Power delivery from a brushless motor largely depends on the operating temperature throughout the duty cycle, this includes both the stator, magnets and windings. While initial power may be high a motor can quickly heat soak causing the available power to rapidly reduce well below the potential of Individual components mainly the magnets and windings.
KO has identified this as the main limiting factor when developing a motor to meet the high demands placed on a multi rotor motor. Our solution has been to completely redesign the fundamental components and the way they interact.
Firstly the ACPC ring design on all of the KO motor offerings, this allows for maximum air flow through the stator and magnet assembly without robbing the motor of power to drive a fan style system however this is only the first step . The next step is where Cryo comes into play . Cryo spray is a specially formulated freezing agent designed to drop the standing temp of the stator, windings and magnets to -30°c ( depending on ambient temp ) in order to both increase power as well as lengthen the operational envelope the motors can deliver peak power before heat soak causes power loss.
This sounds simple in theory however many hurdles had to be overcome to allow the motors individual parts to cope with the high variances in operating temperature from -30°to +30 °c or higher. To achieve this many problems had to be overcome , testing showed stators will de-laminate after several uses due to the drastic temperature changes because each stator lamination will shrink and expand at a different rate causing failure , and aluminium parts would shrink at a different rate to metal parts when the Cryo spray was applied causing failure of the entire structure after very short use.
We also had failure of the adhesive used to attach the magnets to the bell etc and as if that was not enough, the effect of using a freezing agent on the stator causes a high degree of condensation ( moisture ) to accumulate resulting in rust to form very quickly after an initial application especially in humid conditions. Lastly and possibly the most challenging problem we faced is press fitted components such as the shaft, the shaft in smaller motors relies on a very tight press fit to ensure concentric mating of the shaft and bell to eliminate any vibrations.
Here is how we overcame these limitations and produced a motor capable of taking full advantage of this new tech .
Firstly the stator de-laminating - we sourced a stator coating normally used in the automobile industry. This coating allows the stator to uniformly shrink and expand under the extreme temperature variance from -30°c to +30°c or higher. This coating has also eliminated the potential for the stator to rust due to the build of of moisture caused by condensation.
Next we sourced an adhesive also from the automotive industry for the magnets and bell assembly with a temperature spread of -65°c to +265°C. This adhesive has also been used when assembling the press fitted components such as the shaft ensuring no slipping or movement when subjected to the extreme changes in temperature.
What can you expect to gain ? Bench and flight tests have shown between 10% and 15% increase in power over a non Cryo sprayed motor however that is only half the data . The real advantage is how long the motor can produce that peak power number.
Typically a motor with about 1800g of thrust will drop to 1700g within 5 seconds on a bench test and sub 1600g within 20seconds at WOT if it makes it thst far without heat soaking and completely failing due to burnt windings.
When Cryo is used this is not the case, the power figure at 20 seconds is almost identical as in the first 5 seconds and depending on ambient temperature the motor delivers close to peak power for 40- 50 seconds (before heat soak begins and the heat soak effect starts to take take place). In a non static "in flight" test the effect last linger again before heat soak becomes a factor.
This all adds up to around 1 minute of higher performance at which time the motor is at ambient temperature and a further minute before the motor is at the same operating temperature realised by a motor subjected to the same duty cycle without Cryo. This is 2 minutes of flight with a higher power , so essentially an entire flight depending on battery size.
The second advantage is efficiency ! By lowering the temperature of the stator and windings internal resistance is close to half that of the same windings at ambient temp of +30°C meaning not only do you get more power you also use less battery to achieve that power giving longer run times and less amp draw over that first 40 - 60 seconds of flight.
As a side bonus every time you spray the motor with Cryo spray you are also Cryogenically tempering the aluminium , titanium and steel components of the motor. Cryogenic tempering is used on many products such as drill bits and hardened tools etc , while this is generally done at sub -200°c to achieve total effect is is true that every degree achieved below 0°c will have some effect in this area by further aligning the grain structure within the metals making them stronger and more robust.
Can you use the Cryo spray with other brands ? The short answer is yes but this comes with a disclaimer .. In tests we have conducted with other motor brands there is a high failure rate in metal components , magnet slip , windings and stator de-lamination, so use at your own risk with other brands not specifically manufactured to work with Cryo.
Common failure are the windings, as most if not all popular motors on the market are machine wound and this cause small scratches on the enamel coating when passed at high speed through the guides of the winding machine.
When Cryo is added to these scratches the damaged enamel shrinks and flakes off of the windings and a dead short in the system soon follows. We hand wind each and every motor to ensure this is not a problem. Second is magnet slip . Every non KO motor tested with Cryo had magnet slip at some stage due to the adhesive used not having the required operating temps and failing as a result of the dramatic changes in operating temps.
Next was stator de-lamination caused by individual stator laminations shrinking and expanding at different rates, eventually causing layers to move pinching motor windings, causing a dead short and a burnt motor winding .
Lastly rust on the stator. Every motor tested without the KO Cryo stator coating formed rust within 48 hours of initial application regarles of humidity. So while Cryo spray will work on your motor we can not guarantee how long your motor will last or if failure will occur in flight causing damage to other components, so please be careful when deciding to use Cryo on other brand motors not employing the full spectrum of KO Cryo tech.
How do I use KO Cryo ? Very simple ! Point the nozzle into the opening at the top of the bell between the motor spokes and give a 5 second burst of Cryo spray .. For ultimate effect give a 5-6 second spray into the windings and allow the stator , windings and magnets to cool before giving a second 5 second burst of cold spray into the windings / stator followed by a 3 second burst on the outside of the can where the magnets are located .
You can also spray up into the windings at the base of the motor for a few seconds, as well as your motor wires as this will all help reduce resistance within the power train. However be careful not to spray directly onto your esc if using arm mounted ESCs.
Cryo spray is non toxic however we do recommend caution is taken to not spray the skin , eyes or any exposed parts of the body due to the extremely low temperature the spray can achieve in very little time.
Lastly if you are using one of the Method range of motors then you have another level ! The KO RaceoilX product used with the Method range of motors is rated to -65°c ! To fully realise the potential of RaceoilX and Cryo simply fill the sump with enough oil to coat the bearings and shaft and no more.. Then remove the sump plug , insert the Cryo nozzle into the sump and give a 5-10 second burst of Cryo spray. This will freeze the motor from the inside out giving an even greater cooling effect while the KO Race oil X will stop the bearings from freezing together and eliminate any chance the bearings will rust due to the moisture from condensation. Happy flying.
The KO team