Review: Castle Creations Quadpack 25 ESC

by Oscar

How about some ESC that isn’t BLHeli or KISS? Castle Creations developed the Quadpack ESC’s for multirotors that use their own custom firmware, with some very interesting features.

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The Quadpack 25 ESC’s are available at Castle Creations. They have been making ESC and motors for RC cars, planes and Helicopters for a long time, and they have now started making ESC for multirotors as well.

In the Quadpack 25, one ESC comes with BEC and the other 3 don’t. But you can also buy them individually on their store.

Castle Creations Quadpack 25 ESC package

Specification of Quadpack 25

  • Supports 2S-6S LiPo
  • Current: 25A Continuous, 45A with good air flow (40mph)
  • Weight without wires: 6.5g (No Bec) 6.7 (with BEC)
  • Weight with wires: 18.9g (No BEC) 19.1g (with BEC)
  • Dimension: 18.2mm x 43.7mm x 8.1mm
  • BEC: 5.5V @ 3A (8A peak)
  • Processor: Silabs F802 (25A version), Silabs F541 (35A version)

Castle Creations Quadpack 25 ESC wires cables


It’s worth mentioning that the BEC outputs 5.5V not 5V. I am still a bit concerned although Castle Creations reassured me that most 5V devices have some degree of tolerance, and 5.5V should be safe. The 5.5V was chosen because it’s better for vehicles running servos off of the BEC rail. I am confused why they would design an ESC for multirotors and keep thinking about supporting servos. Maybe for tricopters, but I have seen 5V runs just fine on them.

Non-BEC version – need separate power (What?!)

I was surprised in a bad way when I found out that the non-BEC ESC requires separate power source while they are connected to LiPo. Which means you need to feed the ESC 4.5-8V through the servo lead to run them, that’s reason why they have provided an ESC that comes with BEC. Low voltage circuit is separated from high voltage circuit, probably to keep out the noise? But since we have been fine combining them in majority of the ESC we use maybe this is not needed after all. Besides more and more FC start to get rid of the 5V rail in the ESC signals, this might become a problem these ESC in the future.


The wires that have been soldered on the ESC are heavy. Those are 16AWG silicon wires, they chose thicker wires to reduce resistance in the multirotor. They explained it’s a trade off between weight and resistance.

But I really think that’s unnecessary given that most of the mini quad motors I have seen use 18AWG wires. Also, many users prefer to solder the motors on the ESCs directly to keep wires as short as possible anyway.

If you decide to de-solder those ESC wires, pay extra care as there are some tiny SMD components right next to the solder joints.

Castle Creations Quadpack 25 ESC bus bars smd components

Bus Bars

The metal bars on the ESC PCB are bus-bars. They are made of pure copper and they are used to reduce the circuit board resistance. Resistance is one of the primary losses of efficiency (and causes of heat) in an ESC. Bus-bars have a dramatic effect on controller performance.

Castle Creations Quadpack 25 ESC BEC ferrite ring input power capacitor

Electrolytic Capacitor

There is a 220uF electrolytic capacitor at the Input, to reduce voltage spikes created by the ESC. But having a large capacitor hanging around, it’s possible that it gets beaten up and fall out in crashes (happens many times to me with the Blue Series ESC). The latest ESCs normally use SMD capacitors to prevent this from happening. They explained:

In the past we have done a lot of experimenting with using ceramic SMD input capacitors. The problem with ceramic capacitors is that their ESR (Equivalent Series Resistance) is too low for this application.

Almost all ESCs could use more capacitance than is feasible to put in applications with limited space and weight. With the lower ESR of ceramics the capacitors can cause input voltage ringing that is worse than if no capacitance was used at all.  We have seen and measured this on some competitive products. We are still looking for a better solution but for right now electrolytic capacitors are the best solution we have found.

On the BEC version ESC, there is also an additional ferrite ring on the signal servo wire.

Here are some close-up pictures of the PCB after I removed the heatshrink and heatsink.

Castle Creations Quadpack 25 ESC PCB front Castle Creations Quadpack 25 ESC PCB back

What’s special about the Firmware?

Castle Creations explained how their custom firmware is different compared to BLHeli and KISS:

Our firmware is one of the big things that has set us apart from the competition in other RC hobby markets.

With our latest firmware release we believe that we have made some significant improvements over both the BLHeli and KISS firmware. I think the feature that will make the biggest difference is our new Adaptive Timing System.

We are using some custom hardware to monitor the motor and automatically adjust motor timing for peak performance. This leads to longer flight times, faster motor response, and more thrust overall. We have seen some very impressive test numbers and the difference is pretty noticeable in flight. We have also done a lot of work to make the throttle response very linear. This makes the motor behave more predictably and in my experience has made my quads easier to tune and more stable in flight.

No Hardware PWM

Hardware PWM has been proven to work well and it’s a big contributor to the smoothness of KISS and BLHeli_S ESC. Castle Creations’s Quadpack doesn’t use hardware PWM but software generated. I was going to put that as a “Con”, but I am not certain just yet as they explained:

The PWM signal is generated in software. We are using a unique PWM scheme that is quite a bit more complicated than standard PWM. Our PWM scheme was implemented to increase the controller efficiency, input to RPM linearity, and motor tracking.

There is quite a bit of communication between the PWM generation routines and the motor tracking routines that wouldn’t be possible using the processor’s PWM hardware. Our software PWM scheme is structured in a way that keeps the throttle resolution just as high as you would get with hardware PWM. We have seen very good results from this algorithm in the lab.

I guess I can only find out if this is actually as good as Hardware PWM when I fly them.

Support for Oneshot42 and Multishot?

I noticed the Quadpack ESC’s currently only support Oneshot125, but not the newer Oneshot42 and Multishot. So I asked if they have any plan to support these ESC protocol in the future:

We are considering it. Both are possible and Oneshot42 is likely in the future. We have done a number of things to improve the throttle smoothness on our controllers that we believe solves some of the same problems that Oneshot42 and Multishot were trying to solve.

ESC Programming / Flashing

To flash the Quadpack ESC, a programming adapter is required. Connect the adapter into your computer with a mini USB cable, plug the ESC servo lead into the adapter, the software will automatically establish connection with the ESC.

Castle Creations Quadpack 25 ESC programming adapter

The software interface (Castle Link Download) is very user friendly to use. There are only 3 tabs, and gives you the option to set end points, change rotation direction, enabling Active Braking and updating firmware.

Castle Creations Quadpack 25 ESC software interface

They are also consider to add support for FC passthrough in the future, which is similar to how BLHeli does it.

Bench Test

Before the test, I upgraded to the latest firmware V5.00 beta, apparently this gives much more power and thrust. It also added support for active braking in the latest version.

DYS SE2205 2300KV

Tested Propellers:

  • Gemfan 5030
  • DAL 5040×3
  • Kingkong 6040



EMAX RS2205 2300KV

Tested Propellers:

  • Gemfan 5030
  • DAL 5040×3



So purely looking at the data, the Castle’s quadpack seems to perform pretty well, especially when it was with the RS2205 motors, the thrust numbers are very impressive.

During the test, I noticed the Quadpack ESC’s didn’t sound as “smooth” as the BLHeli_S nor KISS ESC. It sounds nosier than the other too especially at lower throttle. Quoting James, Software Developer at Castle Creation’s comment about this noise:

I believe you are talking about the static/hissing noise. This is an artefact of our PWM technique. It was implemented to increase throttle linearity which translates to more stability and easier PID tuning.

I personally like the noise because it gives my quad a unique sound, but I can understand that not everyone will feel that way. The ESC is running smoothly, it just sounds a bit different. In our testing we have seen that plots of input signal to output RPM are more linear for our ESCs than the competition.

Braking is great, however there are 2 separate braking settings: Active Braking and Idle Braking. I thought the maximum Idle braking value was 75% and I didn’t realize there is also a “Custom value” where I can set it to 100%. So in the video you are seeing the 75% idle braking power when I cut throttle. I can’t redo this test yet as I currently don’t have the time. But braking above zero throttle is excellent as you can see in the video.



  • Offer BEC and no-BEC versions
  • The BEC is rated at 3A which is pretty powerful
  • ESC stays cool on bench test, while the Aikon and KISS ESCs got noticeably hotter
  • Seems to deliver similar amount of thrust if not more, compared to Aikon SEFM 30A (BLHeli_S) and KiSS 24A ESC


  • Only support Standard PWM and Oneshot125, but not Oneshot42 and Multishot
  • ESC programming requires adapter, cannot be configured/flashed via FC like BLHeli
  • Has a huge capacitor
  • heavy – even heatshrink weights nearly a gram
  • BEC output 5.5V, some device might not like
  • Non-BEC version ESC must be powered by separate power source, as well as connecting to LiPo battery
  • Doesn’t sound as “smooth” as BLHeli_S and KISS

The ESC isn’t designed the way I would have expected for the use of a mini quad, the Quadpack ESC does deliver some impressive numbers from my bench test. It would be interesting to see how they perform in the air and what products they can come up with in the future.

The special technique they used to generated PWM signal isn’t being considered yet in the Pros and Cons. I will come back and update once I have tried them on a quad.

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D-on 5th September 2016 - 6:08 am

The electrolytic cap is good quality though. I wonder why though they haven’t mentioned tantalum polymer, they are quite expensive but shouldn’t have issues like a ceramic while still being SMD and don’t suffer from violent flaming failure like wet tantalum.

Tim 31st August 2016 - 12:28 pm

In response to the price, keep in mind Castle products are made in the USA, by folks earning a living wage. All the design and software development is done in-house too. I’ve been in RC since the early 90’s, and I bought my first Castle product in 1998. They are behind the curve in multirotor products, but I’m pretty impressed with how the V5 Quadpack software does in flight on a 250 racer. I look forward to Oscar’s in-flight review

Chris Barth 21st August 2016 - 1:49 am

The reason they use a 5.5V BEC is because these ESC’s are direct descendants of the original Phoenix ESC line Castle had for Planes/Helis. The planes/helis needed 5.5V to power their servos, the .5V boost in voltage helps with voltage drop with high loads and makes the servos a little faster. It a pretty old design, more than 10yrs old, they may have redesigned some of it but last I read is that they are Phoenix ESC’s one with the BEC, and three without. Still, they seem to work well from what some people say but Ive only seen them used on larger 450 size and up quads.

Chris Barth 20th August 2016 - 11:45 pm

I’ve used a lot of Castle ESC’s beginning when I started electric flight in 2003. For planes and Heli’s they were/are the cream of the crop. Very expensive though, I shudder to think of the money I have spent for them in the past.
When I built my first quad I had to build the FC myself from an Arduino and Nintendo Wii controller parts to use Multiwii firmware, premade hardware wasnt around yet. For ESC’s, I naturally looked to Castle, I bought four Phoenix 45 ESCs for about $90 each! Yes, $90 EACH!!! I got everything put together and flew it, it flew but flew like crap. I used Castle link and tried the firmware they had for multicopters but it still flew terrible. Then I read about using cheap hobbyking ESC’s and flashing them. I bought some blue series 30A and put SimonK on them. The difference was night and day with the cheap ESC’s! I couldn’t believe that a $15 ESC could outperform a $90 ESC but it did, and it did it reliably.

Castle is a little late to the game with their quad ESC’s. I’m not sure how many people will buy these when they can buy something like four 30A Cicada/Racerstars(excellent ESC BTW!) for third of the price. IMO Castle missed the boat, make that a supertanker! I really think that they thought their products were superior and no one would rely on cheap reflashed ESC’s from Hobbyking to be on their multicopter.

Oscar 22nd August 2016 - 3:18 pm

indeed, when i first got their ESC i thought they are about 12 months behind the current hobby (maybe longer). I wasn’t aware their history and how long they have been in RC industry, as multirotor is the only thing i know in RC lol :D

George 18th August 2016 - 2:02 pm

You forgot one big con, PRICE!

Oscar 22nd August 2016 - 2:58 pm

true that!

MikeF 18th August 2016 - 1:36 am

I feel like I just slipped back 5 years.
Castle has probably been so focused on cars and planes that they weren’t really paying attention to what’s been going on with racing quad technology like ESCs, motors, flight controllers. If we have BLHeli, BLHeli_S and KISS to choose from, Castle would need to come up with something significantly better to get people to switch. An important point to remember is that thrust isn’t everything. I heard that from the KISS people many times.

Mootronic 19th August 2016 - 11:39 am

Totally agree with you.

They would better have to make one ESC with 5V BEC, an other one with 12V BEC, and the two others with they own BEC for internal circuitry. In this way: no need of PDB :)

Mootronic 19th August 2016 - 11:39 am

PDB, with BEC, obviously -_-