Whittle "Robin" Engine questions

[Boo]

Hi,

Quite a while ago before his sad demise, I asked for and gained Eric Whittle's permission to CAD up his "Robin" engine. In the usual way of things I did not get round to it but have now started this and have a few questions regarding the drawings that I found in SIC:

1. There does not seem to be a detailed drawing of the Cams for this engine, or am I missing something ?
2. Ditto the prop driver ?

Anyone know where drawings for these items can be found ? I have a full set of SIC back issues but all I can find pertaining to the cam is the attached which gives no dimensions at all ? The prop driver is easy enough to figure out without a drawing but I have no idea what the design process should be for a cam...

Thanks,

Boo

 

[RetNM]

I don't know if this will help. Normally cam designs are a set of tables which provide coordinates points around the cam periphery. Then draw lines by connecting the dots.

 

[Jasonb]

If you follow the description in issue 21 you will be able to plot the flank radius of teh cams and it also gives the base circle dia.

 

[Jasonb]

A single cam Should come out something like this based on his description

 

[petertha]

Do you have the SIC index? if not I can upload. Its advisable to check it because SIC was famous for 'errata' would sometimes come in subsequent to the main plans/build series. I did a 'Robin' search & pasted below. Some of it may be duplicative.

Years ago I started a Robin CAD drawing from SIC plans. I remember a few head scratchers interpreting the drawings but I cant remember if they were significant. Sometimes it helps to have the text beside you when drawing. Sometimes that doesn't help because I suspect certain engines were measured from actual engines & by different contributors vs design first, build second type approach. It is what it is. Anyway I can't recall specific Robin cam details, but if you do a forum search I wrote a post on glow engine timing using commercial engine (and some shop builds) which might be a good gut check. I think Whittle used very similar if not identical timing across many of his designs, probably because it worked. But don't hold me to that, this was more from my own observation. The thing to be aware of is the cam profile is one thing, but this gets transposed through the lifters & pushrods & rockers (any of which which may be at slightly different geometry) which will impact true valve open/close timing. Whether that is enough to fuss about is your call.

Omission, From Robin construction series 22-31
Robin, construction series P.E.L. Whittle (Eric): 19-23; 21-13 (2-3)
Robin, P.E.L. (Eric) Whittle, construction article 18-11
Robin, Whittle, 61-3, 62-32
Robin's augmentation, An omission in the Robin construction series P.E. (Eric) L. Whittle 24-31
Whittle, P.E.L (Eric) Robin construction series: 18-11; 19-12; 22-13 (1-3)

 

[petertha]

Hmm.. my memory is getting foggy. Were there not also Robin plans sold through one of the model engineering services? I might be thinking of something else though.

 

[Jasonb]

Just drawn out the cams, shaft and gear all from what is in Issues 19 & 21 and looks like Peter's

 

[petertha]

You can see the front & rear pushrods are at a slight fore-aft stagger relative to the rockers. If the cams happen to be centered, the timing (open/close) duration would be the same to both intake & exhaust assuming same cam profile. Otherwise they would be a bit different duration. Splitting hairs here practically speaking, but just pertaining to the point of 2D cam plate timing vs actual valve timing in 3D space. I think Whittle mentions in one of his other builds, possibly the V8, it didn't make a lot of difference on his glow engines. There are some nice YouTube videos of his engines running which are pleasant to watch & proof of the pudding.

Also FWIW I believe it was the Robin that had some funky glow plug mods to miniaturize it. Its a little bit of a watchmaker engine in some respects. Look forward to the build!

 

[Boo]

If you follow the description in issue 21 you will be able to plot the flank radius of teh cams and it also gives the base circle dia.

A single cam Should come out something like this based on his description

Just drawn out the cams, shaft and gear all from what is in Issues 19 & 21 and looks like Peter'sView attachment 143049

Yes, thanks very much for the replies, by following the info you provided and carefully reading the text (and ignoring the spurious .270 misprint in the original), I have managed to recreate what you have provided:

As an aside, can I ask what cad program you are using, Robin ? I like the way it shows the planes as bounding boxes in the output as you have shown... I am using FreeCAD which I am gradually getting more proficient at with time and practice.

 

[Jasonb]

That's Alibre, the planes will grow as the part gets bigger and can easily be toggled on/off if you don't want to see them.