Struggling to fit in?

[RussB]

I feel a bit like the odd one out :hDe: a bit nervous to reveal my true ambition! Ultimately, I don't know which club or forum is for me, but I prefer it here although it feels like the title just doesn't fit the bill for me

Sooo, my true feelings right now to explain that, is the model engine in my dream project is really probably the least important bit - I will enjoy it, but I have no preference - anything will do, and when I say anything, I think I mean IC - I don't dislike steam and love to see them being loved but it doesn't push my buttons at all from a personal project perspective.

I'd like to link my undecided engine to a hydraulic pump via an appropriate gearbox and drive at least 2 variable displacement axial piston motors (hopefully reversible via the swash plate with an RC servo)- all built from scratch - and I'd like to plant this in a tracked vehicle and I might as well build that too but the chassis/bodywork will probably be just designed by me, and laser cut by someone else.... but like the engine, I've no preference. I'm British, so I'm thinking something British and modern, Challenger II fits the bill, but anything will do.

I'm new to this model engineering lark and look forward to getting stuck in. I don't expect to able to achieve my ambitions in the next month or 2, and to be honest progress in the next year or 2 would be nice. I'll just concentrate on some simple IC engines to get me going.

Getting back to knowing where I fit in, I've looked about on the net and google's taken me to various RC model forums for earth movers and JCB's and stuff which fascinated and inspired me more but the good chaps there just seemed to be buying off the shelf plastic parts/pumps and so on and running them on batteries etc. with sound effects - it's not really ticking my boxes, would anyone be able to recommend a forum or club online where people either just get up to their eye balls in anything mechanical or anything hydraulic perhaps - seems a bit far fetched!

 

[Brian Rupnow]

Russ--We all have to begin somewhere. If you are a true "Newbee" to model engineering, then you will want to tackle some simple projects first, and you will want success with these projects. Nothing puts one off a hobby faster than getting into a project which is too advanced for them right at the beginning, which leads to frustration and ultimately failure. My advice to you is as follows.---Even if you don't find "steam" or "compressed air" engines very exciting, they are the simplest of all engines to build and have immediate success with. I recommend that you build one or two "oscillaters" or as they are called "wobblers". If you have success with these, then tackle a single cylinder mill type stationary engine, and perhaps a beam engine. Research "Elmer Verbourg"--He designed many wonderful small engines and the plans are free on the John-Tom website.You need to build 4 or 5 of these engines before tackling even the simplest internal combustion engine. For a first internal combustion engine, the Webster seems to be everybody's favourite, the plans are free on the Internet, and it does not require a lot of exotic materials to build. Once you have built your first successful internal combustion engine, then you can start to move in the (very ambitious) direction you have outlined in your post.---Brian Rupnow

 

[Swifty]

Hi Russ, we all have to learn to walk before we can run, I like your enthusiasm. A friend of mine built a remote controlled track vehicle powered by a brush cutter engine. Here's a link to it. [ame]http://m.youtube.com/watch?v=jgY7nr2lKfo[/ame]

Paul.

 

[abby]

If you can't find the forum you would like then start your own , it is very easy and everyone was started by an individual who could not find exactly what he wanted .
The drawback is that forums need content and this is not so easy.
Most forums have hundreds of readers but very few contributors , and good contributors are thin on the ground.
Many projects are started with the best intentions and are meticulously recorded but a lot can happen and the progress posts gradually dwindle and stop.
You might find what you are looking for on a builders web site /blog rather than a forum , there are thousands of tracked vehicle enthusiasts so there must be some build logs somewhere.
Dan.

 

[RussB]

I will certainly be walking before I can run, and when I've finished walking and got some sort of IC engine going (I'm leaning towards a simple 2 stroke compression ignition) I'll probably go the jugular and try a pneumatic axial piston pump with a view to maybe converting/recycling it to hydraulic

Nice model Paul, looks nifty!

I've stumbled across a few interesting reads which I'll digest over the coming months/year,

Theory of Axial Piston Pumps:
http://www.deltaq.com/pistonpumps/theory 2008.pdf

http://hydraulicspneumatics.com/other-technologies/chapter-8-air-and-hydraulic-pumps-part-2

http://www.insanehydraulics.com

 

[MachineTom]

In today's society everyone is so use to having what then want NOW. That most begin to assume that making a model engine is the same thing, just buy some stuff, buy some plans,buy some books, buy some tools, and a month later they are done with whatever they wanted to make.

That never will happen, unless you are already a machinist. So first you need to learn the tools, lathe, mill, cutting, threading, boring,drilling, planning, making jigs, fixtures, tools, assembly. All the time making stuff that is not related to your project you have described.

At some point you might begin making parts for that project, but in all likelihood something else will catch you eye and you will go that direction.

Its not the destination, as much as its the ride that counts.

 

[DICKEYBIRD]

So first you need to learn the tools, lathe, mill, cutting, threading, boring,drilling, planning, making jigs, fixtures, tools, assembly. All the time making stuff that is not related to your project you have described.

At some point you might begin making parts for that project, but in all likelihood something else will catch you eye and you will go that direction.

Its not the destination, as much as its the ride that counts.

Sage advice, that!

 

[RussB]

MachineTom,

I have a lot of experience with mechanics growing up (ie cars, motorbikes, engines, gearboxes and valves), which led be down a careerer path giving me a lot of experience with mechanical design, and now as I hobby I'm progressing to actual metalworking (rather than doing everything on a computer in 3D and never/rarely actually seeing the final product). I'm young enough to not know what I'm doing, but old enough to realise that, but you're right, I do want it now but I know the best I can do "now" is start learning.

As a brief introduction I've been reading "Metalwork" by R. Sandham and F. R. Willmore which was given to me last year as a start point by a model engineer. He also gave me Engineering Workshop Practice (3 volume set revision 2) by Arthur W. Judge which is far more detailed if I want to focus on a particular subject. I've been reading these with enjoyment.

In the words of Arthur W. Judge
"... it is realised that the scope of the subjects coming within the field of workshop engineering practices is a very wide one-a fact that makes it impossible to deal exclusively with each and every branch of that subject..."

I think you've highlighed/reassured me which subjects I need to be looking at so thanks, although I hope your not suggesting that my ambition of "progress" in the next 1-2 years is optimistic - I don't expect to get it right first time, I hope to learn while trying - preferably without hurting myself

 

[RussB]

ohh.... I'm also keeping an eye out at Harrogate show this weekend for this book which looks really good "http://www.chesterhobbystore.com/lathework-a-complete-3908-p.asp"

 

[jack.39]

A good thing! Most hydraulic pumps in general use are of the simple, constant volume design, meaning each revolution of the input shaft produces a fixed volume of fluid flow, such fluids being for practical purposes, incompressible liquid. This means that since the pump must be sized to meet at least the volume needed to get the job done, it's "overflow" must be dumped, this representing wasted energy and efficiency.

Variable volume pumps can be used to provide just the flow needed, no more, and still meet varying flow requirements. I believe this is the concept used in the "variable swash plate" construction. One application I recall used in mass produced numbers, was the Air Conditioning compressor in General Motors' ill-fated Fiero motorcars. Obviously, such pumps are expensive, as well as more complex.

Today's fuel-injected vehicles no longer use constant-volume fuel pumps, but rather than resort to varying pump output volume through mechanical means, the pump's speed is varied constantly, in order to maintain constant pressure at the fuel injectors. Such control is obtained electronically. When I first heard of this scheme, perhaps 15 years ago, my reaction was, "This is madness"! I expected pump life to suffer. However, the opposite proved to be true. The pumps are now "worked" far less laboriously than before, and the pieces of this puzzle DO fit together reasonably well. jack

 

[RussB]

Jack, I'm hoping with the variable volume pump/motor I'll be able to have positive and negative angle on the swash plate giving me forward/netural/reverse for each track servo controlled. That's why I've focused a bit on the concept, plus obviously with a hydraulic power source I could run all sorts of extras!

EDIT* I'm not 100% sure this will work as I hoped, with the swash plate at 90° to the piston axis it would be in neutral, and moving just off vertical would give high rpm low torque, and moving further away from vertical would increase the stoke, lower the RPM and increase torque so the gear ratio would go from low, to high, to neutral, to high reverse, low reverse - I could be talking tripe, I don't even know if it will reverse I'm just a nutter lol! ;D I think the best bet is to keep thinking it through and maybe try to get my hands on one - I've got an old lawn mower with a hydrostatic variable speed transmission, might have to rip that to bits and have a look whats inside

 

[MachineTom]

There is a pump/motor very compact made by Eaton Corp. They are radial rather than an axial set up. Variable volume pump, fixed displacement motor, its constant torque, variable HP design. the rotors are mounted to a central carrier, both rotors use BB as the piston, smaller on the pump than the motor, to give torque multiplication, on the pump side the swash plate is an outer race to match the balls, and is pivoted left and right, which varies the ball to race distance, therefore the stroke of the balls giving a pumping effect to the rotor. The oil flows through the central carrier and into the motor section, the outer race is fixed in its offset to the rotor, this provides the displacement to drive the rotor and turn the output shaft to which it is affixed.

A 5hp pump/motor is about 8" diameter, and 6" wide. Eaton Hydrostatic is what to Look up.I've worked on the Model 6 versions, the manual shows great illustrations of the blow up.

 

[jack.39]

Jack, I'm hoping with the variable volume pump/motor I'll be able to have positive and negative angle on the swash plate giving me forward/netural/reverse for each track servo controlled. That's why I've focused a bit on the concept, plus obviously with a hydraulic power source I could run all sorts of extras!

Your interest is to be commended! FWIW, 'way back when, talking maybe mid 1950s to 1960s, as A/C came into common use in vehicular building, most makers opted for plain old piston pumps, which were actually nothing more than basic air compressors now squeezing Freon gas. General Motors began using their Frigidaire axials, which were long and slender, cylindrical in shape, had only the skinny pistons reciprocating inside, rather than pistons and connecting rods, these pumps were extremely quite in comparison, vibration-free, and fairly long-lived. And, they were expensive. It always seemed likely to me that G.M. was able to justify their use based on Frigidaire being a G.M. Division.

But, I always drove Ford products! I dreamed of converting one of my cars to use of the G.M. A-6, but never got around to it! Here's a bit of info, and a very poor blow-up diagram:

Car air conditioning has been around since the 1940 Packard. One of the most recognized manufacturers, Frigidaire, has been manufacturing air conditioning components for automobiles since the early fifties. Their first successful complete air conditioning systems were installed in 1953 Cadillac, Oldsmobile and Buick cars. One of their more popular successes was the design of the model A-6 compressor, which was used by General Motors for more than 25 years. The A-6 was Frigidaire's first axial designed compressor. This compressor used a cast-iron cylinder and heads with a steel case and "swash" plate. The A-6 designation related to its axial design and the fact that it was a 6-cylinder compressor unit. The interior of the compressor also had an oil pickup and sump system to lubricate the internal parts. The A-6 compressor will push out 27,000 BTUs at 2,000 rpm and as high as 42,000 BTUs at 4,000 rpm with a discharge rate of 240 p.s.i. That's enough cold air to cool a small house (most home window-mounted air conditioners are only rated from 5,000 to 12,000 BTUs). The compressor functions much in the same way an engine does but without the ignition and combustion strokes. An A-6 is rated at 1.5-inch bore with a 1.2-inch stroke and 207cc displacement. That's about 121/2 cubic inches. The A-6 is also highly adaptable. It can run in 6, 12 or 24-volt systems if you install the proper clutch coil. They are a pretty resilient unit too; they can turn consistently at 6,500 rpm all day without overheating, and you can turn them in either direction and they will function in the same way. Originally designed to be used with R-12 Freon, modern adapter kits allow the A-6 to run on the newer, more environmentally friendly R-134a.
By 1969, 54 percent of all new American production line cars were equipped with air conditioning. In addition to offering A/C as a factory option, most dealerships were installing aftermarket air conditioning at their own facilities using the A-6 compressor as the major component. By 1997, 96 percent of all new cars were factory-equipped with A/C.
Frigidaire compressors used in the above General Motors and import applications were activated by a high pressure or superheat switch located in the back of the compressor. Although these units look the same, there are slight differences in the size of the hole and its position on the back of the compressor for the switch. Also, compressors used in import applications or GM cars built after 1980 had metric-threaded mounts. Ford units did not use a switch on the compressor. Many different clutch and coil assemblies were mounted to the front of these compressors to make them compatible with the engine application for which they were being used. Single and double v-belt pulleys as well as several poly-groove serpentine belt applications attach to the A-6. The hoses for the GM air conditioning system were both attached to the back of the compressor by way of just one fitting. However, because of the versatility of the A-6, many back plates are available to adapt this compressor to numerous other configurations. Plates can be found for York and Tecumseh roto-lock fittings as well as the tube o-ring style fittings. Some 4WD enthusiasts have even built onboard air compressors for their off-road trucks using the A-6 as the primary source of pressure. jack