Tips for making vacuum engine (flame licker)?

[Clonkex]

Hi all,

I recently found this video (https://www.youtube.com/watch?v=21xyKBRO_A8) about a V4 vacuum engine, and it got me thinking: maybe I could build a little single-cylinder vacuum engine from random stuff lying about the place. I have virtually no experience with model engines so far (other than maintaining the nitro engines on 1/8 scale buggies), but I'm fairly technically-minded so I thought it was worth a try.

I have some questions, though. How well does the piston need to fit inside the cylinder? That is, will a gap around the piston of about 1mm be a problem? How big (or rather, how heavy) does the flywheel need to be? Would a 1kg dumbbell be sufficient or too much? Is there any chance (in your opinion) of a vacuum engine running if the cylinder is not perfectly smooth inside? I mean, I've sandpapered it but it still has a tinge of rust inside (and does it horrify you that I'm hoping a rusty cylinder might work?).

It's late and I need to go to sleep, but I'll see if I can't get some pictures of my unsightly contraption up tomorrow

[Arbalest]

Welcome to the forum. Vacuum engines are very low powered so the fit and finish needs to be really good if you are to stand any chance of getting them running.

Have a look here, Jan's engines are very popular and he will email you plans if requested.

http://ridders.nu/Webpaginas/pagina_overzicht_happermodellen/happeroverzicht_frameset.htm

[b.lindsey]

Welcome from me as well. Please take the time to post a  brief introduction of yourself, your interest and anything you want to tell us about your shop, etc. in the introductions section.  That way more members will get to know you and provide more help as well. As to your questions here, a smooth bore and a very close fit of the piston are needed for vacuum engines. A 1mm gap would be HUGE!!!

Bill

[Clonkex]

Thanks for the replies

I know all about Jan Ridders' engines; I've been watching many YouTube videos of many different kinds of vacuum engines so I have as many ideas as possible for solving problems. The problem for me is that even I don't go for the unbelievably high-quality work-of-art styling of his engines, I still don't have the equipment to create custom cylinders or pistons. I.E., I don't have a mill or lathe.

Hmm... so a 1mm gap is going to be a problem.... when I say 1mm gap I mean if I push the piston to one side, the biggest gap is about 1mm. If it's in the centre, the gap is about 0.5mm on all sides. I lay in bed last night and considered ways of remedying this issue, and I believe I may have a solution, but it's a bit of a long-shot since you say these engines are very low power.

I still feel inclined to push on and attempt to make it work, even if everything I read says the bore needs to be silky smooth and everything else be very low-friction (however I think I can get all the mechanisms to be fairly low-friction if I rebuild the flywheel supporting frame). If you had to suggest one or the other, though, would you say I'm more likely to get a vacuum engine or a Stirling engine working with poor-quality parts? I much prefer the flame-lickers (I just love how they run), but a Stirling engine can be cool too.

Please take the time to post a  brief introduction of yourself, your interest and anything you want to tell us about your shop, etc. in the introductions section.

I've never been on a forum that specifically asks that you post in the introductions section before :O I'll go do that now

[Arbalest]

A stirling engine may be a better idea if you're limited on tooling. Have a look here and also try a search for "Easy build stirling Engine".

http://www.stirlingbuilder.com

[b.lindsey]

Clonkex,

Poor quality parts, poor fits, and friction are the enemies of both types of engines due to the low power produced.  Yes they are fascinating to watch and certainly do-able, but many here would suggest that you practice on something like an oscillating cylinder first to hone your machining skill and abilities to produce close fits. The gap you mention of even .5mm per side equates to .020" for those of us using the inch system and I can only repeat...that is a HUGE gap and would make either type of engine a non-runner. Piston/cylinder fits in atmospheric and stirling engines need to be in the order of .001" per side or less.  I wish you well in your model making and I think everyone here is more than willing to help and offer advice. I certainly don't wish to be a wet blanket in this regard, but quality and good fits are just mandatory in these engines and I don't want you to become frustrated by investing time and effort when the outcome is doubtful.

Bill

[tvoght]

Hi Clonkex,

I'm with Arbalest. You can make a "tin can Stirling". Search for that phrase and you'll find lots of stuff.

Because a "tin can Stirling" uses a diaphragm (like a piece of balloon) instead of a piston, that critical fit is eliminated.

With your tooling set, You'll have a much, much better chance of first-time success.

Your attitude is good about accepting failure, but you'd be so much happier and motivated if your first build ran.

Regards,
--Tim

[Ian S C]

Hi, I'm back, the piston should just slide down the bore under it's own weight, and when you block the end when the piston should virtually stop.
     A hint;  if you can find an old car shock absorber, open it up(carefully), inside you'll find a tube a bit over 25/30 mm dia., this has a lovely smooth bore, it's easier to make pistons than cylinders.  There are sites on the web about making pistons from epoxy resin, I'v never tried it, I make mine from cast iron, but I'm not beyond using shockies for cylinders.
     As I mentioned in your other thread, a tin can Stirling/ hot air engine would maybe a better starter type of motor.
                                            Ian S C

[mklotz]

Some ideas to fuel your imagination...

All glass hypodermic syringes make reasonable piston/cylinders if well lubricated.  The type with a rubber or plastic piston don't work as well - too much stiction.  You may be able to find the all glass type at a veterinary supply.

Hobby suppliers sell telescoping brass tubing that could be made into (an admittedly small) piston/cylinder pair.

As a machine poor kid, when I built my perfusion machine, I used an automatic door closer as a ready-made air pump to power the blood circulator.

I'm not an auto mechanic but could a disc brake actuator be adapted somehow? 

[Roger B]

I'm not an auto mechanic but could a disc brake actuator be adapted somehow?

The first engine I built used the cylinder and piston from a drum brake (~1" 25mm). This was an oscillating cylinder steam/compressed air engine made using an electric drill in a stand. It would run from a foot pump with significant effort and was also once connected to a bike dynamo and my mother's pressure cooker. With around 2kW heating the pressure cooker it managed to light a small (1W?) torch bulb 

[Ian S C]

At one stage people in USA could get free samples from Airpot Corporation, they have a very wide range of glass cylinders with fitted graphite pistons.
www.airpot.com/precision-dashpots.html
I imagine there are other companies out there.
                                            Ian S C

[Clonkex]

Thanks for the replies, guys, and I apologise for the late reply. Rest assured I have read every post, and there's some really good ideas there, but I've suddenly become really busy over the past few days and I don't have the time to reply individually or even work on my project. I'll come back as soon as I finish my current work; I hate not finishing a project!

Cheers

[b.lindsey]

Projects are seldom finished in a week or two Clonkex so no worries. We will be here when things let up with the work load.

Bill