Landspeed bike with DIY gas turbine

[Johansson]

Today I got the spare compressor wheel and bearing kit I ordered before christmas, I hope I won´t need them but in case I do I don´t want to wait two or three months for the parts.



Always interesting to compare this massive compressor wheel with household items, here is it next to a 50cl beer can.

[ernie wrenn]

Planning ahead is just WRONG!! It will never break if you have spares.

Ernie

[Johansson]

Since our race team has a history of wrecked bearings and melted turbine wheels dripping out of jet nozzles I feel that it isn´t the worst of ideas to get some spare parts just in case... ;D

Did you get my PM?

[Johansson]

I got some more work done on the starter today, another days work and it will be ready for testing.

[Richard OConnell]

Very nice!! I was looking at your motor that you're using as the starter and i was wondering what kind of peak HP it makes.

[Johansson]

Thanks!

I am not really sure, a friend bought it on Ebay without all specs but as it comes with a 120A controller it has to be quite powerful. Racket had success with a modified automobile starter so if this turns out to be a failure I will have to pay the local scrapyard a visit.

[turborico]

Those brushless motors can be pretty impressive. I used to fly RC planes and helicopters, and since brushless motors and Lipo batteries have matured, there hasn't been many reasons to stick with nitro engines.

Do you have the model number from the motor?

Do you have plans to control the motor's ESC? If you were already using a microprocessor ECU for the engine, it'd be pretty straightforward to control it from that. I know the Arduino has a servo library that could be helpful.

[Johansson]

My plan is to eventually use the Arduino to make a startup sequence, but until everything is sorted out I will use a servo tester to rev the brushless starter. I will try to find out some more info about the motor.

I made some better guides for the starter plate today, these ones are 30mm long with a snug fit to the guide shafts so now there is virtually no play sideways for the starter.



I also made a hole for the cables so they won´t end up jamming the compressor wheel. One thing I found when testing the rig was that the alignment between the motor and the turbine shaft is off 1-1.5mm so I will have to modify the motor mount so I can move it a bit sideways.

Cheers!

[Johansson]

Yesterday I modified the starter mount so it could be centered over the compressor nut and cleaned the engine internals from grinding dust and other small pieces of dirt.



A quick test with the starter showed promising results, I had to lower the oil pressure a bit to keep the starter from stalling but then it managed to get the shaft up to revs very fast.



Next week I will fit an oil pressure gauge and a bleed valve to better control the oil pressure and do some serious testing of the starter to find out what revs it can bring the shaft up to.

[Johansson]

Minor setback today, I tested the starter with 1.5bar oil pressure and 20°C oil temp and the starter couldn´t rev the rotor higher than 5500rpm.

That is only 50% of the revs needed to start the engine so it wouldn´t help lowering the oil pressure further or heating the oil. My plan is to finish the engine first and then tackle the starter problem.

As you all know John had problems starting his engine as well, so I was not really surprised when I found this out.

[racket]

Hi Anders

Bugger :-(

I found that self sustain is ~22,000 rpm , anything less and it resulted in a hung start .

How did the motor feel after the test, any overheating , what voltage were you using , have you checked its no load rpm vs voltage to get its Kv rating ??

I was looking at these....... www.unitedhobbies.com/UNITEDHOBBIES/store/uh_viewItem.asp?idProduct=5139 ,unfortunately, it would need a 3:1 stepup gearbox to get the required rpm , but decided we may as well use the auto starter as they'll both weigh about the same and be roughly the same physical dimensions but the auto starter can be had for a fraction of the cost :-)

Cheers
John

[Johansson]

The cables heated up quite fast so any full power runs longer than 10-15sec would probably overheat something.

The motor was running at close to 25V.

I think I´ll try an air starter next time, my father has a scuba compressor that honks out 200bar and an air grinder fed by that kind of pressure would kick some serious ass I think. (we´re discussing this via mail right now John and I, but I thought I should tell you guys in what direction the discussion goes)

[racket]

Hi Anders

Mmm, hot cables sorta means she was sucking her juice , 5500rpm on 25 V =220 Kv , "normal" sorta largish outrunner specs .

Yep , looks about right :-)

Cheers
John

[Johansson]

Oh well, I am used to all kinds of setbacks while developing jet engines so this is no big deal at all.

I spent over a year struggling with a mysterious vibration at 35.000rpm in my pocketbike turbine without loosing faith so I am absolutely certain that I will get this bike running, no matter how long it will take.

[racket]

Hi Anders

Perseverance pays off :-) ......... even if it gets a bit disheartening at times when the failures keep repeating themselves and there doesn't seem to be an end to them :-(

Turbo rotor dynamics are very complicated , have a read of this...... rodyn-inc.com/ISCORMA3_Gunter%26Chen_TurbochargerVer2.pdf ....................LOL, might help explain the difficulties we experience when changing over from brass bushes to ball bearings, and why its probably better not to ;-)

Cheers
John