fastest lst???
12-17-2007, 09:58 PM
#52
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RE: fastest lst???
ok here it is who ever was doubting that trucks cant go fast revo doing 73 mph dont believe me see it your self im a speed demon i might just aswell cancel my supermaxx project and check how fast my lst2 can go 
http://www.youtube.com/watch?v=KRtiP7vRK3c
http://www.youtube.com/watch?v=KRtiP7vRK3c
12-17-2007, 10:34 PM
#53
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RE: fastest lst???
ORIGINAL: full maxx
thank the great rc god that someone else understands ... if you dont get it then hand over your transmitter cause you dont need to be driving
thank the great rc god that someone else understands ... if you dont get it then hand over your transmitter cause you dont need to be driving
12-17-2007, 11:42 PM
#54
RE: fastest lst???
ORIGINAL: RenegadeRevo
LOL... you're the one not getting it. Your claim is that you can't get any faster than the tri-engine Kyosho (see post #27 and my reference to it in post #45) My rebuttal is that adding more engines is not the answer to top speed... creating more rotational speed is.... gearing or otherwise. HP and TQ numbers don't have anything to do with actual top speed. It has something to do with being able to push it to top speed and sustaining it, but the physical limitations to only being able to spin the wheels at a certain velocity is what you're not grasping. Take a stock Revo for example. The box says it's capable of over 40MPH. Due to gearing and power/weight ratios, the TRX 2.5r has a rough time getting it all the way to 40MPH. That is your argument, if more HP/TQ is applied, then the gearing can change, which is 100% accurate. My argument is that even with a gear change, if you drop the RPM level too low, the top speed will suffer... Yes, I am in agreement with you that if you add more HP, you are CAPABLE of producing more speed by changing gearing, but it is not the HP/TQ that allows for the top speed, it is the rotational velocity that allows it to move faster.
My examples were to isolate just increasing the HP/TQ output of the power plant. I understand the gearing changes, etc... When I changed my Revo over from the 2.5r to the TM323, I realized a HUGE accelleration increase, however it seemed it topped out at a slower speed. Even though it had almost twice the power, it did not go any faster. That is the effect of adding HP/TQ to it. It does nothing for top speed, and can actually decrease the top speed if a lower revving engine is put on there. Now, that allowed me to increase my gear ratio, which then increased my top speed, but it was the rotational velocity change (final drive ratio) that caused me to gain a higher top speed, not the horsepower. RPM's are RPM's, and unless the final drive ratio changes, you won't see an increase in top speed just by adding a bigger engine. There is a direct effect to increasing the RPM range of the motor... an indirect effect of adding HP/TQ to the motor....
Now, if you don't understand the physics behind making a vehicle go faster, I can not drill it into your head. You are assuming that the power/weight ratio is impossible to beat... however the triple engine may be worth less than it seems. If you have enough horsepower and torque to get the vehicle to speed, adding more isn't going to do anything but get it topped out faster. The Revo only weighs in at 9 lbs... it doesn't take THAT much power to get a 9lb Revo to speed. If you designed the truck to ONLY break speed records, there could be a lot of weight-saving upgrades to do to get it to the 8lb and lower range. With a Novarossi 528x, modded correctly and the correct pipe, (or similar engine) you should be able to get enough HP/TQ and enough RPM's (the real big part) to get it to 100MPH. The wind resistance, drag, and controlablility would have to be addressed, however with off-the-shelf parts, the drivetrain can be built to get it to that speed.
ORIGINAL: robwiljas
You still just don't get it. You're assuming the use of the same final drive ratio for both engines in your example which is rediculous. The higher hp engine will use a higher gear ratio. Lets say engine 1 has 19.05hp at 10000rpm (10lb-ft of torque). With the 4:1 drive ratio the wheels will be spinning at 2500rpm with 40lb-ft of torque. Now lets say engine 2 has 25hp at 5000rpm (23.81lb-ft of torque ) and a 1.68:1 drive ratio. Engine 2 will still have the wheels spinning with 40lb-ft of torque, but at 2976rpm, which means it will be going faster. I don't know how I can make it any clearer, but I'm done arguing with both of you.
Edit: I missed your last post
First... obviously you don't.
Second... When you gear the engine that high, you reduce the torque at the wheels. If the revo where held in the air, sure the wheels would be spinning 104mph (minus a little for drag). As soon as you put it on the ground, the engine would not have the power to get up to 50000rpm because it's geared too high for the weight of the Revo.
Anyway I'm done, believe what you want to believe.
You still just don't get it. You're assuming the use of the same final drive ratio for both engines in your example which is rediculous. The higher hp engine will use a higher gear ratio. Lets say engine 1 has 19.05hp at 10000rpm (10lb-ft of torque). With the 4:1 drive ratio the wheels will be spinning at 2500rpm with 40lb-ft of torque. Now lets say engine 2 has 25hp at 5000rpm (23.81lb-ft of torque ) and a 1.68:1 drive ratio. Engine 2 will still have the wheels spinning with 40lb-ft of torque, but at 2976rpm, which means it will be going faster. I don't know how I can make it any clearer, but I'm done arguing with both of you.
Edit: I missed your last post
ORIGINAL: RenegadeRevo
First off, I know plenty about horsepower and torque.... I also understand the basics of physics and rotating masses.
Second... I am pretty sure...
would provide a different feeling than your "Edit"... your post was that there is NO WAY (read it verbatim) a monster truck can go 80MPH. I can show you numbers that will prove that theory wrong... Fairly quickly too... a Traxxas Revo running the wide ratio gear set with a 20T clutch bell and a 35T spur gear with 7" tires and a 50,000 RPM engine has the possibility of 104MPH. Has it been done? Not that I know of... but all it takes is someone with a bank roll that wants to prove a theory.
First off, I know plenty about horsepower and torque.... I also understand the basics of physics and rotating masses.
Second... I am pretty sure...
There is no way you're getting a nitro monster truck, let alone an LST2, to go 80mph. The worlds fastest R/C monster truck is a brushless wheely king with touring car tires, which ran 72.9mph. The worlds fastest nitro car is a tripple .21 kyosho evola and only runs 88mph. Now if three .21 engines will only propel that relatively light car to 88mph, how do you expect an LST2 to do 80mph? A twin engine Savage X ran 59.6mph.
First... obviously you don't.
Second... When you gear the engine that high, you reduce the torque at the wheels. If the revo where held in the air, sure the wheels would be spinning 104mph (minus a little for drag). As soon as you put it on the ground, the engine would not have the power to get up to 50000rpm because it's geared too high for the weight of the Revo.
Anyway I'm done, believe what you want to believe.
My examples were to isolate just increasing the HP/TQ output of the power plant. I understand the gearing changes, etc... When I changed my Revo over from the 2.5r to the TM323, I realized a HUGE accelleration increase, however it seemed it topped out at a slower speed. Even though it had almost twice the power, it did not go any faster. That is the effect of adding HP/TQ to it. It does nothing for top speed, and can actually decrease the top speed if a lower revving engine is put on there. Now, that allowed me to increase my gear ratio, which then increased my top speed, but it was the rotational velocity change (final drive ratio) that caused me to gain a higher top speed, not the horsepower. RPM's are RPM's, and unless the final drive ratio changes, you won't see an increase in top speed just by adding a bigger engine. There is a direct effect to increasing the RPM range of the motor... an indirect effect of adding HP/TQ to the motor....
Now, if you don't understand the physics behind making a vehicle go faster, I can not drill it into your head. You are assuming that the power/weight ratio is impossible to beat... however the triple engine may be worth less than it seems. If you have enough horsepower and torque to get the vehicle to speed, adding more isn't going to do anything but get it topped out faster. The Revo only weighs in at 9 lbs... it doesn't take THAT much power to get a 9lb Revo to speed. If you designed the truck to ONLY break speed records, there could be a lot of weight-saving upgrades to do to get it to the 8lb and lower range. With a Novarossi 528x, modded correctly and the correct pipe, (or similar engine) you should be able to get enough HP/TQ and enough RPM's (the real big part) to get it to 100MPH. The wind resistance, drag, and controlablility would have to be addressed, however with off-the-shelf parts, the drivetrain can be built to get it to that speed.
By the way I know that 100HP in a 5Lb car and these gear ratios are rediculous, I'm just trying to show you that even with more than enough horsepower, an increase of just 1hp is faster.
12-18-2007, 01:16 AM
#56
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RE: fastest lst???
ORIGINAL: robwiljas
You know I said I wouldn't argue anymore but I can't not respond to you. You're supporting my argument and you don't even know it. You still have it in your head that engine RPM means speed, and it doesn't. RPM at the wheels means speed, but the RPM of the engine means nothing, horsepower does. When you put the TM523 in your truck you increaded the HP, but you HAVE to gear it correctly to take advantage of it. I'm sure you know that it takes torque at the wheels to move a vehicle, and if enough torque is not at the wheels the the vehicle will slow down (like trying to drive a manual car up a steep hill at 20mph in 5th gear). Now the torque required is increased as you go faster but let's pretend for the sake of making this simpler for you to understand that it doesn't. Imagine that a 5lb scale R/C vehicle requires a constant 5lb-ft of torque at the wheels to keep it at speed. Now Imagine you could invent a .21 engine that has 100HP at 35000RPM (15lb-ft of torque) and another engine that has 101HP at 1000RPM (530.25lb-ft of torque). Obviosly both engines produce more than enough power to propel a 5lb R/C vehicle, and according to your argument the 100HP 35000RPM engine would make the car faster because of it's RPM. That's not true though. If you gear the 35000RPM engine at a ratio of 1:3 then you would be putting the required 5lb-ft of torque to the wheels, at 105000rpm. Now take the 101HP 1000RPM engine and gear it at a ratio of 106.05:1. Again you'd be putting the required 5lb-ft of torque to the wheels, but at 106050RPM. The 101HP engine would be spinning the wheels faster and the car would be faster. As I said before horsepower is just a mathamatical representation for torque x rpm. If you increase the RPM while keeping the torque the same, the horsepower is increased, but if you increase the RPM while keeping the HP the same, the torque is decreased. It is a very simple concept, I don't know what is it that you don't understand about it?
By the way I know that 100HP in a 5Lb car and these gear ratios are rediculous, I'm just trying to show you that even with more than enough horsepower, an increase of just 1hp is faster.
ORIGINAL: RenegadeRevo
LOL... you're the one not getting it. Your claim is that you can't get any faster than the tri-engine Kyosho (see post #27 and my reference to it in post #45) My rebuttal is that adding more engines is not the answer to top speed... creating more rotational speed is.... gearing or otherwise. HP and TQ numbers don't have anything to do with actual top speed. It has something to do with being able to push it to top speed and sustaining it, but the physical limitations to only being able to spin the wheels at a certain velocity is what you're not grasping. Take a stock Revo for example. The box says it's capable of over 40MPH. Due to gearing and power/weight ratios, the TRX 2.5r has a rough time getting it all the way to 40MPH. That is your argument, if more HP/TQ is applied, then the gearing can change, which is 100% accurate. My argument is that even with a gear change, if you drop the RPM level too low, the top speed will suffer... Yes, I am in agreement with you that if you add more HP, you are CAPABLE of producing more speed by changing gearing, but it is not the HP/TQ that allows for the top speed, it is the rotational velocity that allows it to move faster.
My examples were to isolate just increasing the HP/TQ output of the power plant. I understand the gearing changes, etc... When I changed my Revo over from the 2.5r to the TM323, I realized a HUGE accelleration increase, however it seemed it topped out at a slower speed. Even though it had almost twice the power, it did not go any faster. That is the effect of adding HP/TQ to it. It does nothing for top speed, and can actually decrease the top speed if a lower revving engine is put on there. Now, that allowed me to increase my gear ratio, which then increased my top speed, but it was the rotational velocity change (final drive ratio) that caused me to gain a higher top speed, not the horsepower. RPM's are RPM's, and unless the final drive ratio changes, you won't see an increase in top speed just by adding a bigger engine. There is a direct effect to increasing the RPM range of the motor... an indirect effect of adding HP/TQ to the motor....
Now, if you don't understand the physics behind making a vehicle go faster, I can not drill it into your head. You are assuming that the power/weight ratio is impossible to beat... however the triple engine may be worth less than it seems. If you have enough horsepower and torque to get the vehicle to speed, adding more isn't going to do anything but get it topped out faster. The Revo only weighs in at 9 lbs... it doesn't take THAT much power to get a 9lb Revo to speed. If you designed the truck to ONLY break speed records, there could be a lot of weight-saving upgrades to do to get it to the 8lb and lower range. With a Novarossi 528x, modded correctly and the correct pipe, (or similar engine) you should be able to get enough HP/TQ and enough RPM's (the real big part) to get it to 100MPH. The wind resistance, drag, and controlablility would have to be addressed, however with off-the-shelf parts, the drivetrain can be built to get it to that speed.
ORIGINAL: robwiljas
You still just don't get it. You're assuming the use of the same final drive ratio for both engines in your example which is rediculous. The higher hp engine will use a higher gear ratio. Lets say engine 1 has 19.05hp at 10000rpm (10lb-ft of torque). With the 4:1 drive ratio the wheels will be spinning at 2500rpm with 40lb-ft of torque. Now lets say engine 2 has 25hp at 5000rpm (23.81lb-ft of torque ) and a 1.68:1 drive ratio. Engine 2 will still have the wheels spinning with 40lb-ft of torque, but at 2976rpm, which means it will be going faster. I don't know how I can make it any clearer, but I'm done arguing with both of you.
Edit: I missed your last post
First... obviously you don't.
Second... When you gear the engine that high, you reduce the torque at the wheels. If the revo where held in the air, sure the wheels would be spinning 104mph (minus a little for drag). As soon as you put it on the ground, the engine would not have the power to get up to 50000rpm because it's geared too high for the weight of the Revo.
Anyway I'm done, believe what you want to believe.
You still just don't get it. You're assuming the use of the same final drive ratio for both engines in your example which is rediculous. The higher hp engine will use a higher gear ratio. Lets say engine 1 has 19.05hp at 10000rpm (10lb-ft of torque). With the 4:1 drive ratio the wheels will be spinning at 2500rpm with 40lb-ft of torque. Now lets say engine 2 has 25hp at 5000rpm (23.81lb-ft of torque ) and a 1.68:1 drive ratio. Engine 2 will still have the wheels spinning with 40lb-ft of torque, but at 2976rpm, which means it will be going faster. I don't know how I can make it any clearer, but I'm done arguing with both of you.
Edit: I missed your last post
ORIGINAL: RenegadeRevo
First off, I know plenty about horsepower and torque.... I also understand the basics of physics and rotating masses.
Second... I am pretty sure...
would provide a different feeling than your "Edit"... your post was that there is NO WAY (read it verbatim) a monster truck can go 80MPH. I can show you numbers that will prove that theory wrong... Fairly quickly too... a Traxxas Revo running the wide ratio gear set with a 20T clutch bell and a 35T spur gear with 7" tires and a 50,000 RPM engine has the possibility of 104MPH. Has it been done? Not that I know of... but all it takes is someone with a bank roll that wants to prove a theory.
First off, I know plenty about horsepower and torque.... I also understand the basics of physics and rotating masses.
Second... I am pretty sure...
There is no way you're getting a nitro monster truck, let alone an LST2, to go 80mph. The worlds fastest R/C monster truck is a brushless wheely king with touring car tires, which ran 72.9mph. The worlds fastest nitro car is a tripple .21 kyosho evola and only runs 88mph. Now if three .21 engines will only propel that relatively light car to 88mph, how do you expect an LST2 to do 80mph? A twin engine Savage X ran 59.6mph.
First... obviously you don't.
Second... When you gear the engine that high, you reduce the torque at the wheels. If the revo where held in the air, sure the wheels would be spinning 104mph (minus a little for drag). As soon as you put it on the ground, the engine would not have the power to get up to 50000rpm because it's geared too high for the weight of the Revo.
Anyway I'm done, believe what you want to believe.
My examples were to isolate just increasing the HP/TQ output of the power plant. I understand the gearing changes, etc... When I changed my Revo over from the 2.5r to the TM323, I realized a HUGE accelleration increase, however it seemed it topped out at a slower speed. Even though it had almost twice the power, it did not go any faster. That is the effect of adding HP/TQ to it. It does nothing for top speed, and can actually decrease the top speed if a lower revving engine is put on there. Now, that allowed me to increase my gear ratio, which then increased my top speed, but it was the rotational velocity change (final drive ratio) that caused me to gain a higher top speed, not the horsepower. RPM's are RPM's, and unless the final drive ratio changes, you won't see an increase in top speed just by adding a bigger engine. There is a direct effect to increasing the RPM range of the motor... an indirect effect of adding HP/TQ to the motor....
Now, if you don't understand the physics behind making a vehicle go faster, I can not drill it into your head. You are assuming that the power/weight ratio is impossible to beat... however the triple engine may be worth less than it seems. If you have enough horsepower and torque to get the vehicle to speed, adding more isn't going to do anything but get it topped out faster. The Revo only weighs in at 9 lbs... it doesn't take THAT much power to get a 9lb Revo to speed. If you designed the truck to ONLY break speed records, there could be a lot of weight-saving upgrades to do to get it to the 8lb and lower range. With a Novarossi 528x, modded correctly and the correct pipe, (or similar engine) you should be able to get enough HP/TQ and enough RPM's (the real big part) to get it to 100MPH. The wind resistance, drag, and controlablility would have to be addressed, however with off-the-shelf parts, the drivetrain can be built to get it to that speed.
By the way I know that 100HP in a 5Lb car and these gear ratios are rediculous, I'm just trying to show you that even with more than enough horsepower, an increase of just 1hp is faster.
12-18-2007, 01:18 AM
#57
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RE: fastest lst???
ORIGINAL: robwiljas
With something called a transmission, look it up. 
ORIGINAL: full maxx
one more question ...how do you gear an engine
one more question ...how do you gear an engine
12-18-2007, 02:10 AM
#58
RE: fastest lst???
ORIGINAL: RenegadeRevo
Why is it that you just don't get what I'm saying? You are telling me what I'm telling you...thus proving MY point... when you increase the rotational velocity of the drivetrain, the top speed will increase. Rotational velocity is NOT directly effected by horsepower, PERIOD. Yes, indirectly, you can increase horsepower and effectively re-gear the drivetrain and gain a higher top speed, HOWEVER... if you simply increase the HP, you will NOT see an increase of top speed. We're talking about the idea of DIRECT effects, not indirect. No matter how many times you argue the same point, you can not ONLY increase HP in a vehicle to gain top speed.... you must increase the rotational velocity by putting in taller gearing... HOWEVER, increasing the RPM limit of the engine will produce DIRECT results. PERIOD. It's pure physics... SO, the fact that the car has 3 engines is irrelevant except for allowing the possibility for gear changes... and honestly, if I really wanted to put money into a truck that was built for ONLY top speed runs, I could get a Revo past the 80MPH mark... easily.... however I don't have the money to blow on such a project.
Why is it that you just don't get what I'm saying? You are telling me what I'm telling you...thus proving MY point... when you increase the rotational velocity of the drivetrain, the top speed will increase. Rotational velocity is NOT directly effected by horsepower, PERIOD. Yes, indirectly, you can increase horsepower and effectively re-gear the drivetrain and gain a higher top speed, HOWEVER... if you simply increase the HP, you will NOT see an increase of top speed. We're talking about the idea of DIRECT effects, not indirect. No matter how many times you argue the same point, you can not ONLY increase HP in a vehicle to gain top speed.... you must increase the rotational velocity by putting in taller gearing... HOWEVER, increasing the RPM limit of the engine will produce DIRECT results. PERIOD. It's pure physics... SO, the fact that the car has 3 engines is irrelevant except for allowing the possibility for gear changes... and honestly, if I really wanted to put money into a truck that was built for ONLY top speed runs, I could get a Revo past the 80MPH mark... easily.... however I don't have the money to blow on such a project.
12-18-2007, 06:42 AM
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RE: fastest lst???
no matter if it's by increasing torque or increasing RPM, BOTH INCREASE HORSEPOWER................rpm has nothing to do with horsepower... rpm ...once again is HOW FAST AN ENGINE WILL ROTATE NOT HOW MUCH POWER IT PUTS OUT AND AS A MATTER OF FACT THE HIGHER THE RPM GETS THE MORE THE TORQUE IS REDUCED AFTER A CERTAIN POINT AND THATS BEFORE REDLINE/MAX RPM... SOMETHING LIKE 7O -75 % OF THE RPM RANGE AFTER THAT THE TORQUE STARTS TO DROP OFF ... maybe this word will help ... POWERBAND and you cannot increase torque before you increase horsepower ... horsepower makes torque ... torque DOES NOT make horsepower... torque is a result of horsepower at a given rpm ... when you change rpm you change torque also however horsepower stays the same
12-18-2007, 06:56 AM
#60
RE: fastest lst???
ORIGINAL: full maxx
no matter if it's by increasing torque or increasing RPM, BOTH INCREASE HORSEPOWER................rpm has nothing to do with horsepower... rpm ...once again is HOW FAST AN ENGINE WILL ROTATE NOT HOW MUCH POWER IT PUTS OUT AND AS A MATTER OF FACT THE HIGHER THE RPM GETS THE MORE THE TORQUE IS REDUCED AFTER A CERTAIN POINT AND THATS BEFORE REDLINE/MAX RPM... SOMETHING LIKE 7O -75 % OF THE RPM RANGE AFTER THAT THE TORQUE STARTS TO DROP OFF ... maybe this word will help ... POWERBAND and you cannot increase torque before you increase horsepower ... horsepower makes torque ... torque DOES NOT make horsepower... torque is a result of horsepower at a given rpm ... when you change rpm you change torque also however horsepower stays the same
no matter if it's by increasing torque or increasing RPM, BOTH INCREASE HORSEPOWER................rpm has nothing to do with horsepower... rpm ...once again is HOW FAST AN ENGINE WILL ROTATE NOT HOW MUCH POWER IT PUTS OUT AND AS A MATTER OF FACT THE HIGHER THE RPM GETS THE MORE THE TORQUE IS REDUCED AFTER A CERTAIN POINT AND THATS BEFORE REDLINE/MAX RPM... SOMETHING LIKE 7O -75 % OF THE RPM RANGE AFTER THAT THE TORQUE STARTS TO DROP OFF ... maybe this word will help ... POWERBAND and you cannot increase torque before you increase horsepower ... horsepower makes torque ... torque DOES NOT make horsepower... torque is a result of horsepower at a given rpm ... when you change rpm you change torque also however horsepower stays the same
[link]http://en.wikipedia.org/wiki/Horsepower[/link]
[link]http://web-cars.com/math/horsepower.html[/link]
[link]http://www.howstuffworks.com/horsepower.htm[/link]
Do you need more?
12-18-2007, 07:55 AM
#61
RE: fastest lst???
Ok, I'm going to prove this once and for all...
We all know a Revo 3.3 can do 45mph, so we're going to use this as an example. Here are the specs of a stock Revo 3.3. Please note this does not account for tire ballooning, which will add a little speed, thus why I used 40mph in this example instead of 45mph which is Traxxas claimed top speed.
Top speed in MPH: 40mph
Differential Ratio: 2.8461538461538462
Transmission Ratio: 2.111111111111111
Spur Tooth Count: 38
Clutch Bell Count: 15
Tire Diameter (inches): 5.9
Total Ratio: 15.22165 : 1
Tire Circumference: 18.535 inches (470.799 mm)
Required Motor RPM: 34688.365 RPM
Ok, that's pretty easy, but Traxxas doesn't post the HP rating of the 3.3, so for this example we're going to pretend that it's 2.0HP at 35000RPM. It doesn't matter that it's not exact.
I've already told you that HP is just a mathematical equation for torque x RPM (and the links I provided in my last post prove that as well), so if we do the math of 5250/35000*22=.03 That means the engine is producing .3lb-ft of torque at 35000RPM. Since this is such a small number it's easier to convert it to oz-in, which would be 57.6oz-in of torque.
Now that we estimate the engine is producing 57.6oz-in of torque, we calculate the torque at the wheels using the total gear ratio that we know is 15.22165:1, so at 40mph, we estimate there is 876.77oz-in of torque at the wheels (57.6*15.22165=876.76704).
Now we're going to sideline for a moment so I can make sure you understand torque. 1oz-in of torque means you can move 1oz of weight, a distance of 1". 10oz-in means you can move 10oz of weight a distance of 1", or 5oz of weight a distance of 2", or 20oz of weight a distance of 1/2". See how that works? It is directly proportional, If you reduce the torque, you MUST either reduce the weight, or reduce the distance. This is simple physics. If you don't believe me, please read about torque [link=http://en.wikipedia.org/wiki/Torque]here[/link].
Ok, so now that we know that, and we know that the Revo above has 876.77oz-in of torque at the wheels at 40mph, what happens if we reduce the torque? You must either reduce the weight of the Revo, or reduce the distance? Still follow me? Yet again this is simple physics.
Ok now lets test your theory on RPM. Lets take the engine out of the Revo and add a 2.0HP 50000RPM engine. Since we have increased the RPM of the engine, but not increased the horsepower, this engine has less torque. Doing the math again we find that this engine is only producing .21lb-ft of torque (5250/50000*2=.21), or 40.32oz-in of torque at 50000RPM.
Now again we figure out the torque at the wheels using the gear ratio (40.32*15.22165=613.736928), so the torque at the wheels is now 613.74oz-in of torque.
Remember that rule that if you decrease the torque, you MUST either decrease the weight or the distance? Well assuming both motors weigh the same, we haven't lost any weight, so we must decrease the distance. We can no longer travel 40 miles in one hour. If you do the math you will realize that you have lost 30% of your speed, (613.74/876.77=.0.700001141). This is not completely accurate because engines have a power curve and will be producing a different torque at that RPM, but you get the point. The Revo is now going significantly slower.
The reason this has happened is because the revo is now severely over-geared, and the engine does not have enough torque to get it's RPM's up. If you change your gear ratio to 21.74:1 though, you will again have 876oz-in of torque at the wheels, and will again be going 40mph.
Adding RPM without adding horsepower has done nothing, except require you to re-gear. The same thing would happen if you added torque without adding horsepower (lower RPM). In order to increase speed, you must increase the horsepower. If you still can't grasp that concept, then I'm sorry but there's nothing more for me to say, you just can't grasp simple physics.
We all know a Revo 3.3 can do 45mph, so we're going to use this as an example. Here are the specs of a stock Revo 3.3. Please note this does not account for tire ballooning, which will add a little speed, thus why I used 40mph in this example instead of 45mph which is Traxxas claimed top speed.
Top speed in MPH: 40mph
Differential Ratio: 2.8461538461538462
Transmission Ratio: 2.111111111111111
Spur Tooth Count: 38
Clutch Bell Count: 15
Tire Diameter (inches): 5.9
Total Ratio: 15.22165 : 1
Tire Circumference: 18.535 inches (470.799 mm)
Required Motor RPM: 34688.365 RPM
Ok, that's pretty easy, but Traxxas doesn't post the HP rating of the 3.3, so for this example we're going to pretend that it's 2.0HP at 35000RPM. It doesn't matter that it's not exact.
I've already told you that HP is just a mathematical equation for torque x RPM (and the links I provided in my last post prove that as well), so if we do the math of 5250/35000*22=.03 That means the engine is producing .3lb-ft of torque at 35000RPM. Since this is such a small number it's easier to convert it to oz-in, which would be 57.6oz-in of torque.
Now that we estimate the engine is producing 57.6oz-in of torque, we calculate the torque at the wheels using the total gear ratio that we know is 15.22165:1, so at 40mph, we estimate there is 876.77oz-in of torque at the wheels (57.6*15.22165=876.76704).
Now we're going to sideline for a moment so I can make sure you understand torque. 1oz-in of torque means you can move 1oz of weight, a distance of 1". 10oz-in means you can move 10oz of weight a distance of 1", or 5oz of weight a distance of 2", or 20oz of weight a distance of 1/2". See how that works? It is directly proportional, If you reduce the torque, you MUST either reduce the weight, or reduce the distance. This is simple physics. If you don't believe me, please read about torque [link=http://en.wikipedia.org/wiki/Torque]here[/link].
Ok, so now that we know that, and we know that the Revo above has 876.77oz-in of torque at the wheels at 40mph, what happens if we reduce the torque? You must either reduce the weight of the Revo, or reduce the distance? Still follow me? Yet again this is simple physics.
Ok now lets test your theory on RPM. Lets take the engine out of the Revo and add a 2.0HP 50000RPM engine. Since we have increased the RPM of the engine, but not increased the horsepower, this engine has less torque. Doing the math again we find that this engine is only producing .21lb-ft of torque (5250/50000*2=.21), or 40.32oz-in of torque at 50000RPM.
Now again we figure out the torque at the wheels using the gear ratio (40.32*15.22165=613.736928), so the torque at the wheels is now 613.74oz-in of torque.
Remember that rule that if you decrease the torque, you MUST either decrease the weight or the distance? Well assuming both motors weigh the same, we haven't lost any weight, so we must decrease the distance. We can no longer travel 40 miles in one hour. If you do the math you will realize that you have lost 30% of your speed, (613.74/876.77=.0.700001141). This is not completely accurate because engines have a power curve and will be producing a different torque at that RPM, but you get the point. The Revo is now going significantly slower.
The reason this has happened is because the revo is now severely over-geared, and the engine does not have enough torque to get it's RPM's up. If you change your gear ratio to 21.74:1 though, you will again have 876oz-in of torque at the wheels, and will again be going 40mph.
Adding RPM without adding horsepower has done nothing, except require you to re-gear. The same thing would happen if you added torque without adding horsepower (lower RPM). In order to increase speed, you must increase the horsepower. If you still can't grasp that concept, then I'm sorry but there's nothing more for me to say, you just can't grasp simple physics.
12-18-2007, 01:27 PM
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RE: fastest lst???
Despite the fact that there is some good info in this thread, it is becoming close to a flame war and is now way off topic. Therefore, I am locking it down.
