[Milsurplus] Dynamotor curiosity

[Michael Hanz]

The AN/ARR-15 does not have the four small Lord dynamotor shocks that 
the command set receivers have.  It only has four snap slide posts 
riveted to the chassis.  That means they had to put rubber shocks 
between the snap slide mounting plate and the dynamotor body.  So they 
cemented four small square pieces of 3/8" thick rubber between eight 
tiny stainless steel 3/8" square pads with #8-32 x .200" threads on 
them.  See closeup photo below (the spring straps are static grounding 
links from the dyno body to the mounting plate).  The PE-86 dynamotor 
used for the venerable BC-347 interphone amplifier installed in 
thousands of USAAF aircraft during the war used the same design 
approach, and had the same problem of delamination of the rubber from 
the little stainless pads.  Rubber adhesives just weren't quite up to 
the task back then.



These dynos appear to be second generation, judging by the 1951 and 1952 
contract dates on the DY-34 label and 1945 contract dates on the DM-53.  
The first generation was produced in 1945, but I suspect they were made 
the same way.  The Collins engineers evidently wanted to use a lower B+ 
voltage (220vdc) à la BC-348, but needed the smaller footprint of the 
250vdc command set dynamotors.  This seems to be an expedient that was 
the easiest and less expensive to produce.  It _does_ present a 
curiosity, looking back from the present day.

BTW, yesterday I optimistically assumed that the command receiver dyno 
mounting plates had the same snap slide hole pattern and might be easily 
used as a replacement on a partial DY-34B like the one in the auction.  
So much for hope....the hole pattern is 2.750" x 2.000" on the command 
receivers and 2.750" x 1.625"(asymmetric, as you can see above) on the 
ARR-15.  Darn!  Close but no cigar...

          73,
- Mike  KC4TOS

On 3/19/2020 12:19 AM, Robert Downs via Milsurplus wrote:
>
> My only comment is that looking at the photo and the rest of his ad, 
> it’s pretty obvious that the seller doesn’t know his market. 
> DY-34B/ARR-15 would get if nothing else a lot more hits than DM-53.  
> And it is, after all, no longer usable as a DM-53 other than for parts.
>
> But I have never seen a complete DY-34.  What are these rubber pads 
> mentioned by Mike H?
>
> Robert Downs
>
> *From:*milsurplus-bounces at mailman.qth.net 
> [mailto:milsurplus-bounces at mailman.qth.net] *On Behalf Of *Michael Hanz
> *Sent:* Wednesday, March 18, 2020 12:10
> *To:* Jack Antonio; milsurplus at mailman.qth.net
> *Subject:* Re: [Milsurplus] Dynamotor curiosity
>
> Looking at the dyno photos, that's the way it was originally made, 
> Jack.  See photo below on one of mine.
>
> It's a pity the snap slide base with the four rubber pads is gone, but 
> those small rubber pads are forever prone to detachment over time.  I 
> do have a couple of spare "command set" dyno snap slide baseplates if 
> anyone needs one for an application like this.  I'll even bore out the 
> hole in the middle, for postage.  Rubber pads not included, but you 
> can get the rubber at McMaster-Carr and use a razor blade to cut them 
> out.  That will still leave the eight small metal end plates to 
> fabricate, but that wouldn't be too hard on a lathe.
>
> - Mike  KC4TOS
>

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