmission line.
>>>>> 
>>>>> Ours has a slide hammer for pounding it into really difficult soil, e.g.
>>>>> hardpan. The measured shock from that is around 1.6E5 m/s**2, i.e. 16000
>>>>> gees, and over its lifetime it might see around 1E6 blows. Challenging.
>>>> 
>>>> Have you considered using a mechanical low pass filter on your slide
>>>> hammer, a pad on either the hammer or anvil striking surfaces?  Rawhide
>>>> faced iron hammers are very good at driving stakes into very hard soil
>>>> without the severe impulse of a metal on metal impact, and while rawhide
>>>> might not be good for 1E6 cycles you could try rubber sheet or heavy
>>>> gasket material, tune the response by changing thickness and hardness to
>>>> suit.  Presumably the same slide hammer is used for removal, so you would
>>>> want to pad the upper surface also.
>>>> 
>>>> Between padding the hammer and compliant mounting of your circuit (two
>>>> series low pass filters) you should be able to keep the acceleration of
>>>> your circuit module to something reasonable.
>>>> 
>>>> Hard epoxy potting compounds can put a lot of stress on parts from
>>>> differential thermal expansion, sometimes a compliant layer of a more
>>>> flexible material is used over sensitive components before potting with
>>>> hard epoxy.
>>>> 
>>>> Glen
>>>> 
>>> Thanks, that’s interesting.
>>> We’ve thought about a pad, but haven’t done any studies yet. The problem of
>>> hard epoxy ripping things apart is pretty well known, I think—as you say,
>>> the fix is a thin layer of RTV or something like that.
>>> 
>>> I didn’t know about rawhide-faced hammers, which sound cool. 

Rawhide faced iron hammers would certainly work.

>>> With hard
>>> materials, the pulse width equals the length of the impactor divided by the
>>> speed of sound in the material, which in this case is just about 20us.  The
>>> force is the change of momentum divided by the pulse width.
>>> 
>>> If the pad compresses by 1 mm when the slide hammer arrives at 2 m/s, the
>>> pulse width is about 500us, so the peak acceleration would be more like
>>> 1000 gees.
>>> 
>>> Cheers
>>> 
>>> Phil Hobbs
>>> 
>>> 
>> 
>> There are also "Dead-Blow Hammers" used for automotive bodywork. They 
>> spread the strike over a longer period, often by being hollow and filled 
>> with steel shot.
>> 
>>< https://en.wikipedia.org/wiki/Dead-blow_hammer>

These are too soft to drive a steel rod.

>> 
>> kw
>> 
>
>I had one of those back at IBM.  They seem a bit on the wimpy side for
>pounding stakes into hardpan, no?

Not to worry, help is coming ...

..<https://youtu.be/eIw3uNCDR_s>

..<https://youtu.be/XWv2EvzwycM>


There are smaller options.

..<https://rohrermfg.com/brands/Man-Saver-Post-Driver.html>

Joe