3S Mini Test - 2

Introduction

There are many power systems now available for the trex which provide really excellent power and make the trex a lively and fully 3-D capable machine.

In this test I am not looking at trying to create maximum flight time. This test is looking to define which motor(s) provide the maximum power for 3-D flight with a secondary consideration to amp draw and efficiency.

There are three new motors in this test:

Scorpion HK2221-6
Scorpion HK2221-8
Genghis Titan-001

For comparative purposes I have included the following previously tested motors:

Spiral 2838-3900
Align 430XL

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Equipment

Before we move into looking at the test data I would first like to introduce the various motors that have taken part in this test. I would also like to credit the various suppliers whose motors are participating in the test. Additionally, I need to detail exactly what pack has been used in these tests and what speed controller. Following this I will explain how the test was conducted and give some explanation to the charts that have been produced.

 

The lithium polymer pack used throughout this test was a Revolution 3S 5300mAh 22C. This pack was used with a FMA Cellpro 4S charger. This pack was specifically selected to remove and pack voltage variances from the motor testing. Of course you couldn't possibly fly with this pack but it produced a good consistent voltage for the testing of the motors, which is what we are testing (not packs). The speed controller used in this test was an Align 35X 6V ESC that comes as standard with the T-Rex SE V2.

The test equipment used in this test was an Oracle datalogger fitted with a brushless RPM sensor.

The test machine was a T-Rex SE V2 as standard with no upgrades.

My thanks to Aurorra for the supply of the Revolution Pack, Cellpro 4S Charger and Oracle datalogger.

 

The Test

The motor test consists of four phases. The first phase is an initial spool up to operating RPM. I set all of the motors to run at around 3000-3200 rpm unloaded using pinions only. The initial spool up is one minute operating at 3000 rpm+ with 0 pitch on the blades. The second phase of the test is the application of 11° of positive pitch for the duration of 20 seconds. This is the main loading part of the test and is designed to ascertain what RPM the motor can hold at full pitch at the end of 20 seconds. The third phase of the test the motor is given a 10 second rest at 0 pitch. The fourth phase of the test consists of 30 seconds pitch pumping from -11° to +11°. At the end of this phase the test is complete and the motor is checked to make sure it has not hit an excessive temperature (over 80° C.). The following table summarises the test.

 

 

I should point out at this stage that none of the motors tested went over the control temperature of 80° C. Therefore I will not mention this further in the test results.

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The Charts

The following is an explanation of the charts used to differentiate the performance of the various motors. I will use the data generated by the 430XL motor to explain how to interpret the charts.

Below is the combined chart for the Align 430XL.

Green line = Volts
Blue line = Amps
Red line = Headspeed

The left vertical axis shows volts, amps and "formula 1".
Formula 1 is RPM in all cases on any of the charts in this test, it's a formula based on the actual motor RPM divided by the gearing to give the headspeed.

The chart shows spool up and 0 degrees pitch until 1 minute when full pitch was applied. Then follows a peak in amps and a dip in RPM for 20 seconds to 1 minute 20 seconds. Following this the pitch is reduced to 0 degrees pitch for 10 seconds and a recovery can be seen in RPM and the amps required fall until 1 minute 30 seconds. Lastly pitch pumping with lots of fluctuation in amps and RPM from 1 minute 30 seconds through to 2 minutes.

 

 

To ensure fair play here is the overlay of the voltage each motor was supplied during it's test. What you can see is that no motor has any significant advantage and the voltage is relatively consistent for each motor test. It's almost impossible to get it spot on as variances of a few degrees in temperature will give slightly lower or higher voltage from the pack.

You will see the Genghis appears to have a lower supply voltage than the others but actually it's down to the motor pulling more amps and causing a voltage depression. Even so it's only 0.2V or approx 50 RPM difference if you factor in the gearing.

 

 

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Amp Draw

This part of the test will focus on the amp draw of the various motors as they are put through the standard test. The amp draw consumed by the motors in isolation does not give an indication of the performance of the motor. The set of charts that follow give an indication of what sort of flight time one might expect to get on each motor. The data also shows how hard the pack will be pushed to deliver the performance. The amp draw needs to be compared to the RPM performance in order to get an indication of efficiency. I'll give approximate figures in the graph descriptions, the tabular data at the end contains the full details.

Below you can see the Genghis is pulling most amps, followed by the Scorpion HK2221-8 and HK2221-6. The Spiral and 430XL being fairly difficult to split on the overview. All the motors apart for the Genghis are fairly close in the 0 pitch section of the test but you can see them all separate in the full pitch and pitch pumping sections.

 

 

OK, so let's look closely at full pitch.

We can see the Genghis is the amp hog here managing to peak over 50A at full pitch. This is followed by the Scorpion HK 2221-8 at around 45/46A. Then comes the second of the scorpions HK2221-6 at 43/44A and finally the 430XL and Spiral difficult to separate at 41/42A. So almost ten amps difference between out most hungry motor and our most efficient ones.

 

 

 

OK, so what about the pitch pumping section. Here's the summary graph (pretty confusing eh?). We can break this down a piece at a time.

 

 

Lets take the highest amp drawing motors first.

Below we see the Genghis and HK2221-8. The Genghis clearly peaking higher than the HK2221-8. The Genghis fluctuating between 31A and 45A. The HK2221-8 is a little way behind this with fluctuations between 28A and 43A.

 

 

Following just behind the most hungry motors we have the HK2221-6 and Spiral. These two motors are very close but the HK2221-6 is the most hungry with fluctuations between 27.5A and 42.5A. The Spiral coming in behind this with fluctuations between 28A and 38A.

 

 

Lastly I've measured the Spiral up against the 430XL. With the Spiral figures at 28A and 38A we can see the 430XL manages to come in very close to this with fluctuations between 28A and 39A. Pretty much the same given the scope for error in these tests.

 

Here's the tabular data for the pitch pumping section:

 

 

Picking out the overall full test amp draw figures gives the following:

 

Working off the overall averages we get the following order for overall full test amp draw:

 

 

 

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RPM

This part of the test is looking to see how well the motor will hold a sustained heavy load. In this case plus 11° of pitch at full throttle. The expectation is that the head speed will slowly decay over the first 10 seconds or so and then the motor should hold at a specific RPM. It is the RPM at the end of the 20 seconds which differentiates one motor from another. The factors that come into play here are the heat generated whilst the motor is under load and the ability of the motor to deal with that increased heat. A good motor will hold a higher RPM and generally will generate less heat during the 20 seconds. Another important factor is how the motor recovers once you remove the load. Some motors will return to the rpm initially set, other motors will not do this. The demand placed on the pack also comes into play in this test. If the pack has been heavily loaded (beyond specification) then it may not be able to supply the required voltage immediately in order to return the motor to it's original rpm once the load is removed (i.e. once the pitch is reduced to hovering levels)

The following chart is the RPM overview. However, I also want to call attention to the chart immediately following it. The reason being that the HK2221-6 was run on a 10T pinion in this test BUT I also ran it on an 11T pinion. On the bigger pinion it's performance in terms of amp draw and RPM was as good as identical to the Ghengis. So I want to make sure the HK2221-6 gets recognised for what it can deliver when pinioned higher, all be it at a rather large amp draw premium.

So, to summarise the overview, the Ghengis and HK2221-6 (11T) are the top performers for RPM. Following this is the HK2221-8. Then following that the HK2221-6 (10T). Then comes the Spiral followed by the 430XL.

 

 

 

 

 

RPM Held

Let's take a close look at RPM held on the full pitch test.

 

 

What we see here is the Scorpion HK2221-8 holding RPM best. This is closely followed by the Ghengis and the Scorpion HK2221-6. A little way behind all the others comes the Spiral and finally the 430XL. All motors recovered RPM very well indeed after the full pitch test.

 

Working off the minimum RPM held we get the following order:

 

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Pitch Pumping

This part of the test is where the motors are pitch pumped for 30 seconds from -11° to +11°. What we are looking for in this part of the test is for a consistent RPM fluctuation across the 30 seconds. We are also looking for the smallest possible fluctuation in RPM as we want the machine to maintain as much head speed as possible. What we should not see is a slowly decaying head speed across the 30 seconds. We also do not want to see large drops in RPM. Consistency is the name of the game.

 

 

 

Working off the overall average RPM held in the pitch pumping we get the following order:

 

Before moving onto the next section of the test here is a summary table showing the tabular data for each motor.

 

The following table summarises the test minimum, maximum and average values for amps, volts and RPM.

 

 

That concludes the source data we can now use to analyse the efficiency versus performance of each motor. Based on this we should then be able to identify which motors provide the best power for the least amp draw. This is a more complicated comparison than the previous charts. However we must use the charts and this data to draw the overall winners. The tabular data shows snapshot data where as the graphs show trend data for each motor. Together these create the required information to pick overall winners.

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Efficiency Analysis

I could at this point just select the highest performing motor and ignore the amp draw characteristics. However, whilst this may be the right thing to do and fit some people's requirements it doesn't take into account all of the characteristics that a potential purchaser may be interested in. Not everybody just wants ballistic power at the expense of reduced flight time.

Personally I would want to make sure that I'm getting great performance but equally maximising my flight time as well as taking care of my pack. This is where it is worth taking a couple of moments to talk about the amp draw from these motors.

The test is conducted with the helicopter strapped down. This means that during the test the blades have to move static air. The motor is having to work significantly harder than if the model was moving through the air. This effectively pushes up the amp draw requirements during the test. In flight all of these motors will pull less amps, suffer from less head speed drop and generally perform better. We need to keep this in mind when looking at the figures and assessing whether the motor in question is suitable for our requirements. This needs to be especially considered in relation to the flight time figures in the table below as in free flight the flight time would be longer.

The table below gives an average flight time based on the test average amp draw figures utilising a 2100mah pack. This may seem unrealistic to a real flight based on the way the test is conducted but it helps put into perspective what difference the amp draw makes. The flight time is calculated using only 80% of the packs available capacity (1680mah):

 

The overall ranking on efficiency (or lowest amp draw across the test, this is not a motor electrical efficiency test which is something entirely different) is as follows:

 

 

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Weight & Price

The last consideration with regard to performance is the weight of the motor. In this section I will also include an indicative price for each of the motors. Although price has little to do with performance it is a selection criteria when choosing a new motor. The following table summarises the weight and price of the various motors on this test.

 

 

 

The ranking on price is as follows:

 

The ranking on weight is as follows:

 

 

Conclusion

As with all tests it eventually becomes necessary to pick the winner. Listed below are how each motor performed in each individual test:

 

 

As always I pick an overall performance winner and an all round winner.

Picking the performance winner

The performance winners are the Ghengis and the HK2221-6 (when using a 12T pinion, rather than the 11T used for most of this test). As I mentioned early in the test these two motors are identical in performance and therefore take joint 1st as the performance motors. However, you better have the best pack on the planet to use these as the amp draw is astronomical. The runner up being the scorpion HK2221-8.

Picking the overall winner

The overall winner is the HK2221-6 (on 11T pinion) as it strikes the best balance here between power and efficiency. Runner up is the HK2221-8 which provides great performance but at a bit of an amp draw premium. All the other motors polarise into either being efficient but not that powerful (comparatively)or very powerful but not efficient (comparatively).

It's interesting to note that compared to previous tests the new motors are more powerful but as always you never get something for nothing and more power means more amp draw. Fortunately for all of us lipos are increasing in power as well and we can therefore not all end up with puffed packs.

As a foot note it's all to easy to get overly drawn into these test facts/figures but I would like to point out that any of these motors can produce sparkling 3D performance and none of them were disappointing to fly. The data is provided to allow an informed choice. I will at a later date present some inflight data on these motors but it will need to wait for some fairer weather.

Lastly, my thanks to all the suppliers who made this test possible by providing not only motors but lithium packs, test equipment and their expertise in helping me get the best out of their motors.