Panther G setup for decent reliability - newcomer questions

[Kaelis]

So the choice is just Taigen or Tamiya, got it.

Max-U52, that Jagdpanther sounds great, particularly the engine, makes me even more excited about IBU2. Though the cannon sound is rather quiet, but i guess thats just a matter of messing a bit with the sound samples.

The thing about the 3:1 gearboxes is the low torque. With low torque you'll have trouble turning the tank. The 4:1 gives good scale speed yet you can still turn the thing around tight corners. If you want more speed get motors rated for higher rpm. The stock 380s are rated at 18,000 rpm (no-load).

That sounds like the difference between 3:1 and 4:1 is really big, 'trouble turning the tank' is bad news... I was under the impression that 4:1 simply gives 33% more torque at the cost of 33% speed compared to 3:1, is that not correct?

One thing i didnt notice previously is that the 3:1 gearbox on rctank.de is paired with 13,000 rpm motors, while 4:1 apparently has 18,000 rpm motors, so i guess the loss of speed from lower gearing would be negated by higher motor rpm. Question is, do the different rpm motors have varied torque as well? If not, then there is just no reason to choose the 3:1-13,000rpm offering?

On the other hand, i did more research on the motors - turns out not only there are quite a few options to pick from, some of them are even available in my country. No Promax unfortunately, which seems to be the recommended brand, but plenty of Graupner and Traxxas, among many other brands. And they are really cheap too, cheap enough to experiment with them, but i guess i still need to do more research on which ones are a good idea...

It does seem like with multiple motor options 4:1 would be the perfect choice, provided there was an option to just get higher rpm motors if i wanted more speed. However, i have been unable to find anything faster than the stock 18,000 rpm. On top of that, ive stumbled upon this video of Jagdpanther running on 3:1 gearbox with 480 motors:
https://www.youtube.com/watch?v=gYOrSdBcFZQ
from this thread:
http://www.rcgroups.com/forums/showthread.php?t=1467342
Looks like a perfect combination to me, enough power and plenty of available top speed, maybe even a tad too speedy!

Sorry about all this drivel, hope its at least somewhat coherent... Would really appreciate some insight here, starting to get a bit lost now with all the options, considerations and unknowns

[Max-U52]

Getting lost is easy to do, especially when you start educating yourself about motors. I've been going down that road the last year or two, and the amount of info to be absorbed is amazing. I'll try to hit most of your questions and issues. First, as I understand it, torque in an electric motor is pretty much the same throughout so the real difference is rpm. What I mean is, unlike a gas car engine where you have a torque curve, electric motors don't have that curve and torque is constant from minimum to maximum power. The way I understand it.

Second, and this is VERY important, don't relate "3:1" and "4:1" to any actual gear ratio. These are totally mis-applied terms used by manufacturers to make it easy to identify gearboxes and make them more marketable. The 4 shaft do reduce top speed but it's not an actual 4:1 or 3:1 ratio so you can't relate them to each other on that basis, as you do when you say 4:1 gives 33% more ... That would be true if those were the actual ratios of the gearboxes, but they're not. Yes, I'd like to pinch whoever got that can of worms open in the first place.

Anyway, I still recommend the 4:1 for WWII tanks and the only tanks I run 3:1 in are the M41 and the ZTZ-99A because they actually had that kind of top speed. I did some time trials (videos on my youtube channel) and got the 99A to a scale speed of about 45 mph, which is very close to the actual claimed speed of 80 kph for the real tank. If I get an Abrams I'll probably run the faster GBs there, too. Remember, on it's best day, on a glass smooth autobahn, with a little downhill slope, an actual Tiger might hit 25 mph. The Panthers were a bit faster but rarely ran at top speed due to the high risk of breakdown under those conditions. If your tank can cover 82 feet in 15 seconds it's moving at a scale 60 mph, which almost no tank actually reaches. I said almost, I know the Hellcat can and they say the M1 but those are governed for about 45.

With the IBU and the TPA you can adjust the sound for cannon and engine to get the balance you like, but I agree the cannon could use a bit more volume. I'm in the process of tuning in the TPA in the Jagdtiger, and the Jagdpanther will be next.

Enough for now.

[Max-U52]

Oh yeah, I looked at the JP in your video and first, at the beginning they show brass dual ratio gearboxes so I don't know why they say 3:1, and second, most of that is done on cement, and you're gonna find they turn a LOT different on a grippy surface like grass or carpet or even damp dirt.

[Max-U52]

Here, watch this video and you might get some info about turning and how different GBs effect that. My JP now turns fine on the carpet because I went to the IBU2, but it's performance on stock was very similar to what you'll get with "3:1" gearboxes.

[Kaelis]

Alright, even more confusion!

Now i realize that the easiest route would be to just take the tested and reliable 4.1, and i thank you for bearing with me here. But the thing is, i dont care that much about having the most historically accurate top speed - in fact, after watching various videos i decided im not very happy with that top speed. Which is why im trying to find out if its at all possible to get different options for rpm/torque by having different motors, and if so then which gearbox would be the best fit for that.

So first off, i guess i just need to find out what exact gear ratio those Taigen gearboxes have. After more digging ive discovered that these 'ratios' are actually the number of reduction gears, though that information in itself is pretty much meaningless for our purposes. However, ive also found a thread where someone calculated the actual ratios - supposedly the Taigen 3.1 is something like 40:1 while the 4.1 is 90:1. That is indeed a huge difference.

Now the motors... with brushless its easy, for every different motor you have the number of turns specified - more turns, more torque and less rpm. And usually also the exact rpm per volt. But nothing of that sort for these brushed motors, well at least nothing about torque. No idea if its proportional to max rpm or not, is it linear, logarithmic... heck, for all i know two different motors could have a static torque regardless of max rpm. And then theres the fact that it has to fit to the gearbox and into the hull... How does one go about picking a motor without this info?

As for the video i linked, the gearbox they used is in fact simply labeled as 3:1 by the manufacturer/distributor... And around the middle of the video it drives uphill on grass, seems to be doing fine, or is that not enough?

As for your video frankly i dont know what kind of conclusion i should make from it I mean, too many variables, would need to know the specifics of each setup - what kind of gearbox (real ratios!), suspension, motors, boards etc... i dont even know how exactly does superspin work and when does it engage!

[MichaelC]

Kaelis,

I think you should wait til your tank shows up and see what kind of speed, motors and gearbox it has and go from there. Otherwise you might end up getting more than you need and yet still not get what you really want out of the tank speed. My understanding is that the 4:1 and 3:1 is basically the number of gears between the motor pinion and the drive shaft gear. In practice, it really doesn't mean much since you could have large gears going to smaller gears, or smaller gears going to large gears. So unless the intermediary gear sizes are identical, 4:1 or 3:1 means nothing.

On the motor RPM....... Unless you know exactly what you gearbox gear ratios are, this again is useless. Even if you do, the RPM on the specs are with no load, so when you put load on the motor, a supposedly 13,000 RPM could still end up running faster than a 18,000 RPM spec motors. The quality of the motor (number of wire loops ?) will determine the actually torque or RPM under load.

Once you got your tank, you can run it and see what it is that you like to make better. i.e. If you want it faster but is happy with the gearbox, then get faster motor. If you like the motors, but want it to go slower, then keep the motors and get a higher ratio gearbox and hope that it will slow the tank down.

My whole point is that there is all kinds of motors and gearbox out there and it all depends on what you want your tank to do at the end. It is very difficult to speculate motors. RPMs, gear ratios, torque without a starting point.

[Kaelis]

MichaelC, you are of course right, but the thing is i have to pick the right gearbox from the outset, as the gearboxes are just too expensive to experiment with them. I do know the ratios (as mentioned in my last post, will confirm with the vendor), so its just a matter of finding out if i have any motor options for higher torque or rpm.

I guess ill make a thread in the Electronics sections, as my questions are now specific to just motors.