Xpert SI-3401 Servo install and impressions

When it comes to servos everyone has their favorites, be it Hitec, Airtronics, Futaba, Savox, Radiopost, KO Propo, or even Ace. Well now thanks to the folks at Viper-RC, we have a new choice in the US market with Xpert-RC. Viper is now the exclusive distributor of Xpert servos in the US. New options are always exciting!

We were given a unique opportunity to try out some of these new servos. The first one we’re testing is the Xpert SI-3401 Low Voltage Brushless servo. Actually I should note that all Xpert servos to be sold by Viper will be Brushless models as they provide better power, speed and control compared to coreless designs. They also offer reduced current draw, increased efficiency and reduced running temperatures.

The Xpert SI-3401 is a low voltage (4.8V- 6.6V) servo which features a brushless motor and comes in a partial aluminum outer case. It features 4096 steps of resolution to provide extremely precise control over your steering. The SI-3401 has full ball bearings and metal gears for a precise and durable drive train.

Below are the full specs.

  • Speed: 0.08 sec/ 60 deg (at 6V)
  • Torque: 11.34 kg/cm or 157.41 oz/in (at 6V)
  • Speed: 0.1 sec/ 60 deg (at 4.8V)
  • Torque: 9.07kg/cm or 125.92 oz/in (at 4.8V)
  • Voltage Range: 4.8V- 6.6V
  • Frequency Range 50-400Hz
  • Bearing: 2BB
  • Dimensions: 40 x 20 x 37.8 mm
  • Weight: 62.5g

Without further ado, let’s jump right into the install. I’m installing this into my 2wd Associated SC10. My previous setup was a Savox SC-1258TG servo, Viper VTX10-BE, Spektrum radio, CRC lipo, Thunder Power motor and of course with the Savox servo I needed a cap (aka glitch buster) to prevent brown outs. I was running a massive Novak cap.


This is the package the SI-3401 servo comes in. It’s a decent little package that is well thought out. The servo doesn’t bounce around in shipping.



Pretty cool servo when having it out and playing with it. The fit and finish seems nice and appears to be well built. The aluminum lower case half is something a lot of servo companies are doing to help with heat dissipation. Most of the higher end (>$50) servos have this feature.


So first I’ll start by taking the old servo out. I love how on the SC10 that only means 2 screws.


Servo is out!


A side by side comparison yielded some surprising results. The Xpert servo is actually somewhat taller than my old one. I had been under the impression they were the same.


At the sight of this I was having concerns if it would actually fit in my application.


I dropped it in the truck quick for a mock-fitting and it fit, barely. One nice thing about this servo is it uses a 25T spline which is the same as Savox and Futaba. I was able to just remove my horn off the old servo and transfer to the Xpert servo. I love it when things are simple.


I then did a final install of the servo. I had to shim the servo mounts to get them to line up. The servo wouldn’t go back any further as it hits the chassis wall. This is as far back as it will go.


The photos are a little deceiving as it looks like the servo linkage and bellcrank hit the servo, but they don’t. It clears the servo case thru the range of the servo’s motion, but not by much.


Below is a video of the servo in action after just installing it. You can see it has full motion. It’s actually quite fast and responsive as well.


So, how did it perform you ask? Well, I thought it did quite well. One immediate observation was how quiet this servo is compared to what I was using. For instance when it’s on and in resting position it doesn’t have that incredibly annoying buzzing whine of the Savox servos. Being brushless and therefore more efficient, I was also able to run without the huge glitch buster I had installed.

As far as on-track performance, I used this servo exclusively last weekend at Motorama. I installed it when first arriving and it didn’t miss a beat all weekend. My truck was as predictable and easy to steer as it ever was with the old servo. I thought it performed great. Less noise plus no glitch buster are a win in my book.

In my opinion, one race isn’t enough to truly judge a product, even one as long as Motorama. My first impressions are positive though, and look for a long term review later.

Xpert servos will be available via from Viper R/C Solutions retail and distribution partners or directly from www.shopviperrc.com. With dedicated customer and warranty support available via Xpert-RC USA. Check out www.xpert-rc-us.com for more information.

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