T-Rex 450 3S motor mini test
Written by Ashley Davis Sunday, 09 August 2009 21:29
Motor TestIntroduction
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. All using a standard 2100mah 3S pack.
There are three new motors in this test:
JustGoFly 500TH
Spiral 2838-3900
Align 430XL
The control motor for backwards compatibility to previous tests is the Medusa 28-40-3400.
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.
| Motor | kv | Supplier | Pinion | Shaft size |
|---|---|---|---|---|
| Align 430XL |
3700
|
13T
|
3.17mm
|
|
| JustGoFly 500TH |
3380
|
14T
|
3.17mm
|
|
| Medusa 28-40-3400 |
3400
|
13T
|
3.17mm
|
|
| Spiral Technology 2898-3900 |
3900
|
11T
|
3.17mm
|
The lithium polymer pack used throughout this test was a Revolution Cellpro 3S 2100mAh 18C. This pack was used with a FMA Cellpro 4S charger. This pack was specifically selected because of its excellent thermal capabilities & good voltage hold. 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 Eagle Tree MicroPower E-Logger fitted with a brushless RPM sensor.
The test machine was a T-Rex SE V2 as standard with no upgrades.
My thanks to Aurrora for the supply of the Revolution Pack & Cellpro 4S Charger.
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 3200 rpm unloaded. The initial spool up is one minute operating at 3000 rpm+ with hovering 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 hovering 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.
| Phase | Activity | Duration | Start Time on Graphs | End Time on Graphs |
|---|---|---|---|---|
| Phase 1 | Spool Up to 3200 RPM at hovering pitch | 1 minute | 0 minutes | 1 minute |
| Phase 2 | 11° positive pitch | 20 seconds | 1 minute | 1 minute 20 seconds |
| Phase 3 | Hovering pitch | 10 seconds | 1 minute 20 seconds | 1 minute 30 seconds |
| Phase 4 | Pitch pumping | 30 seconds | 1 minute 30 seconds | 2 minutes |
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.
The Charts
The following is an explanation of the charts used to differentiate the performance of the various motors. I will use the charts generated by the 430XL motor to explain how to interpret the charts.
Below is the combined chart for the Align 430XL.
Green line = RPM
Blue line = Pack volts
Purple line = Amps
The numbers along the bottom denote minutes, each test starts some time after I plugged in the Eagle Tree logger so the minutes show from when the pack was plugged in rather than from when the test started.
The left vertical axis is amps and volts.
The right vertical axis is RPM.
The chart shows hovering up until 1.8 minutes when full pitch was applied. Then follows a peak in amps and a dip in RPM for 20 seconds to 2.1 minutes. Following this the pitch is reduced to hovering pitch for 10 seconds and a recovery can be seen in RPM and the amps required fall until just under 2.3 minutes. Lastly pitch pumping with lots of fluctuation in amps and RPM from 2.3 minutes through to 2.8 minutes.
Along the bottom of the chart are minimum and maximum values for amps, volts and RPM as well as a test average figure for each.
The following chart is from exactly the same test as the above but this time showing the amps during the test. This chart shows a steady 19A for the one-minute hovering pitch. Following this the 11° of pitch is introduced and the amps climb to almost 38A and then decay as both the pack and motor start to strain. A drop in amps is then seen during the 10 seconds that the motor is at hovering pitch. Following this we can see fluctuations in amps during the pitch pumping from approx 25A minimum to 35A maximum.
The following chart is from exactly the same test as the above but this time showing the RPM during the test. This chart shows a steady decline in RPM for the one-minute hovering pitch to approx 3150 RPM. Following this the 11° of pitch is introduced and the RPM drops steadily to almost 2400RPM as both the pack and motor start to strain. A recovery in RPM is then seen during the 10 seconds that the motor is at hovering pitch. Following this we can see fluctuations in RPM during the pitch pumping from approx 2600RPM minimum to 2850 maximum.
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 will do this comparison later in the test.
The following charts show individually each motor, what's important from these graphs is the average amps for the test as this gives an indication of which motor has the lowest amp draw and therefore the longest flight time:
Picking out the amp draw figures gives the following:
| Motor | Max Amps | Average Amps | Minimum Amps |
|---|---|---|---|
| Align 430XL | 37.63 | 25.17 | 18.81 |
| JustGoFly 500TH | 36.63 | 23.84 | 16.38 |
| Medusa 28-40-3400 | 39.5 | 26.72 | 20.28 |
| Spiral Technology 2898-3900 | 38.17 | 26.34 | 19.81 |
Working off the overall averages we get the following order for amp draw:
| Position | Motor |
|---|---|
| 1st | JustGoFly 500TH |
| 2nd | Align 430XL |
| 3rd | Spiral Technology 2898-3900 |
| 4th | Medusa 28-40-3400 |
RPM Held
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)
Here are the four RPM graphs for each individual motor:
| Motor | RPM Held |
|---|---|
| Align 430XL | 2434.06 |
| JustGoFly 500TH | 2394.12 |
| Medusa 28-40-3400 | 2509.27 |
| Spiral Technology 2898-3900 | 2429.35 |
Working off the minimum RPM held we get the following order:
| Position | Motor |
|---|---|
| 1st | Medusa 28-40-3400 |
| 2nd | Align 430XL |
| 3rd | Spiral Technology 2898-3900 |
| 4th | JustGoFly 500TH |
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.
| Motor | Min RPM | Max RPM | RPM Fluctuation |
|---|---|---|---|
| Align 430XL |
2578
|
2869
|
291
|
| JustGoFly 500TH |
2523
|
2846
|
323
|
| Spiral Technology 2838-3900 |
2595
|
2926
|
331
|
| Medusa 28-40-3400 |
2631
|
2927
|
296
|
Working off the overall RPM held in the pitch pumping we get the following order:
| Position | Motor |
|---|---|
| 1st | Medusa 28-40-3400 |
| 2nd | Spiral Technology 2898-3900 |
| 3rd | Align 430XL |
| 4th | JustGoFly 500TH |
Before moving onto the next section of the test here is a summary table showing the tabular data for each motor.
| Motor |
Initial RPM
|
Hovering Pitch Amps
|
Max Pitch Amps
| Max Pitch RPM Held |
Recovered RPM
| Initial RPM Fluctuation |
Pitch Pumping Amps peak
|
Pitch Pumping Low RPM
|
Pitch Pumping High RPM
|
Pitch Pumping RPM Fluctuation
|
|---|---|---|---|---|---|---|---|---|---|---|
| Align 430XL |
3282
|
19.1
|
37.63
|
2434
|
3094
|
188
|
34.83
|
2578
|
2869
|
291
|
| JustGoFly 500TH |
3287
|
18.1
|
36.63
|
2394
|
3031
|
256
|
33.97
|
2523
|
2846
|
323
|
| Spiral Technology 2838-3900 |
3285
|
20.1
|
38.17
|
2429
|
3126
|
159
|
34.97
|
2595
|
2926
|
331
|
| Medusa 28-40-3400 |
3217
|
20.55
|
40.84
|
2509
|
3094
|
123
|
38.44
|
2631
|
2927
|
296
|
The following table summarises the test minimum, maximum and average values for amps, volts and RPM.
| Motor |
Minimum Volts
|
Maximum Volts
|
Average Volts
|
Minimum Amps
|
Maximum Amps
|
Average Amps
|
Minimum RPM
|
Maximum RPM
|
Average RPM
|
|---|---|---|---|---|---|---|---|---|---|
| Align 430XL |
9.57
|
11.48
|
10.39
|
18.81
|
37.63
|
25.31
|
2434.06
|
3282.32
|
2917.06
|
| JustGoFly 500TH |
9.7
|
11.41
|
10.56
|
16.38
|
38.63
|
23.83
|
2394.12
|
3287.68
|
2893.46
|
| Spiral Technology 2838-3900 |
9.38
|
11.08
|
10.24
|
19.81
|
38.17
|
26.34
|
2429.35
|
3285.11
|
2926.05
|
| Medusa 28-40-3400 |
9.57
|
11.15
|
10.43
|
20.28
|
40.84
|
27.41
|
2509.27
|
3217.33
|
2917.44
|
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.
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):
| Motor |
Average Amps
|
Flight time
|
|---|---|---|
| Align 430XL |
25.31
|
3mins 58secs
|
| JustGoFly 500TH |
23.83
|
4mins 13secs
|
| Spiral Technology 2838-3900 |
26.3
|
3mins 49secs
|
| Medusa 28-40-3400 |
27.41
|
3mins 40secs
|
The overall ranking on efficiency (or lowest amp draw across the test) is as follows:
| Position | Motor |
|---|---|
| 1st | JustGoFly 500TH |
| 2nd | Align 430XL |
| 3rd | Spiral Technology 2838-3900 |
| 4th | Medusa 28-40-3400 |
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.
| Motor | Weight (g) | Price ($) |
|---|---|---|
| Align 430XL |
70
|
56
|
| JustGoFly 500TH |
62
|
60
|
| Medusa 28-40-3400 |
100
|
80
|
| Spiral Technology 2838-3900 |
102
|
50
|
We can see that two motors are 100g and two are 30-40g less than this. Those two lighter motors will gain a small advantage for in flight performance due to the weight saving.
The ranking on price is as follows:
| Position | Motor |
|---|---|
| 1st | Spiral Technology 2838-3900 |
| 2nd | Align 430XL |
| 3rd | JustGoFly 500TH |
| 4th | Medusa 28-40-3400 |
The ranking on weight is as follows:
| Position | Motor |
|---|---|
| 1st | JustGoFly 500TH |
| 2nd | Align 430XL |
| 3rd | Medusa 28-40-3400 |
| 4th | Spiral Technology 2838-3900 |
Conclusion
As with all tests it eventually becomes necessary to pick the winner. Listed below are how each motor performed in each individual test:
| Motor |
Amp Draw
|
RPM Held
|
Pitch Pumping
|
Efficiency
|
Weight
|
Price
|
|---|---|---|---|---|---|---|
| Align 430XL |
2nd
|
2nd
|
3rd
|
2nd
|
2nd
|
2nd
|
| JustGoFly 500TH |
1st
|
4th
|
4th
|
1st
|
1st
|
3rd
|
| Spiral Technology 2838-3900 |
3rd
|
3rd
|
2nd
|
3rd
|
4th
|
1st
|
| Medusa 28-40-3400 |
4th
|
1st
|
1st
|
4th
|
3rd
|
4th
|
As always I pick an overall performance winner and an all round winner.
Picking the performance winner is fairly easy, the Medusa was a clear winner in this area but has the biggest amp draw and highest price. However for the 3D fliers it provides awesome performance and is still one of my favourite motors.
Picking the overall winner is a lot harder but in this test I'm going to go for the Align 430XL, it gave an excellent all round performance and placed highly in most of the tests. It's nice to see Align finally produce a highly competitive motor for the 450 class helicopter.
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.
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.
( 8 Votes )
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