When you’re looking to buy a servo, you can quite easily get lost in choosing the right one. There are so many choices available on the market. It’s worth investing in a high quality servo that will last you a long time.
On this page I am going to outline and explain, the different features of a servo. In short my recommendation is a servo which has both high torque and quick response time. For 1/8th scale you want at least 280 oz-in of torque and a speed of 0.19 sec @ 60 degree. I have been using the Hitec HS-7950TH for the past 8 years for both steering and throttle. On all of my rc cars on road and off road.
What is the speed?
The speed rating on a servo is usually less than 3 tenths of a second. This is how quickly the servo can respond and rotate to 60 degrees in either direction. 0.3 seconds may not sound much. However when your racing this can equate to very slow steering left to right. On a nitro car this will result in a slow acceleration and breaking response.
There is not much between 0.30 and 0.19 if you are counting with a stop watch. The effect it has for racing purposes is immense. You will instantly notice a difference. You can go overboard with the speed some servos can go as low as 0.06 seconds. Now this in my opinion is a little over the top, not to mention you can expect to pay over $200 for one.
Speed is important to get the right balance. Too slow and your car will not react quickly enough. Too fast and you car will be zig zagging or hammering on the breaks to hard.
The Hitec HS-7950TH can be operated at 3 different voltages:
- 4.8v = speed of 0.19 seconds.
- 6.0v = speed of 0.15 seconds.
- 7.2v = speed of 0.13 seconds.
You can notice a difference between each of the voltages. My personal favorite is 7.2v its just the right balance and it also gives the servo more torque. 7.2v is referred to as high voltage or (HV) in the industry. Most servos run on 4.8v and 6.0v if you run standard servos and 7.2v you will burn them out.
Why is torque important?
Speed is only half the battle the other highly important aspect to servos is the torque rating. This is essentially how strong the servo is. The larger your rc car is the stronger the servo will need to be.
For 1/8th scale racing I don’t personally like to use a servo which is less than 300 oz-in (21kg). For 1/10th scale 300 oz-in is more than you will ever need even for off road trucks. The only exception to this is if you are looking for a servo to go in a rock crawler. Then you need something above 300 oz-in.
The trouble is if you enjoy this hobby as much as I do and most of my friends, one rc car is not enough. It can get very expensive to purchase a servo for each class of car you have. This is why I like the Hitec servo it’s more than strong enough for anything I can throw at it.
Just like the speed there are 3 different torque ratings depending on the voltage you use:
- 4.8v = 347 oz-in (24kg)
- 6.0v = 403 oz-in (29kg)
- 7.2v = 486 oz-in (34kg)
I think the torque rating of this servo is partly why they last so long. I get roughly 4 years of heavy usage out of the Hitec HS-7950TH.
Hitec HS-7950TH other features.
The Hitec HS-7950TH servo is splash proof. If you are mid race and it starts to rain you will be fine with this servo. I have personally sent mine through some deep puddles. I was determined to win and the last thing on my mind was the servo. While In my case my servo still works with absolutely no issues. There is a reason the manufacturer states splash proof. I would not advise you drive through puddles all the time.
The outer construction is aluminum which has been designed to aid with cooling. The internal gears are titanium and it uses a coreless motor.
Hitec went Hi-Tech (no pun intended) with this servo and added what they call a G2 digital circuit. Just like when you can program a ESC (electronic speed controller) you can program your servo using a program card. I personally don’t use this feature as a lot of the settings are on my transmitter.
You can program:
- Dead Band Width – when your at the race track signals are bouncing around all over the place. You can get spikes in signal changes this allows you to adjust the width of the signal.
- Direction of Rotation – self explanatory useful if you don’t have direction change on your transmitter.
- Speed of Rotation – you can slow the speed down if you wish.
- End Points – set how far the servo is allowed to travel.
- Neutral Points – similar to dead band width but more applicable to transmitter movements. If you don’t like your transmitter to be very responsive this is helpful.
- Fail Safe On/Off – A fail safe is a position you set if your receiver looses signal. I have personally had and seen many cars in the past run away because of signal loss. This happens less with 2.4GHZ systems (some also have fail safes built in).
- Fail Safe Point.
- Resolution – this is how smooth the servo operates. A low resolution slows the servo down with each step slower.
- Overload Protection.