Limitless AMPS VS MASS

[Diem Turner]

They are sold out everywhere here right now...pp is great for testing I imagine, I want to try it out on 8s swb also...it'll bee needed to push car past 162mph on 8s safely...I just wish castle would come out with a 500a mmx8s so I don't need xlx2 for everything..it's so damn big in a plastic chassis car..I wanna push the plastic chassis arrma into the rest of the 325mm cars far as low voltage speed..I believe it's very capable of 150/4s an 165/5s by useing a lighter setup..Shaun didn't have drivetrain issues till the 150s running an heavier 6s setup..spool an c-shaft where his issues....Noone has pushed this platform to its limits yet......I belive it'll blow some minds in the near future..to run 130with 1 an 142 with 2 cheap packs 4s is amazing,an the logs are just as impressive

Oh I have no doubts about the potential of the platform. You and Shawn have both done amazing things with it.

Oh and...here ya go
https://amz.run/65GR

 

[K-BASH]

Oh I have no doubts about the potential of the platform. You and Shawn have both done amazing things with it.

Oh and...here ya go
https://amz.run/65GR

On sale tooo..

 

[Diem Turner]

On sale tooo..

Didn't these things used to cost 49.95? Inflation FTW.

 

[joshludden]

That's awesome bro. I would expect a noticeable difference between two cars where one weights 2.5lbs more than the other. That's a big ol' chunk of mass.

Yeah, I think I'm going to be ordering a PP module soon too. I feel like my trigger pull is pretty good at this point, but if you want to make some objective comparisons, it's necessary to remove as many variables as possible and your trigger finger is the most unreliable component that, as a compounding factor, has the largest influence on key parameters like amp draw and voltage sag.

Nb4

 

[Diem Turner]

Nb4

I like the fact that the NB4 has that feature integrated. Great move on their part. But I'm not swapping out my Futaba gear when I can just add that function to my current setup for $75. Yes, I could sell my Futaba stuff and buy an NB4 and have lots of money left over, but I love my 7PXR and don't see myself moving to anything else, anytime soon. There's just something about the way it feels. Perhaps if I come across someone at some point that has an NB4 and can try it out before I buy it and discover that it's better than what I have. I'm not averse to having my mind changed. But at this point, I'm three elbows deep into Futaba.

 

[ABabyEater]

Imo nb4 >>> pp, since the perfect pass intercepts and interferes with signals from the receiver, whereas the nb4 just broadcasts a smooth signal from the transmitter. No hokey signal interceptor to go wrong mid-run.

 

[Diem Turner]

Imo nb4 >>> pp, since the perfect pass intercepts and interferes with signals from the receiver, whereas the nb4 just broadcasts a smooth signal from the transmitter. No hokey signal interceptor to go wrong mid-run.

I've never seen a hokey signal interceptor go wrong mid-run. I'm not saying it can't happen, I've just never seen it.

 

[ABabyEater]

I've never seen a hokey signal interceptor go wrong mid-run. I'm not saying it can't happen, I've just never seen it.

I haven't seen it in a while, but I have seen pp fail. Lucky for the driver, they caught it being "glitchy" pre-run and stopped. Admittedly, this is super early in the perfect pass production lifetime and could be a complete non-issue at this point.

As for signal interference, it is similar to using a gyro. Plenty of people are fine speedrunning with a gyro, but many, myself included, can feel the interference it gives in steering, and choose to go without it, for comfort, peace of mind, or because they just don't like it.

Kinda like how 1:1 performance cars greatly reduce, if not disable, traction control when placed into sport/race/track mode (vehicle depending).

 

[LibertyMKiii]

I would say that you will see the weight difference shows itself most in the 0-120 mph acceleration. At a certain point, aerodynamics is the key factor that is stopping the car from going faster.

The vendetta is a smaller car and will cut through the air better all things (shape of the body) being equal.

I might play around with a 3s platform car next year for aerodynamics. Hopefully, by then someone can get the center shaft all worked out and I'd love to see metal CVD axles.

 

[Diem Turner]

I haven't seen it in a while, but I have seen pp fail. Lucky for the driver, they caught it being "glitchy" pre-run and stopped. Admittedly, this is super early in the perfect pass production lifetime and could be a complete non-issue at this point.

As for signal interference, it is similar to using a gyro. Plenty of people are fine speedrunning with a gyro, but many, myself included, can feel the interference it gives in steering, and choose to go without it, for comfort, peace of mind, or because they just don't like it.

Kinda like how 1:1 performance cars greatly reduce, if not disable, traction control when placed into sport/race/track mode (vehicle depending).

Now that I think about it, I've heard about one glitching out before but, if memory serves, I think the unit had taken some damage from a crash. Anyways, it's a risk I'm willing to take because, as stated above, I'm not in the market to swap out all of my radio gear. At least not at present.

As for gyros, I was against using them for quite some time as well. I did like the behavior of Spektrum's AVC initially for bashing but was put off by how the gyros acted on the RC6GS and GT5 so I stopped using a gyro altogether. I tried the SkyRC GC-401 but that was totally sub-par. I had bought a Futaba GYC-441 but didn't install it for several months. I installed it two months ago and I've been pleasantly surprised by how natural it feels. I have the gain on it turned waaaay down so it doesn't really even do all that much when speed running. I just feel like it helps just a tiny bit with tracking. The gyro very much seems to follow the old mantra of "you get what you pay for".

 

[LibertyMKiii]

As for gyros, I was against using them for quite some time as well. I did like the behavior of Spektrum's AVC initially for bashing but was put off by how the gyros acted on the RC6GS and GT5 so I stopped using a gyro altogether. I tried the SkyRC GC-401 but that was totally sub-par. I had bought a Futaba GYC-441 but didn't install it for several months. I installed it two months ago and I've been pleasantly surprised by how natural it feels. I have the gain on it turned waaaay down so it doesn't really even do all that much when speed running. I just feel like it helps just a tiny bit with tracking. The gyro very much seems to follow the old mantra of "you get what you pay for".

I had tried the futaba gyro on the VTE2 and ultimately didn't trust it. The car was having death wobbles at 70+ speeds. (likely I still had it turned up too high)
Removed it and never looked back. The car drives just fine without a gyro and has some 30+ speed runs with zero crashes (knock on wood).

 

[Hector_Fisher]

Okay, so i understand the concept that reduced weight will give better acceleration, but I'm not following how it would have an affect on top speed. At speed, a car has 3 limitations: aerodynamic drag, drivetrain/rolling resistance, and battery capabilities. The drag equation doesn't have a variable for "mass". But the force equation (F=ma) does. If you remove weight from a car (let's say you replaced all fasteners with titanium or whatever) you would have faster acceleration, not higher top speed. Aerodynamic profile or properties of the car haven't changed (unless you want to argue that it's now sitting 0.XX mm higher and that affects it's top speed), and the lesser rolling resistance on the bearings due to the lighter weight is IMO negligible. So i'm leaning towards this being a battery capability thing.

Perhaps you could argue the trade off is that a lighter battery would give you faster acceleration with less energy required (meaning fewer watts) and therefore less voltage sag on those lighter batteries. And this might be applicable for shorter speed run locations (trying for 150mph in 1500ft). At least that's the principle. Though, if you have a long enough run way, the principle should lean towards what Liberty stated that larger and heavier batteries should always increase performance. But that's all a discussion of battery capabilities, not weight--meaning two batteries with the same weight and one might perform better than the other.

But perhaps that's the point of the discussion, that road lengths are limited and so acceleration matters? If i'm wrong, then what am I missing here?

 

[LibertyMKiii]

Okay, so i understand the concept that reduced weight will give better acceleration, but I'm not following how it would have an affect on top speed. At speed, a car has 3 limitations: aerodynamic drag, drivetrain/rolling resistance, and battery capabilities. The drag equation doesn't have a variable for "mass". But the force equation (F=ma) does. If you remove weight from a car (let's say you replaced all fasteners with titanium or whatever) you would have faster acceleration, not higher top speed. Aerodynamic profile or properties of the car haven't changed (unless you want to argue that it's now sitting 0.XX mm higher and that affects it's top speed), and the lesser rolling resistance on the bearings due to the lighter weight is IMO negligible. So i'm leaning towards this being a battery capability thing.

Perhaps you could argue the trade off is that a lighter battery would give you faster acceleration with less energy required (meaning fewer watts) and therefore less voltage sag on those lighter batteries. And this might be applicable for shorter speed run locations (trying for 150mph in 1500ft). At least that's the principle. Though, if you have a long enough run way, the principle should lean towards what Liberty stated that larger and heavier batteries should always increase performance. But that's all a discussion of battery capabilities, not weight--meaning two batteries with the same weight and one might perform better than the other.

But perhaps that's the point of the discussion, that road lengths are limited and so acceleration matters? If i'm wrong, then what am I missing here?

That is spot on. Of course, the speed run with RC cars is limited to our vision, road length, and radio signal capabilities. Acceleration is a factor and weight will play a part in this.

In very general terms, only 2 things hurt our ability to go faster.... aerodynamic drag and power.

In my eyes, weight is a minor factor not worth considering too much. The power-to-weight ratio on these cars is absolutely insane and for considerations of top speed won't be a factor.

Example:

Corvette C5 base - 3247 lbs / 345hp = 9.41 lbs per hp
22' Suzuki Hyabusa - 582 lbs / 188 hp = 3.09 lbs per hp
1/7 scale RC producing 10kw - 14 lbs / 11kW (13.4hp) = 1.04 lbs per hp
1/7 scale RC producing 18kW - 15 lbs / 18kW (24.12 hp) = 0.625 lbs per hp

 

[Diem Turner]

That is spot on. Of course, the speed run with RC cars is limited to our vision, road length, and radio signal capabilities. Acceleration is a factor and weight will play a part in this.

In very general terms, only 2 things hurt our ability to go faster.... aerodynamic drag and power.

In my eyes, weight is a minor factor not worth considering too much. The power-to-weight ratio on these cars is absolutely insane and for considerations of top speed won't be a factor.

Example:

Corvette C5 base - 3247 lbs / 345hp = 9.41 lbs per hp
22' Suzuki Hyabusa - 582 lbs / 188 hp = 3.09 lbs per hp
1/7 scale RC producing 10kw - 14 lbs / 11kW (13.4hp) = 1.04 lbs per hp
1/7 scale RC producing 18kW - 15 lbs / 18kW (24.12 hp) = 0.625 lbs per hp

Agreed. That's my assessment as well. The power to weight ratios on modern 1/7 scale cars is, as you said, insane. Neither the 13hp nor the 24hp motor is going to notice the removal or addition of a half pound or even a pound in total weight (especially not if we're talking about the addition of a second battery which will alleviate voltage sag which, by its very nature, will result in a higher top speed). At least not when it comes to speed running. I can see where it could make a difference when drag racing as you're trying to overcome the mass of the vehicle at rest and bring it up to speed as fast as possible. But when you're taking 6-8 seconds to reach WOT, I can't see how it would matter.

 

[Hector_Fisher]

HOWEVER, maybe something I wasn't considering:

A lighter truck (overall weight, such as plastic chassis, etc) would accelerate faster. OR in other words, the lighter truck would require less power to achieve the same rate of acceleration as the heavier truck. Thereby, less amp draw and thereby less voltage sag if using the same set of batteries for both trucks. While voltage sag could be mitigated with a longer and steady squeeze of the trigger (or PP) on the heavier truck, again you run into the issue of WOT for 6 to 8 seconds and the thing is basically gone.

This may circle back to the idea of running out of room, but I can see where managing voltage sag under acceleration (by reducing weight and thus strain on the batteries) would pay dividends for the few seconds after your acceleration begins to plateau. Particularly since this isn't a fuel driven 1:1 where you have peak power until you run out of gas--every second you drive the RC the max potential voltage drops. If you've taken a bigger power draw on the batteries due to the heavier weight, and they are still recovering, those few seconds afterwards may be the difference in having the extra voltage to achieve a higher speed.

Consider my position revised.

 

[LibertyMKiii]

HOWEVER, maybe something I wasn't considering:

A lighter truck (overall weight, such as plastic chassis, etc) would accelerate faster. OR in other words, the lighter truck would require less power to achieve the same rate of acceleration as the heavier truck. Thereby, less amp draw and thereby less voltage sag if using the same set of batteries for both trucks. While voltage sag could be mitigated with a longer and steady squeeze of the trigger (or PP) on the heavier truck, again you run into the issue of WOT for 6 to 8 seconds and the thing is basically gone.

This may circle back to the idea of running out of room, but I can see where managing voltage sag under acceleration (by reducing weight and thus strain on the batteries) would pay dividends for the few seconds after your acceleration begins to plateau. Particularly since this isn't a fuel driven 1:1 where you have peak power until you run out of gas--every second you drive the RC the max potential voltage drops. If you've taken a bigger power draw on the batteries due to the heavier weight, and they are still recovering, those few seconds afterwards may be the difference in having the extra voltage to achieve a higher speed.

Consider my position revised.

There is some small element of this. I think if the 3s line had a uber-strong driveline we would see some more impressive numbers with them...

Get your 1:1 car up to around 90 to 100mph on the highway and hold your hand out flat to the wind. Aero drag is the biggest hindrance of speed at speeds of 120+

When I rode motorcycles you could feel a difference at 140+ mph and the acceleration suddenly slowed drastically. The same holds true for rc cars. Going over 140 requires significant power.

 

[Hector_Fisher]

Get your 1:1 car up to around 90 to 100mph on the highway

@LibertyMKiii are you suggesting I should BREAK THE LAW?????

**NSA_Agent35 is now following you**

 

[LibertyMKiii]

@LibertyMKiii are you suggesting I should BREAK THE LAW?????

**NSA_Agent35 is now following you**

I don't always suggest breaking the law, but when I do it always involves going fast.

 

[Jerold]

K-Bash is correct. The car weight does make a difference... In theory.

Less weight means less power required and less current. Less current is always good. However, I believe the real problem is the down force because just like drag, it increase with speed. Which means even if you loss a pound off your car you will probably generate more down force with the higher speed and reduce the effectiveness of your car diet. For referece Formula 1 cars generate 5X the weight of the car in down force, but they need to turn.

If you want to get the car on a diet remove all the wing and have minimal down force. I did an experiment with and without the rear wing. On 4S with the wing I go something like 81 MPH, without the wing I got like 85mph.

If you want to lower your current then increase your voltage. There is an advantage to this because it means lower resistance, less heat and smaller wires. It's generally it's more efficient but requires higher voltage components.

 

[LibertyMKiii]

K-Bash is correct. The car weight does make a difference... In theory.

Less weight means less power required and less current. Less current is always good. However, I believe the real problem is the down force because just like drag, it increase with speed. Which means even if you loss a pound off your car you will probably generate more down force with the higher speed and reduce the effectiveness of your car diet. For referece Formula 1 cars generate 5X the weight of the car in down force, but they need to turn.

If you want to get the car on a diet remove all the wing and have minimal down force. I did an experiment with and without the rear wing. On 4S with the wing I go something like 81 MPH, without the wing I got like 85mph.

If you want to lower your current then increase your voltage. There is an advantage to this because it means lower resistance, less heat and smaller wires. It's generally it's more efficient but requires higher voltage components.

I did something similar when trying to push a stock electronics Kraton 6s to top speeds.
With a wing it went 94 and without it went 96, but was very unstable during braking. I'm sure with more power it would have been impossible to control. The downforce is a necessary evil for traction needs to accelerate at these crazy rates we need with little grip.