Futaba 3154 micro digital servo
| Reviewer | Ashley Davis |
|---|---|
| Review Date | 26th April 2007 |
| Supplier | TrexTuning |
| Model | Futaba 3154 |
| Unit Cost | £24.99 |
Box
Bendy Servo horn 
Front view 
Compared to a UK penny
Overview
4.8V |
6V |
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| Speed | 0.10 / 60° |
0.09 / 60° |
| Torque | 20.8 oz-in |
23.5 oz-in |
| Size / Weight | 0.86 x 0.43 x 0.78 inches / 0.27 oz |
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This is a new servo from Futaba which based on its statistics looks to be designed for the T-Rex as a tail servo. This is a true micro servo rather than the mini servos typically used on the T-Rex as a tail servo (e.g. Futaba 9650). It is a very fast servo with just 0.09 seconds to travel 60° when running at 6 V.
This servo will be tested in two different environments. Firstly with the Logitech 2100 gyro running at 5 V. Secondly with the Futaba 401 gyro running in digital servo mode at 6 V.
Flight Review
I ran the servo for numerous flights on 5 V with the Logitech 2100 gyro. The model used in this instance was the Dragonus. In this configuration the gyro performed extremely well although it would allow the tail to blow out and on occasion I felt that the servo didn't have enough power to handle the tail. The other disconcerting factor with regard to the servo is that the servo horn is extremely soft and bends easily. I didn't like this at all and ended up using the shortest arm I could get away with in order to avoid the servo arm bending all over the place.
The second configuration was running this servo on the new T-Rex SE V2. For this configuration I had a Futaba 401 gyro which was running in DS mode. Additionally the T-Rex SE V2 comes with a 6 V ESC and so the voltage was also higher. In this configuration I burnt out two 3154 servos in quick succession. The first one failed due to the motor burning out and locking up, this incident being the catalyst to my first pirouetting auto with the little T-Rex. The second servo failed due to a component burning out on the digital control board for the servo. Collectively both servos lasted a total of four flights on the T-Rex SE V2. I decided that 6 V and DS mode clearly weren't something that the 3154 was able to cope with.
| Pros |
|---|
| Very small and lightweight |
| Fast |
| Relatively cheap |
| Cons |
|---|
| Not enough torque |
| Servo fails in DS mode on a Futaba GY401 gyro |
| Awful bendy servo horn |
| All in all probably not suitable as a tail servo for a T-Rex |
Conclusion
I have had a very mixed experience with this particular servo. Clearly it cannot cope with a 401 gyro in DS mode. This does not mean it will not work with other less demanding gyros, when it was working in the Dragonus it did work reasonably well.
Update 13-06-2007
Following more testing the servo has been found to last ok when used in DS mode but with a 5V ESC. It appears it is 6V from the SE V2 ESC that is causing the servo failures. The way to resolve this is to put an Align 5.1V step down regulator between the 401 gyro and the S3154 gyro. Once this is done the lifetime of the servo dramatically improves and it does a pretty good job, although I still think it needs more torque.
Overall if you are running less than 6 V and are happy with the bendy servo horn then the Futaba 3154 may well suit you. For 3-D pilots who are extracting a little more from their machines and most particularly T-Rex SE V2 owners don't go anywhere near it unless you run the 5.1V step down regulator, without this it WILL fail and probably cost you a lot more than a servo in repair costs.
Update 15-06-2007
I was informed today that the Hitec HS55 servo horn is actually a perfect fit for the 3154, so this potentially solves the bendy servo arm problem. Thank you to Aurelien Doux for this tip.
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