Speed run 10 sec duration motor KV choice

[LibertyMKiii]

Speed junkie here checking in, I don't seem to care about anything else.
I would like the RC to run down to the starting point of the run, make a full speed pass and drive back to me.

In this scenario of a 10 sec run, not taking into account the application, weight, load etc.... What would be the harm in going double the KV from the "norm" of low 800-1300 kv on 8s. To something like a D wind 2600-3200 kv in a 58 series motor.

My thoughts are that Higher KV motors can do more with each volt. Heat is the obvious concern, but I feel that a 10sec run the motor will likely survive. Data logs show my 33V runs drop to as low as 25V under load at 320+ amps.

For now the system is 8s in the 300-400 amp range.

Thanks in advance for any help/advice.

-Liberty

[RaceMechaniX]

You can try and run this, but chances are you will hit a wall with your ESC. Doubling the kv will more than double your current. The number of ESC's that can push 400A for 10Sec can be counted on one hand.
Let's just assume you have a 1000A ESC and the best batteries in the world. If your prop unloads you will overspeed the 58 series motor in a heartbeat and BOOM!

The TP 58 series are not good choices for high RPM SAW runs. The TP4070CM is a better choice.

[Fluid]

Uh, 2600-3200 is not double 800-1300. A 1600-1800 Kv motor on 8S is much more doable. But, what hull is the OP intending to run? How long is the pond? What are his speed goals? How fast has he run an FE boat?


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[Speed3]

Double the kV is 4 times the amp draw. The amp draw squares in proportion to the kV increase ratio. You mention your batteries was as low as 25v and you were seeing 320 plus amps. Those batteries will not be up for 4 times more amps if you are going from 1300 to 2600kv.

Secondly the shalf and coupler will be under a lot more load. They may not be able to hold together under that load.

The other issue do you have a boat that is able to handle that power.

Like fluid said 1600 to 1800kv is more doable on 8s.

[LibertyMKiii]

Thanks for the info. I was not aware of the specific correlation between kv and amp draw.

My question is more specific to rc cars actually but this off shore forum is the most knowledgeable group I have found on brushless motors.

Nic Case has the wheel driven record at 202 mph. He ran a 1530 motor on 12s (modified Castle hydra 240hv) supposedly with a 1875kv wind...

Another car of his was 4s running near 150mph and was running near 7000kv Neu 14 series motor in this one. It seemed to me that he had success with higher than normal KV motors.

Ultimately I'm looking at volts and amps to = watts
Mr. Case's runs were around 10 years ago. Brushless motors have not changed a lot (except TP has made more options at great prices) but LiPos and ESCs have improved some.

I am going with a catamaran design which should cut the aerodynamic frontal area nearly in half. Also the center section is an airfoil creating the needed downforce in ground effect (thanks Collin Chapman 68-79 Lotus F1). This is where I hope to make the most significant improvements over others attempts at the record.

I appreciate everyone's input!

-Liberty

[Fluid]

I met Nic at the LA SAWs around 2008. So much has changed since then it is difficult to extrapolate to modern components. I held a number of catamaran records, may still hold one, but it is not the fastest hull type. Downforce is drag, so limiting the amount of downforce is important - use just what is required, which is close to neutral. Colin was interested in using downforce to increase cornering speed rather than top speed, just like modern F1 cars.

Boats are not cars and their speed/power ratios are different - and what is best for boats may not be best for cars. But I wish you the best and you can get good help here.

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[Speed3]

12s on a 1530 can neu 1875kv. That's alot of power. You made mention that the record was done 10 years ago.

The good news is the cells today are more potent so if you ran the exact setup as him, using some of the best cells today you probably would be a little faster.

I can tell you the more cells you use the more power you would have. I don't think you stand a chance at his record on 8s.

If you take 2 motors same can size, (1 being a 4074 2000kv on 4s and 2 behind a 4074 1000kv on 8s)
Rule of thumb motor 2 should be produce a little more power. Lower kV in my experience is a little more efficient.

To make it clear if you are restricted to a certain cell count the higher kV should win. And they is nothing you can do with the lower kV to beat the higher kV on an equal cell count.

It have 16s capable ESC, one of those with a 16s setup can offer more power than the 12s setup you want to beat.

If it is possible to use 2 motors the 2 would split the load and be more powerful than one.

But take this concept if it is a car you are building, visualize loaded rpm, its necessary to selecting the right gear ratio, and tire diameter has to be factored in the equation. Tire diameter because you can use the pie*diameter equation to calculate distance travelled per rotation.

The idea is to theoretically build for a certain speed in distance per second.( using a theoretical loaded rpm, tire circumference and gear ratio)

The more cells the more power available and higher rpm potential.

I would use twin tp 4070 if possible as the first option.

Tire diameter I think is important to for traction purposes. And it gets interesting in that with all this power, can drive assembly handle all this torque.

[LibertyMKiii]

I agree a 4070 is a good place to start. Many guys are using them to get in the 150-170 range.

To clarify catamaran design on a 4 wheel vehicle this is what I am referencing:


I like the idea of a 14 or 16 cell ESC. Is MGM or swordfish my best two options?

With a long wheelbase chassis for high speed stability there will be plenty of space for battery packs.

I have a good calculator for rpms, wheel speed, distance covered, etc.

Historically tires blow up at high rpms. I spoke with John at BSR who made Nic Case's tires. He is always interested in this type of project (very nice guy).

-Liberty

[Speed3]

I have heard good about those two ESC brands. I am not familiar the higher voltage ESC first hand so hopeful someone else can guide you on those esc's.

[fweasel]

In my experience, the MGM ESC's have a significant amount of headroom above the rated current spec

[RaceMechaniX]

Are you trying to do RC car land speed or boat SAW? Boats and cars are completely different on how you select a motor.
Nic Case used a very high KV, one I would never recommend for a boat.

[srislash]

I have heard good about those two ESC brands. I am not familiar the higher voltage ESC first hand so hopeful someone else can guide you on those esc's.

Flier has esc’s Up to 24s and 400 amps, might even be a 800 on the site.

https://www.aliexpress.com/store/513485

[LibertyMKiii]

Flier has esc’s Up to 24s and 400 amps, might even be a 800 on the site.

https://www.aliexpress.com/store/513485

Don't these have a reputation for catching fire? I have seen their alien power series catch fire 1 out of 3 runs. I like the ZTW 14s 300a. This would put me in the 13-18kW range that I'm looking at.

I have the castle XL-X currently and unlocked on v1.78 can exceed 400 amps, but they also dont last long at that level.

If there were no challenges then everyone would do it...

[RaceMechaniX]

The Flier's are not great, but I have burned up plenty of Castle's and every other good ESC with the exception of the MGM's which are pretty solid at protecting themselves.
I would be impressed if you can run drive any car at 400A for more than 5 seconds without loosing control. The Castle XL-X with added caps is probably your best option of you want datalogging.
The ZTW 300A beast pro is another option. http://www.ztwshop.com/product/ztw-b...A-Car-ESC.html

Nic went 200mph with a Castle with either a castle 180HV or an ICE160HV.

If you were running an LMT motor, I would tell you to buy a Schulze 40.333 like this one. https://www.facebook.com/marketplace...4255546500984/

[LibertyMKiii]

The Flier's are not great, but I have burned up plenty of Castle's and every other good ESC with the exception of the MGM's which are pretty solid at protecting themselves.
I would be impressed if you can run drive any car at 400A for more than 5 seconds without loosing control. The Castle XL-X with added caps is probably your best option of you want datalogging.
The ZTW 300A beast pro is another option. http://www.ztwshop.com/product/ztw-b...A-Car-ESC.html

Nic went 200mph with a Castle with either a castle 180HV or an ICE160HV.

If you were running an LMT motor, I would tell you to buy a Schulze 40.333 like this one. https://www.facebook.com/marketplace...4255546500984/

The XL-X with a homemade low esr cap pack is what I run now. I do really like the data logs and their throttle curve adjustments are vital for keeping traction. My Futaba radio can do some throttle expo tuning, but the control works much better from the ESC side.
I'm not fully convinced the LMT motors are worth the cost over something like TP Power. There are plenty of people going very fast on TP motors. I just sold my TP 5870 3y to a member here, since i'll be trying a 4070 instead.

Has anyone torn down the 4070 and 4070CM to compare? Is the only difference bearings, kevlar wrap, and winding options?