jamiep
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Post by jamiep on Oct 26, 2013 19:55:11 GMT -5
ok... so say i go the ST/VT 50 route for the freepower turbine... long ago, we talked a little about putting a clutch on the output of that before the cart axle to keep the turbine in the higher rpms... current thoughts on that? your little kart seemed to scoot.
jamie
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Post by racket on Oct 26, 2013 20:58:17 GMT -5
Hi Jamie A clutch would improve that initial acceleration lag inherent in all fixed freepower systems when the lack of rpm means the available high stall torque still isn't producing a horsepower , a good "high horsepower" karting clutch would be the way to go , .............due to the fact that the freepower , even when the gas producer is idling , will be spinning quite fast , possibly to the point where the centrif. clutch is starting to activate , it might help if there was some sort of disc brake on the turbine shaft to lock it prior to you wanting to get under way, and/or some sort of wastegate where the gases can be vented before reaching the freepower stage during idling conditions . This Site might give you some help www.noramclutch.com/www.noramclutch.com/go-kart-clutch/We probably need a clutch that activates at between 25-35% of the freepower max rpm , so for a karting chain/sprocket setup where max rpm of the freepower will be 20,000 rpm the lockup will be in the 5-7,000 rpm region . ...............so we'd be looking at top end karting gear for both chain and clutch . My 2 shaft kart went reasonably well for a simple setup , it was a bit sluggish off the mark but once up to ~ 30mph-50kph there was a real push in the back acceleration from then on ..................if only I'd had a bit smoother length of tarmac, instead of that rough service road to the dam, to wind it out on :-( Cheers John |
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jamiep
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Post by jamiep on Oct 27, 2013 11:05:22 GMT -5
Your kart had resonable takeoff but you said it was still accelerating hard at 70mph... i might do it the way you did and just gear a lower on the shaft...50-70mph top end would be plenty for me... seems with lower gearing it would get there quicker as well.
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Post by racket on Oct 27, 2013 15:49:20 GMT -5
Hi Jamie
Yep , still accelerating hard when I had to back off due to the "undulating" road surface , the kart was becoming uncontrollable .
The kart was geared for a tad over 60mph at 15,000 rpm of the freepower , and could have achieved 90mph at the 22,000 rpm limit of the racing chain being used .
Originally I purchased a 10 tooth sprocket for the freepower and a 86 tooth for the axle but had to go back to an 81 tooth as the chain was rubbing the chassis rail with the 86T.
The kart was able to accelerate to ~60mph in ~100 metres ...........with some sort of clutch arrangement that would have been a lot quicker as it took ~5.1 seconds to cover the first 50 metres but only 2.4 seconds for the second 50 metres, its always that first bit that takes so long with a fixed connection between freepower and axle .
Cheers
John
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jamiep
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Post by jamiep on Oct 28, 2013 10:25:46 GMT -5
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Post by racket on Oct 28, 2013 16:13:25 GMT -5
Hi Jamie
Yep , something to keep you busy for a few months :-)
Cheers
John
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jamiep
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Post by jamiep on Oct 28, 2013 20:28:51 GMT -5
does anyone have any recommendations on a brand of clutch? Or ones to stay away from? I am looking for something that will hold up to the freepower rpm around 20,000. Probably going with 3/4" shaft per Racket. I have seen some kart clutches that have swappable springs to change lockup rpm...some as high as 5,000 rpms. Seems like a good way to let the freepower "idle" spinning.
jamie
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jamiep
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Posts: 102
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Post by jamiep on Oct 28, 2013 20:29:58 GMT -5
..ps...Basically, i don't want to build this kart then strap a bomb (crappy clutch) on it.
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Post by racket on Oct 28, 2013 22:01:07 GMT -5
Hi Jamie
I'd be Googleing around to find a clutch capable of handling 30 hp at 15,000 rpm , this it getting up at the top end of racing kart outputs for centrif clutches and direct drive power plants .
Cheers
John
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jdw
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Posts: 41
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Post by jdw on Oct 28, 2013 22:20:15 GMT -5
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jamiep
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Post by jamiep on Oct 29, 2013 10:10:27 GMT -5
Did some research...haven't found any clutches that even mention numbers over 10,000...and certainly not horsepower in the double digits... I may decide to do a 2 stage chain reduction at like 15:1 which would put the kart around 50mph and probably some good acceleration.
jamie
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ozbooster
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Joined: October 2013
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Post by ozbooster on Oct 29, 2013 15:46:19 GMT -5
As a newby to this stuff and only have the little i have learnt from my turbine so far to go by, but do you need a clutch, when the freeair turbine is essentially a torque converter a good brake on the drive shaft and capability of locking it as a park brake (start and idle) not good enough  |
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Post by racket on Oct 29, 2013 20:49:39 GMT -5
Technically we don't need a clutch , but even with a gas producer on full power and a stalled freepower at nil rpm with the brakes on we have lotsa torque but no horsepower and its horsepower that accelerates a vehicle , the horsepower soon starts to be generated once the freepower starts to spin , but theres a lag period of a few seconds when things are a bit slow until the freepower blade speed starts to rise and the "distance in time" component of horsepower is happening . My 2 shaft kart developed 160 lbs of "drawbar" pull with the gas producer at full power and the freepower stalled . My first turbine bike should have been developing ~600 lbs of "thrust" between tire and road at stall but still had only modest initial acceleration www.youtube.com/watch?v=P-5PgWqgIJoBy incorporating a centrif. clutch in the system the freepower can get up to ~25% of its rpm and be producing roughly 50% of its max horsepower for vastly improved acceleration times . Hope this helps explain it :-) Cheers John |
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ozbooster
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Post by ozbooster on Oct 30, 2013 16:06:29 GMT -5
Sure does , thanks John  |
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jamiep
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Post by jamiep on Oct 30, 2013 19:13:09 GMT -5
The VT50 turbocharger arrived today...heavy beast. This will be used for the freepower section. A couple of questions- trying to get it apart now..seems stuck. any tricks to separating them?
I believe the current plan is to use chain or timing belt from freepower to a reduction. on the reduction jackshaft, I will have a clutch on the other side of it...this will allow the clutch to run in a reasonable rpm. probably run 40 size chain from clutch to axle.
My gas producer will run at 100% all the time and i will use a butterfly type valve to bypass all the thrust while the kart is at idle...when I want to roll, the gas pedal will close the butterfly to add or decrease the power to the freepower. With the 2 stage reduction, i should be able to keep the freepower idling at 5,000 or so rpms.
jamie
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