Johansson´s Pocketbike

[Johansson]

I am sorry about your eye, I hope it will be well soon. I almost did the same thing today when I was grinding on one of the mounting plates, even though I wore good protective glasses a small piece of metal jumped into my eye. I could wash it away easily but one starts to think of what could have happened...

Ohh, it is sooooo much left to do before it is ready to be started. As soon as the engine is mounted in the frame it will be much more fun to work on it though because everything I will do after then will make the bike more ready-looking, everything I have done so far has just added things to the pile of metal on my desk and that ain´t exactly thrilling in the same way. ;-)

//Anders

[skyfrog]

Hi,

Would you guys mind if I cut in this topic.

Be careful of the lathe, it is very useful in making jet engines, but I think it is even more dangerous than the grinder.

Last week I read of a news here about a lady worker cleaning inside a CNC lathe for removing the scraped chips, God only knows why the power didn't shutdown before cleaning, and the spindle is still rotating in high speed, so her hair got stuck and was pulled in by the chuck. You can imagine how horrible the situation was, after that no one dare to walk into the machine shop for next few days.

[Anders Troberg]

Ohh, it is sooooo much left to do before it is ready to be started. As soon as the engine is mounted in the frame it will be much more fun to work on it though because everything I will do after then will make the bike more ready-looking, everything I have done so far has just added things to the pile of metal on my desk and that ain´t exactly thrilling in the same way. ;-)

I know the feeling, I see it a lot as a programmer. The best part is when you've done a good job, so that everything just falls in place so fast it leaves you thinking "What, is it ready? So quick?". On the other hand, if you have made a bad job, then this is where the hell begins...

[Fricke]

Johansson -

Those little comets are quite painful to get in the eyes... I normally wear contactlenses, they have saved me many times... Even with proper protection there is allways some that find their way to the eye... One of lifes big mysteries I guess...

Well it´s now the fun begins =) when most of the "boring" work is done. And the "thing" gets to "life".

I´m going to source the special 14 mm bearings for my freepower shaft this week. And try to find some suitable gears, I´m looking for a 5:1 gear ratio.

//F

[Johansson]

I did some calculations yesterday on the flame tube, and came up with a rough guideline with a total hole area of 100mm2 less than the compressor inducer area. I will spend around 200mm2 on cooling holes but since they will have a small diameter the throughput will probably be minor.

The vapour tubes will be made from four 12mm SS thin-walled tubes, according to John (racketmotorman) the effective area will be reduced by the bends to half of 113.1mm2 so I have estimated the total flow area of the vapour tubes to 250mm2.

When I made the inlet bend on the combustor it was not possible to fit is as low as I wanted, so the dillusion holes will have to be situated on the upper part where the air enters the combustor. If the flame is pushed towards the opposite flame tube wall when I test it I will have to fit some kind of flow guidance plate, but until then I won´t bother.

The clearance to the casing is set to 15mm, I believe that 10mm could be enough but it is better to be on the safe side...

When I have come up with a final design I will post a drawing here for comments.

//Anders

[Johansson]

Finally! An unexpected vacation gives me much more time to spend on the bike from now on, hopefully I will have most of the vital parts done a few weeks from now.

This week I have ordered the SS tubes for the vapour system, the fuel nozzles and a nice lid for the fuel tank. A lucky find in the Swedish gold mine "Claes Ohlson" gave me the stainless cap for the flame tube, very helpful since I now won´t have to make a bowl-shaped cap from sheet metal.

I have decided to have as few gauges as possible visible when driving, a pressure gauge for P2, a TOT gauge and a bicycle computer measuring speed is all that I need to monitor. I will add measuring points on the engine for measuring compressor outlet temp, fuel pressures, turbine outlet pressure and perhaps bleed air temp, but these gauges will only be needed when I am testing the bike so they will be disconnected when the engine has proven to run reliably.

//Anders

[Johansson]

A quick pic of the stripped frame before I start fitting the engine...

//Anders

[Johansson]

This is what the flame tube roughly will look like, there will be four vapour tubes but I only drew two to make the picture easier to understand. The vapour tubes is drawn in perspective in the picture if you think they look strange, they will be normal J-shaped ones. I will have a stainless spring around the middle nozzle holder to put some pressure on the flame tube and keep it from jumping around.

I hope that the length of the flame tube is enough for good combustion, but I guess that I will find that out pretty quick when I start testing it... ;-)

//Anders

[Johansson]

John:

I´ve been thinking about the free power turbine. The space available for the housing is quite limited for obvious reasons, and the gearing assembly will also require some space in the frame. Since the housing will have nozzle guide vanes in it directing the exhaust jet towards the free power turbine, is a big snail housing really needed?

Could I just make a "large enough" snail narrowing down as it goes around the NGV that is opened to the NGV the entire way around?

If I would only loose a few % in efficiency it would be the best way to do it since I will try to keep everything inside the frame without anything pointing out, both for the looks and to avoid burning pants while riding it... ;-)

The gearbox seems to be a very complicated part, so I have thought about gearing the turbine down with a belt drive. It would save me much work since I won´t have to mill a gearbox and integrate it with the turbine shaft.

//Anders

[Zippiot]

that is gonna be oone hell of a gear ratio!

depending on the ratio you are looking for i might be able to help you, i designed a few gearboxes for robots for the highschool robotics team. we geared a 20k rpm motor down to about 1k, it had enough torque to move a 120 pound robot with tank treads [halftrack really]. and the motor was less than 3/4 of an inch wide and less than 2 inches long.


gearboxes dont always have to be boxes! you can attatch the gear to some stock [keystock], and pretty much channel that anywhere you want, as long as it is in a straight line.

we used this to get a motor and gearbox at opposite ends of the bot to keep it ballanced. you may ask how this helps you? simple and complicated depending...

if you gear it down enough first, you can actually run the keystock through you existing frame!! we did it with an aluminum box frame and it worked great. so, if you are having a hard time placing the gearbox, put parts of it inside the bikes frame.

[racketmotorman]

Hi Anders
It would be possible to have the "scroll" off to the side , rather than radially around the turbine , sorta like I did with the bikes freepower setup
http://www.ivcity.com/john/index.html
rather than the karts
http://www.nickhaddock.co.uk/johnkart.htm
I had exactly the same limited space problems as you with the bike, hence the "novel" scroll on the axial turbine , but the same could be installed on a radial inflow turbine to turn it into a sot of hybrid axial/radial inflow turbine .
The kart had plenty of room and the placement of the gas producers outlet suited a "normal" radial inflow scroll that had rudimentry guide vanes in it simply to hold the side in the right place .
Unfortunately the lower gas densities and gas velocities within the freepower mean we have to contend with large sized ducting etc .
I'd be a bit wary of using a belt drive , lotsa radiant heat around it as well as conducted heat along the turbine shafting , the rpm could be too high for a belt thats able to handle the torque , also any frame flexing will put the belt under extreme loadings . A broken belt would unload the freepower turbine which could cause a few overspeed problems :-((
I'd imagine your potential freepower rpm will be rather high and a gearset is almost a necessity .
Having said all that , it might still work with a belt , if you're careful and do the design work correctly .
My timing belt design manual only gives horsepowers ratings of around 1hp at 10,000 rpm with the lightest/fastest belt :-((
Have you looked at the ~5:1 gearboxes off large metal cutoff saws , I pulled a burntout saw apart and turned off the electrical windings on the pinion shaft and it might work for a smallish freepower .
Making a DIY turbine bike isn't an easy task , theres never enough room for everything , including the rider :-))
Cheers
John

[Johansson]

The gear ratio will be around 3:1 so the free power turbine will be turning at a max rev at a bit over 30.000 rpm. The bike will be geared for a top speed of 100 km/h, I guess that I won´t have the courage to go any faster... ;-)

I think that a belt drive will be best for this because it can work in the open without lubrication, a gear box would have to be tightly sealed to stop dust and sand from getting inside and alignment of the gearshafts is much more important than on a belt drive. Since a belt is not enclosed it will be much easier to change gear ratio if I want to increase the power turbine rpm and get more power.

//Anders

[Johansson]

Hi John!

I will have to check with a company that sells belts to find out if it can be used, the belt can be shielded from radiant heat and it should be kept quite cool by the outside air even if the belt sprocket is heated by the shaft.

Frame flexing is not an issue since the two sprockets will be fitted close to each other, the idea is to gear the turbine shaft down by the belt on to a second shaft, on the opposite side of that shaft will the chain sprocket be mounted. The chain drive on the bike is on the left side. When I have time I will make a mock-up on the bike and post a picture for easier understanding...

//Anders

[racketmotorman]

Hi Anders
The tooth belts need to have their shafting in good alignment otherwise it loads one edge of the belt and they fail from that tight side.
30,000 rpm might cause problems with centrifigal loading on the belting.
Also, there is often a minimum centre distance between shafting to provide sufficient teeth in engagement on the smaller gear , when using larger ratios.
Have you considered using a steel turbine pinnion gear and a selflubricating plastic gear for the larger one .
Normal karting sprockets and chain (racing grade) can handle 20,000rpm .
Cheers
John

[Zippiot]

one last suggestion, make it pro. tanks use hydraulics, i made a hydraulic drive once. the gear ratios are easy to swap out b/c all you do is unscrew a fitting and screw in another. it takes up NO room, as all it is is pipes and tubes running down (or inside) the frame. all you need is to attatch the pump to the turbine, plumb it resivoir and all, and attatch the drive turbine (kinda like a reverse pump, but instead of the shaft spinning the fluid turbine the fluids move the shaft). also, the clutch is as simple as it gets; the clutch is a manual bipass valve, it is throttleable and cheap as hell. plus no expensive clutches plates and such!

it really isnt complicated at all, and there is no need to do prescision work on the alignment.

i think some new honda atv's use hydraulic drive