Walt

iTrader: (2)

I was just as baffled, but I think I've got it now... I was thinking: "It's impossible to have multiple gears with the same gear pitch have different tooth counts but the same OD."

I still think I'm right with that statement. The problem with my assumption was that all the gears DO NOT have the same gear pitch. HPI (and others I guess) have decided to hold the OD constant, and change the pitch (and tooth shape) as necessary to make it work.

Now then, there have to be limitations and compromises here... they probably can't push this much further than they have (there probably won't be a 14 tooth pinion coming out in the future, for example), and there is probably increased noise, vibration and wear with the slightly mismatched gear teeth profiles, but noise, vibration and wear are not really issues here.

In my opinion, the bennifits of being able to pick any ratio and to be able to change gears without having to reposition the engine far outweight whatever drawback this is going to cause... I think it's a great idea... I'd love to give credit to whoever came up with it. They were thinking 'outside the box.' When I was in Mechanical Engineering school and took a gear design class it was just hammered into my head that the pitches had to be the same, and this defined the OD for a given number of teeth, etc. I probably never would have thought to do this otherwise, but I'm glad someone else did.

BossPlaya

thanks Harry for the response, appreciate it.

My local LHS is very good at stocking HPI parts and this car just flat out sounds good so I'm seriously considering getting one asap and most likely a new engine along with it. Though, I might wait for the version with aluminum shocks, front one way, bigger tank etc... if such a thing is even going to be released; I'm assuming it is.

I think a big part of the attraction to this car for me, not forgetting how its been said to perform obviously, but also all the talk of how easy it is to adjust and to drive, since im a newbie.

boom

iTrader: (10)

Walt,

Holding OD (pitch diameters) constant... you will NEVER be able to change ratios..... you can go from a 10/20 to a 100/200 by changing diametric pitch and not pitch diameter but in the end you ratio is still the same. You have not changed your torque/veloctiy output..... you have only made you system more efficient by going to finer teeth gears.

I know you know all this..... but I just want to bring it back out to you before you write it off.

Walt

iTrader: (2)

I think you might be confusing OD and pitch diameter (I did the same thing)... I know they are not the same... this would have more credibility if I could remember how pitch diameter is calculated, but I don't... I'll check my old engineering books here on my shelf, but I think that book is back at home.

The ratio is certainly the number of pinion teeth over the number of spur teeth, but I think it's also the pinion pitch diameter over the spur pitch diameter, and if that's true, then the pitch diameters must be changing even though the overall OD is staying the same.

Walt

iTrader: (2)

Just remembered... I've got my trusty Bosch Automotive Handbook here...

pitch diameter (d) = z * m

Where: z = the number of teeth
m = 'modul'

m = d/z, where 'd' in this case is the reference diameter and z is still the number of teeth... ok, so what is the 'reference diameter?' Well, it looks like Bosch assumes we know this. There is a picture shown, and the reference diameter is clearly shown as being different from the overall OD, but it doesn't go into that detail... will probably need a gear design text book to go any further into this, if necessary...

But I'm pretty happy at this point.. OD constant, pitch diameter and tooth count vary.

popsracer

Guys;

The Diameter of the Pinion/Spur is irrelevant. It is the Tooth count that determines Ratio.

Diameter is only a factor in NON-toothed applications, such as "V"-belt drives or as in Tire diameter.

The reason that you can get away with this Variable Meshing, is the Gears are designed to handle considerably more Horsepower than would ever be possible in the Chassis design.
With a finer tooth pitch such as 64P, none of this would be possible.

Walt

iTrader: (2)

Yes... overall diameter is irrelevant, as you said, but the 'pitch diameter' is important... it's another way to figure out the ratio, but it HAS to be proportional to the number of teeth in a gear drive system. The confusion is between overall diameter, pitch diameter, number of teeth and tooth pitch (shape)... define any three of those and the fourth can be calculated. In HPI's case, they 'defined' the OD to be a constant, and then varied the number of teeth and tooth pitch (shape) to be able to get various ratios that work together with a constant center to center distance... ingenious (although perhaps not an idea HPI came up with).

boom

iTrader: (10)

Are you suggesting they're meshing different pitches together?

Consider this example.... a certain 10 to 20 tooth combo has X center distance..... keeping that center distance you can (1) hold the pitch... and change teeth to 15/15... (2) hold the ratio.. and change the pitch..... 100/200 (3) mix match pitch/teeth#...... 10 teeth high module gear meshed with a 2000 teeth super low module gear.....

Are you saying HPI is doing case 3? I can see how it could work if the module were not to vary by too much.

InitialD

So you must be running normal clutch shoes instead of a Centax then... I thought you claimed that you had all the hop ups available for the Impulse...

nitrodude

iTrader: (8)

Yokomo alredy does this on the GT4, 3 year old car. You can change the pinions without changing the mesh. You can even run different split between the pinons and the spurs, for example, you can run a 15 18 conbo on the pinions, and a 48-46 split on the spurs. I prefer this arrangement as it gives you more gearing options, and you can run almost any conbo of pinions and spurs, unlike, lets say the NTC3, on which you can only run a preset set of gears together.

All yokomo did was change teh shape of the teeth on the pinions. The smaller pinions, like a 15th, have more pointy teeth, whereas the bigger pinions, like a 20th, have shorter and blunter teeth.

Thanks,

Steven Muller
MPP

popsracer

Guys;

You really don't even need these new design gears to run different splits. The 1M Gears on older Cars have more than enough beef to handle the less than perfect mesh. (at least in 1/10th scale)

No matter what the Diameter, Pitch, Pitch diameter, etc of the Gears, it is the number of Teeth that determine the ratio, Period.

You can have an R/C Car gear set with a 17/49 ratio, and a Machine Gear set that is 3 ft in diameter with giant Teeth and a 17/49 ratio. The reduction will still be the same 2.88 to 1.

eddiethefish

OK guys,

One of the secret hopups on Atsushi's R40 has recently been revealed. Check it out!

fastharry™

iTrader: (4)

I have a centax on my veteq and Impulse.....

and your point is what?..

boom

iTrader: (10)

Yes the teeth defines the ratio, that's also because the teeth defines the pitch diameter... and that defines the leverage ratio (like pulleys). Using your example of the RC car gear 17/49 and huge machine gear 17/49..... putting the RC 17 and the machine 49 together will get you a numerical ratio of 2.88 to 1..... but the pitch diameter ratio will be a lot higher.. because the machine 49 gear is 3 feet in diameter.. compared to the RC 49 which I arbitrarily say is 3 inch in dia......... the gearing is affectively "shorter" than the RC17 to RC49 combo.......... BUT ... big BUT... that's if you can get the RC 17 to mesh with the machine 49 to mesh to begin with.

So once again the teeth defines the ratio..... ONLY if..... the diametric pitch (gear pitch) of the combination is identical or close to that.

popsracer

boom;

My point (and what People seem to be confused about) is that no Matter what, the number of Teeth on each Gear is solely what determines the ratio.
What HPI has done, is modify Pitch slightly to keep the outside diameter of the Gears the same, so Gears with different tooth counts will can be used without having to loosen the Motor and re-adjust mesh.

I was trying to state this in a simpler way, but maybe I was unsuccessful.