[hpv-boats] Flex Shaft Material Selection (Dom Rumbolo)

[Rick Willoughby]

Dominic
The sewer rod is probably the better selection.  I have seen these  
rods in use and suspect they are spring steel but am not certain of  
this.  The end fittings are similar to what I have done with spring  
steel although with  5/16" diameter you do not need to be fancy if  
the connection is not seeing the bending stress.  Irrespective these  
end fittings give you something to work with for connecting to prop  
and gearbox.  So that is added value.  I have paid $60 for a single  
connector before I started making my own.

Assuming they are spring steel then you should aim to arrange with at  
least 3.5m radius curve.  For the 1.8m length you can drop 0.5m.  The  
prop shaft will need to be around 250mm below the surface so the  
gearbox cannot be any higher than 250mm above the surface.  This  
should be easily achievable with a surf ski.  The output shaft on the  
gearbox will angle down at 30 degrees.  If you can get the gearbox  
closer to the water then that is even better.  Obviously the down  
angle of the shaft will reduce in this case.

The surfski should be a good platform.  I have modelled an Epic V10  
hull to check performance and they are a slick hull.  If you have  
something similar it will go well.  You will not operate it reliably  
without stabilisers - CoG will be too high.  For smooth water  
operation you can have stabilisers mid mounted.  If you want to  
operate in waves then mount them toward the stern to reduce flop  
roll.  Use two not one.  They need to be long and slender with a  
volume at least 15 litres.

The 5/16" shaft with 16X16 prop will have very good feel - similar to  
riding a bike.  With the 1:2 box you will need around 1:3.5 in the  
chain.  This is a nice ratio as you can use mountain bike stuff.    
You can side mount the prop so it can be reached for cleaning.  The  
shaft strut will need to be stiff enough to prevent the prop from  
hitting the hull when you turn.

 From a practical use point of view, weight is really critical.  You  
should make an estimate of weight.  Count every nut and washer.  Make  
allowance for paint.  You should target 20kg or less.

As a matter of interest Mike Lampi launched his V15-6m last weekend:
http://hpb-er.blogspot.com/
He has some minor issues to sort but it went well for first time out.

I plan to give my V15-6m its first run this weekend.

Rick

> Date: Thu, 16 Jun 2011 07:46:06 -0700
> From: Dom Rumbolo <drumbolo at gmail.com>
> To: hpv-boats at hupi.org
> Subject: [hpv-boats] Flex Shaft Material Selection
> Message-ID: <BANLkTi=EAPZpGOmXKVALXQ+C1bwpmYKeVg at mail.gmail.com>
> Content-Type: text/plain; charset=windows-1252
>
> Hi Rick and the rest of the list,
>
>
>
> First of all I?d like to thank you for your huge contribution to human
> powered boating.  I?ve followed your threads around the Internet  
> and it?s
> been a great inspiration.
>
>
>
> I?m starting on my pedal-powered build, using a fiberglass surf ski  
> as the
> foundation.  I picked up a T-gearbox at 2:1, and plan to start with  
> the APC
> 16x16 prop, a 5/16? steel flex shaft, and chain gearing.  As has been
> mentioned, finding spring steel in the US is not easy.  Doing some  
> research
> on the Internet, this is what I?ve come up with and I?d appreciate  
> your
> input:
>
>
>
> A search for spring steel yields several grades of steel, including  
> 1095:
> http://www.tmtco.com/products/spring-steel.html
>
>
>
> Trying to find 1095 steel, I see that it is equivalent to W1 drill  
> rod:
> http://forums.dfoggknives.com/index.php?showtopic=6783
>
>
>
> Can?t find W1 drill rod in anything longer than 3?, but I see that  
> A2 drill
> rod is similar: http://www.onlinemetals.com/toolsteelguide.cfm
>
>
>
> A2 drill rod is available in 6? length and fairly cheap:
> http://www.mcmaster.com/#8888k416/ $26 shipped
>
>
>
> Alternatively, flexible sewer rod is available:
> http://www.flexmax.com/maxlife/cat1.html (MDA-72LC, powder coated) $41
> shipped
>
>
>
> I?m not sure of the material properties of the sewer rod, but it is  
> nice
> that it comes powder coated.  Here is some data on A2 drill rod:
> http://cartech.ides.com/datasheet.aspx?i=103&e=262&c=techart
>
>
>
> Thanks,
>
> Dominic
>
>
>