Fastest Speed by Scooter 70

[Folkert@MinaRally]

If they put an overall equal energy, but the longer geared bike will take more time to accelerate, then we are not taking about the same power. The robots have not equal power.
This is like the space probes I described before. The ionic engines have very low power. So it takes years to get a high speed. With an huge chemical rocket engine you could get to the same speed in less time, so you have to consume the same ammount of energy in less time = higher power. But the ammount of energy consumed is the same, let alone the engines efficiency.

Okay okay, let me disect that part. I DO understand what you are saying here.
Now are you also saying that both these rockets have the same acceleration?

Let me give you a real life exampple and then maybe you can explain.

Forget the robot now and take me instead. I have a bicycle with like 6 gears.

I first put it in the lightest gearing. One peddle is on top. I put all my weight on the pettle and it will go down rapidly, move me off the line quickly, but won't take me far distance wise.

Now same situation, but in highest gear. Again I step on the peddle with all my weight, so the power that is used is the same.
Now the peddle will go down slowly, probably gives me a faster speed (for that one half cycle: peddle up-> down) and it will definitely cover more distance.
Since no energy gets lost. Do I get it right, since you said that before, that in this example, acceleration is (still) the same?

I mean, just like in your example "If they put an overall equal energy, but the longer geared bike will take more time to accelerate, then we are not taking about the same power. The robots have not equal power."
But they do have equal power. I use my same body weight on the peddle in both situations. And on a bicycle I am the power supply.

But you'll probably reply with "no, you don't have the same power". I'm guessing. So how is that then?

 

[roost]

Okay okay, let me disect that part. I DO understand what you are saying here.
Now are you also saying that both these rockets have the same acceleration?

Let me give you a real life exampple and then maybe you can explain.

Forget the robot now and take me instead. I have a bicycle with like 6 gears.

I first put it in the lightest gearing. One peddle is on top. I put all my weight on the pettle and it will go down rapidly, move me off the line quickly, but won't take me far distance wise.

Now same situation, but in highest gear. Again I step on the peddle with all my weight, so the power that is used is the same.
Now the peddle will go down slowly, probably gives me a faster speed (for that one half cycle: peddle up-> down) and it will definitely cover more distance.
Since no energy gets lost. Do I get it right, since you said that before, that in this example, acceleration is (still) the same?

I mean, just like in your example "If they put an overall equal energy, but the longer geared bike will take more time to accelerate, then we are not taking about the same power. The robots have not equal power."
But they do have equal power. I use my same body weight on the peddle in both situations. And on a bicycle I am the power supply.

But you'll probably reply with "no, you don't have the same power". I'm guessing. So how is that then?

No, I never said they have the same acceleration.

You are mixing stuff.
Your weight on the pedals is NOT making power. Your weight and the pedals are making power.
Ok, lets make an example:
Say you weight 80kg
The bike weights 20Kg
The diameter of the pedal (from top to bottom position) is 40cm = 0,4m
So you step on the pedal and make it rotate prom top to bottom. You are converting your potential energy into motion. You are not using muscle power during the down stroke, to not complicate things.

The calculation is this: Wp= m*g*h = 80Kg * 9,81m/s^2 * 0,4m = 314 J of energy (work) that your bodyweight has given.
Lets say that the efficiency of the transmission is 100%, so all the energy is converted into kinetic energy of the bike and you (motion).

If the bike is set on short gear, lets say it takes 2 sec until your foot comes from TDC of pedal to BDC. So it converts the all potential energy given into kinetic in 2s.
That is 314 J/ 2 s = 157W
The pedals and bodyweight system was working with 157Watts of power!

If the bike is set on long gear, lets say it takes 5 sec until your foot comes from TDC of pedal to BDC. So it converts the all potential energy given into kinetic in 5s.
That is 314 J/ 5 s = 63W
The pedals and bodyweight system was working with 63Watts of power!!!!

Can you understand now where is the difference? You didn't have the same power!!

Speed:
On both cases the final kinetic energy of bike was 314 J.
Wk = (mt*v^2)/2
v = SquareRoot((Wk*2)/mt)
v= SquareRoot((314*2)/100)
v= 2,5m/s
The final speed will be always the same, not caring if you thake 2s or 10years on the downstroke.


Yes the two bikes accelerated differently, bcoz one had 157W of power and the other 63W.

But the two scooter engine has the same power if it working at lets say 13000rpm, not caring about the lenght of the fianl gear ratio.

 

[Folkert@MinaRally]

No, I never said they have the same acceleration.

Hmm I thougt that was all this discussion about. Of course I'll probbaly now mixing scooters, with the bike. But didn't you say that with the different gears, they still had same acceleration.
So they don't.

If the bike is set on short gear, lets say it takes 2 sec until your foot comes from TDC of pedal to BDC. So it converts the all potential energy given into kinetic in 2s.
That is 314 J/ 2 s = 157W
The pedals and bodyweight system was working with 157Watts of power!

If the bike is set on long gear, lets say it takes 5 sec until your foot comes from TDC of pedal to BDC. So it converts the all potential energy given into kinetic in 5s.
That is 314 J/ 5 s = 63W
The pedals and bodyweight system was working with 63Watts of power!!!!

Can you understand now where is the difference? You didn't have the same power!!

I understand that yes. But it (at least) LOOKS as if you are caculating the OUTput power, which is difference, where as the INput power (the biker standinf on the peddles and the peddles themselves) is the same.
Don't even dare to say it anymore: right?

Yes the two bikes accelerated differently, bcoz one had 157W of power and the other 63W.

Yeah different output power.
But that probably goes for the scooters as well, since when both have same cilinder, timing, exhuast etc, their input (fuel/air mixture which hold the potential energy) is the same, I'm guessing.

But the two scooter engine has the same power if it working at lets say 13000rpm, not caring about the lenght of the fianl gear ratio.

Yeah same power, I totally agree, but not same acceleration (sorry), just like with the bikes, one is faster to a certain point.....

I guess when both scooter have same power input, like in the bikes, their power output is different, which then would do mean different acceleration, dependable by the gearing.

Or am I now just totally off again? (you can just say yes or no)

 

[roost]

Hmm I thougt that was all this discussion about. Of course I'll probbaly now mixing scooters, with the bike. But didn't you say that with the different gears, they still had same acceleration.
So they don't.

I was talking about the space probes, sorry for not specify that.

I understand that yes. But it (at least) LOOKS as if you are caculating the OUTput power, which is difference, where as the INput power (the biker standinf on the peddles and the peddles themselves) is the same.
Don't even dare to say it anymore: right?

I dont understand what are you trying to say. Do you mean the power on the pedals vs. the power on the wheel? Well, that has to be equal if thansmission has no looses.

Yeah different output power.
But that probably goes for the scooters as well, since when both have same cilinder, timing, exhuast etc, their input (fuel/air mixture which hold the potential energy) is the same, I'm guessing.

To, the scooter is making the same ammount of work per second (=power) all the time.

Yeah same power, I totally agree, but not same acceleration (sorry), just like with the bikes, one is faster to a certain point.....

I guess when both scooter have same power input, like in the bikes, their power output is different, which then would do mean different acceleration, dependable by the gearing.

If the scooters have the same "input", and the "output" on the wheel is different with different final gears, then where did it go that difference of energy? In a black hole maybe?

Well, explain me then this:
If you measure on a dyno the power of an manualshift bike, why would it measure always the same power output, no matter in which gear the engine is? (it really does it!)

 

[Folkert@MinaRally]

(......)

If the scooters have the same "input", and the "output" on the wheel is different with different final gears, then where did it go that difference of energy? In a black hole maybe?

Roost, I presume(d) there's energy loss due to friction (heat) in the variator assembly (of course this goes for both scooters in this example, where we said they have same tranny setup) but then, the different final gearing is where energy is also lost. At least, as I was always told, on this board(!) that shorter (too short) gearing, gives a useless waste of energy, due to unwanted friction (no straight meshing) and overrev (the shorter geared scooter will rev the same as the higher geard, but because of the short gearing, that RPM is overrev (out of powerband) for one).

So that was my idea behind it.

Well, explain me then this:
If you measure on a dyno the power of an manualshift bike, why would it measure always the same power output, no matter in which gear the engine is? (it really does it!)

So it does? I guess I wasn't aware, but it does make me wonder, I have seen lot's of dyno graphs in bike mags (Performance Bikes mainly) and they do put out different power per gear. Of course it's only in the final gear that the Max. power output is measured.

I do agree that the engine power output is always the same, but that the shorter the gearing, more power is lost through the gearbox. So while crank power would always be the same then, rear wheel power wouldn't. Guess that is not the case then.
But a motorbike that is kept in 1st gear can't, have the same rearwheel power as one that is run up to 6th gear(?)

 

[Mr Matrix]

Here is one of my Rieju RS2 Matrix with an Hebo Manston Replica.
You only see 3 to 6 gear there. (6 gear AM6 @ 15/48 )

Mvh M

 

[roost]

Roost, I presume(d) there's energy loss due to friction (heat) in the variator assembly (of course this goes for both scooters in this example, where we said they have same tranny setup) but then, the different final gearing is where energy is also lost. At least, as I was always told, on this board(!) that shorter (too short) gearing, gives a useless waste of energy, due to unwanted friction (no straight meshing) and overrev (the shorter geared scooter will rev the same as the higher geard, but because of the short gearing, that RPM is overrev (out of powerband) for one).

So that was my idea behind it.

This is partly true.
Different gear sets can't have big differences in power consumption. Well, the friction of the teeth on different gears is little bit different, but the ammount of difference is very small, detectable maybe by very precise instruments in laboratory conditions.
Overrev is not a waste of energy. But because of overrev there is less energy made by the engine (because of the much worse cylinder scavenging).

So it does? I guess I wasn't aware, but it does make me wonder, I have seen lot's of dyno graphs in bike mags (Performance Bikes mainly) and they do put out different power per gear. Of course it's only in the final gear that the Max. power output is measured.

I do agree that the engine power output is always the same, but that the shorter the gearing, more power is lost through the gearbox. So while crank power would always be the same then, rear wheel power wouldn't. Guess that is not the case then.
But a motorbike that is kept in 1st gear can't, have the same rearwheel power as one that is run up to 6th gear(?)

I never or maybe rarely seen dyno graph of all gears. However the higher the gear the more accurate the results.

 

[Folkert@MinaRally]

^^

Maybe I'm worng and it was thrust curves. I'll check again. Since you also state that the different energy loses between different gears is very small, maybe I have looked at other graphs, then power output graphs.

While I think about that last statement of mine: "But a motorbike that is kept in 1st gear can't, have the same rearwheel power as one that is run up to 6th gear(?)"
I'm like: hmm it could have the same power at the rear wheel, but the power is just used for different things: in lowest/lower gears to get more torque to get it off the line and go hard to the redline, and in other gears to give top end power. At least so I guess now. Since other bikes are geared to have a nice "midrange".

I do know by now, it's more complicated then it looks. There's so much "physics" going on etc.

 

[Joël]

^^
While I think about that last statement of mine: "But a motorbike that is kept in 1st gear can't, have the same rearwheel power as one that is run up to 6th gear(?)"
I'm like: hmm it could have the same power at the rear wheel, but the power is just used for different things: in lowest/lower gears to get more torque to get it off the line and go hard to the redline, and in other gears to give top end power. At least so I guess now. Since other bikes are geared to have a nice "midrange".

I do know by now, it's more complicated then it looks. There's so much "physics" going on etc.

The terms "top end power" and "midrange" are used for the engine, not the gearing.
It says something about the amount of power over the rev scale, not over the driving speed scale.

But, you are thinking in the right direction, a lower gear is used for big wheel torque (low wheel rpm) to rev fast to the max. power rpm.
And a higher gear is used for a high wheel rpm (low torque) to get a high topspeed.

That's in fact the essence of a gearbox, the max. output power remains the same but you can differ wheel torque and wheel rpm to get the proper performance.

 

[Folkert@MinaRally]

The terms "top end power" and "midrange" are used for the engine, not the gearing.
It says something about the amount of power over the rev scale, not over the driving speed scale.

But, you are thinking in the right direction, a lower gear is used for big wheel torque (low wheel rpm) to rev fast to the max. power rpm.
And a higher gear is used for a high wheel rpm (low torque) to get a high topspeed.

That's in fact the essence of a gearbox, the max. output power remains the same but you can differ wheel torque and wheel rpm to get the proper performance.

Yeah true, I know "top end power" and "midrange" are terms for the revrange. So yeah I used it wrongly here.

For the "right thinking" part. Isn't that basically what the whole thing was about? low gearing for more torque (to have quick(er) acceleration) and higher gearing for more top speed.
That's what we also do when changing the final gearing in scooter, aren't we? We trade in some acceleration (well this is not the case when going from stock gearing to straigh-cut teeth) but when already an aftermarket gearing is installed and we would upgrade to even higher/taller gearing, we are going to trade off (some) acceleration, for more top speed.
Of course engine output stays the same, it's in the scooters gearbox where we can control the amount of torque, since this is a gearbox, only with fixed ratio's.

 

[Hans F.]

Of course engine output stays the same, it's in the scooters gearbox where we can control the amount of torque, since this is a gearbox, only with fixed ratio's.

but when you'r driving 20km/h with a long gearing, of 20km/h with a shorter gearing you have the same power on the rearwheel, and the same rotation speed, so you also have the same torque
(in case of a cvt system off course )

 

[wiwirast]

Next year I'm going for 200 kph with 2 2f4r,2 hr4 ect.And a lot of money offcourse.

 

[emo]

Next year I'm going for 200 kph with 2 2f4r,2 hr4 ect.And a lot of money offcourse.

what the fu..?? are you trying to tell here??

 

[Browni]

what the fu..?? are you trying to tell here??

I think he will build a duble engine 2fast bike!! ?

 

[Folkert@MinaRally]

but when you'r driving 20km/h with a long gearing, of 20km/h with a shorter gearing you have the same power on the rearwheel, and the same rotation speed, so you also have the same torque
(in case of a cvt system off course )

That would be the case with same wheel+tyre diameter.

Now what if one scooter has a 13" wheel and the other a 10".

To go 20km/h the smaller wheel has to spin faster to reach the same speed.
So this would also mean a different amount of torque @ the rear wheel. At least that is what sounds logic (to me)

 

[Hans F.]

that's very simple, off course the smaller wheel has to rotate faster, at the same speed, with the same power. So the torque on the rear axle is lower.

But you don't need a torque to accelerate, but a force pushing you forward. To get a force pushing you forward, you've got to have a force wich is pushing bachward.
The torque of the 10" wheel is lower, but also it's diameter is smaller. F=m.a
The force is stil the same as the force of the bigger wheel.

An easyer way of looking at wheel diameters is by seeing them as an integral part of the reduction case.

 

[Joël]

For the "right thinking" part. Isn't that basically what the whole thing was about? low gearing for more torque (to have quick(er) acceleration) and higher gearing for more top speed.
That's what we also do when changing the final gearing in scooter, aren't we? We trade in some acceleration (well this is not the case when going from stock gearing to straigh-cut teeth) but when already an aftermarket gearing is installed and we would upgrade to even higher/taller gearing, we are going to trade off (some) acceleration, for more top speed.
Of course engine output stays the same, it's in the scooters gearbox where we can control the amount of torque, since this is a gearbox, only with fixed ratio's.

Folkert, first look at my drawing again.

Yes, you have faster acceleration but only till the point of maximum power!!!!
When that point is passed, it doesn't matter if you have a RF of 10 or 1000.

Because the VARIATOR UNIT COMPENSATES the final gearing from that point.

If you still don't understand send me a PM then I'll explain it in dutch.

 

[Folkert@MinaRally]

Folkert, first look at my drawing again.

Yes, you have faster acceleration but only till the point of maximum power!!!!
When that point is passed, it doesn't matter if you have a RF of 10 or 1000.

Because the VARIATOR UNIT COMPENSATES the final gearing from that point.

If you still don't understand send me a PM then I'll explain it in dutch.

Joël, I'm aware of that. Maybe I'm just explaining it wrongly or too difficult.

My point was that Roost said that acceleration is always the same.

I was just trying (and only) to say, like you say, one has faster acceleration, but up to a certain point of course (the max. power point). Since the shorter geared scooter reaches max. power sooner, it stops accelerating. That's when the longer geared scooter passes it (And continues accelerating, untill it has also reached max. power)

I understand that at that point, it doesn't matter what RF you run. (they both stop accelerating, since they don't make any more power to overcome (more) drag/road friction etc.)
So acceleration would be the same (as in zero) or is that not the case?

(okay that's my final say, if I'm still (way) off I'll PM you).

 

[Joël]

I was just trying (and only) to say, like you say, one has faster acceleration, but up to a certain point of course (the max. power point). Since the shorter geared scooter reaches max. power sooner, it stops accelerating. That's when the longer geared scooter passes it (And continues accelerating, untill it has also reached max. power)

It doesn't stop accelerating when it reaches max power, in fact the acceleration is at its greatest at that point!!
You only stop accelerating when the produced power equals the load, also called your "topspeed".
Then all the power is used to MAINTAIN the speed, and there is nothing left to accelerate to a higher speed.
And even if the shorter geared one stops accelerating, you can't say the longer geared one passes it, it will run in. (maybe that's what you meant)

 

[Folkert@MinaRally]

It doesn't stop accelerating when it reaches max power, in fact the acceleration is at its greatest at that point!!
You only stop accelerating when the produced power equals the load, also called your "topspeed".
Then all the power is used to MAINTAIN the speed, and there is nothing left to accelerate to a higher speed.
And even if the shorter geared one stops accelerating, you can't say the longer geared one passes it, it will run in. (maybe that's what you meant)

Pass or run in? I think we mean the same. I mean, since the shorter geared scooter won't go as fast, the other scooter will run in and inventually pass it. It has to, other wise it wouldn't go faster.

For that first part, I see a little contradiction: First you say it will not stop accelerating @ max power, the acceleration is the greatest at that point.
Then you say: Then all that power (the max power) is used to keep (maintain) that speed, and there is nothing left to acclerate to a higher speed.
So (how I read it) you say: accleration is greatest at max power AND at max power ("all that power is used..") to maintain top speed -> so no more accelerating. (?)

I ttoally agree with that second part, and is what I said (or at least was trying to). Max power means, it can't produce any more power, so it can't overcome any more load/friction/drag (it's equaled out - thrust vs. drag) so it stops accelerating. And of course, that's the top speed.