Tenshock RC906: yes or no ?

[JatoTheRipper]

Originally Posted by JohnRobHolmes

Sooooo, you do know that motor torque is based on the motor size/design and not the Kv, right? This is an old saying from brushed motors that does not translate to brushless. While higher Kv will have more copper losses in the ESC phase side and wires between esc and motor, this only causes a bit more motor rpm increase when unloading occurs. Torque loss is only an after effect of decreased ESC efficiency, and we should actually see an increase in torque if the motor is not saturated and phase amps not limited.
If he had simply regeared the motors as should be done, the higher Kv motors would have started up BETTER and produced MORE torque at the wheel and the shaft. Volt up, gear down. Or Kv up, gear down. It works the same.

More direct to the point of high Kv motors sensorless having startup problems. The problem with high Kv motors running sensorless is not the lack of torque, it is the low inductance and low bEMF making sensorless feedback difficult if regearing is not done to increase commutation rate accordingly. The obvious culprit of his setup (besides not regearing) was the async rectification causing the diode drop to mask part of the bEMF. On a sidewinder 4 the performance differences would be more difficult to see. If he had properly regeared the higher Kv motors would have been hands down winner.


Because of gearing limitations in our rigs, there will be a threshold where Kv does impact sensorless startup because further geardown is not possible. Every setup is different, but there is absolutely no reason that a modern truck running 4.75" tires can't run a sensorless 2800kv motor on 3s effectively.

Great info!

[JohnRobHolmes]

Here is an absolutely fabulous simulator output that an engineer has developed in conjunction with his test equipment. It is by far the best simulator I have found, and is developed for ebikes but works for any permanent magnet motor system where the system constraints are known. everything is modeled, including thermal transfer over time. Find it at Ebikes.ca in the tools section if you want to play around with it.


What we are looking at is a 7 turn motor (motor A) vs a faster 5 turn motor (motor B). I have changed the constraints to have no battery or phase amp limiting to better reflect how RC car systems work, IE we are mostly constrained by system load, resistance, and inductance. As shown, the higher Kv motor produces more torque, more power, and more speed along the entire curve. Higher Kv will produce MORE torque at a certain voltage, until it reaches a saturated state, as long as the ESC is large enough to handle the current. If I "geared it down" too, it would absolutely smash the lower kv system in performance. The volt up gear down mantra I have pushed in the Ebike world as well, and it has been very well received and used.

This does not reflect the issues that higher Kv motors present to sensorless commutation, but gearing down gets around that. A 20% increase in Kv would ideally be met with a 20% increase in gear reduction so that the commutation rate was also 20% higher. Higher commutation rate gives better sensorless feedback and gets out of the "dead zone" faster all else equal.

Point being, with any sensorless system there will be a threshold of wheelspeed where low speed control becomes poor, but it is not because of torque loss. The fix is always more geardown or going sensored.

[JatoTheRipper]

Originally Posted by JohnRobHolmes

Here is an absolutely fabulous simulator output that an engineer has developed in conjunction with his test equipment. It is by far the best simulator I have found, and is developed for ebikes but works for any permanent magnet motor system where the system constraints are known. everything is modeled, including thermal transfer over time. Find it at Ebikes.ca in the tools section if you want to play around with it.


What we are looking at is a 7 turn motor (motor A) vs a faster 5 turn motor (motor B). I have changed the constraints to have no battery or phase amp limiting to better reflect how RC car systems work, IE we are mostly constrained by system load, resistance, and inductance. As shown, the higher Kv motor produces more torque, more power, and more speed along the entire curve. Higher Kv will produce MORE torque at a certain voltage, until it reaches a saturated state, as long as the ESC is large enough to handle the current. If I "geared it down" too, it would absolutely smash the lower kv system in performance. The volt up gear down mantra I have pushed in the Ebike world as well, and it has been very well received and used.

This does not reflect the issues that higher Kv motors present to sensorless commutation, but gearing down gets around that. A 20% increase in Kv would ideally be met with a 20% increase in gear reduction so that the commutation rate was also 20% higher. Higher commutation rate gives better sensorless feedback and gets out of the "dead zone" faster all else equal.

Point being, with any sensorless system there will be a threshold of wheelspeed where low speed control becomes poor, but it is not because of torque loss. The fix is always more geardown or going sensored.

I used to work next to a guy that designed custom brushless motors for extreme conditions for the military. I loved watching him design in software like this.

[baruch620]

Originally Posted by JohnRobHolmes

Here is an absolutely fabulous simulator output that an engineer has developed in conjunction with his test equipment. It is by far the best simulator I have found, and is developed for ebikes but works for any permanent magnet motor system where the system constraints are known. everything is modeled, including thermal transfer over time. Find it at Ebikes.ca in the tools section if you want to play around with it.


What we are looking at is a 7 turn motor (motor A) vs a faster 5 turn motor (motor B). I have changed the constraints to have no battery or phase amp limiting to better reflect how RC car systems work, IE we are mostly constrained by system load, resistance, and inductance. As shown, the higher Kv motor produces more torque, more power, and more speed along the entire curve. Higher Kv will produce MORE torque at a certain voltage, until it reaches a saturated state, as long as the ESC is large enough to handle the current. If I "geared it down" too, it would absolutely smash the lower kv system in performance. The volt up gear down mantra I have pushed in the Ebike world as well, and it has been very well received and used.

This does not reflect the issues that higher Kv motors present to sensorless commutation, but gearing down gets around that. A 20% increase in Kv would ideally be met with a 20% increase in gear reduction so that the commutation rate was also 20% higher. Higher commutation rate gives better sensorless feedback and gets out of the "dead zone" faster all else equal.

Point being, with any sensorless system there will be a threshold of wheelspeed where low speed control becomes poor, but it is not because of torque loss. The fix is always more geardown or going sensored.

Hello there John,
I would like to know your opinion on my future setup..
I have Axial Bomber [Kit] with SSD 2 speed gears inside...works great with 32P gears at 64/12. now it's on 3s with 21T 550 can.
I want to go with the new castle Sv4 and Tenshock 906 with 2400kv....you think it will crawl well with my setup? [crawling only on lower gear, ssd gives 2.34:1]

[JohnRobHolmes]

I don't have a bomber with the 2 speed. If your final ratio is 35:1 or more, should be fine.

[treadway47025]

What about 1750 tenshock with mamba max pro

[Voodoobrew]

Just an FYI the sidewinder 4 has the smoothest start if you choose sensor less. Better than the sw3 and mamba x.

[old man 52]

So the sidewinder 4 is the best esc over the mamba x for this motor ?

[JohnRobHolmes]

Marginally, yes. If you want more flexibility the X is still great.

[old man 52]

Thanks John, appreciate your input for sure

[old man 52]

So since we moved our home pc is toast , now i can't program a castle system , what do you guys think of the Hobbywing bl10 60 amp or the 120 and , i could use their program box to set it up , this it just going in my trail rig , any info would be appreciated ,

[old man 52]

Update , sw4 , Tenshock 1750kv in a stock TF2 , im very impressed , smooth , torque an power for days , crawling and trailing a 2200 mah last forever , looking to pickup a second ecs now

[scaled]

I have a 1250kv in a 2.2 Wraith for several years now. Nothing fancy, paired with a 120A HW ESC. Not the smoothest but durable, water resistant, and my 11 y/o out does me most days. That said I have a 2850 Slate combo, 1800 AXE (Favorite), and a SW4/1400 Revolver as well. All are very good.