How to Modify a Hitec HS-65HB Servo W/Kryptonite Gears for Continuous Rotation

Presenting the Hitec HS-65HB, one of the the best micro servo's available with Karbonite Gears. So what's so special about this servo? Well how about 31 ounces/inch of torque and 0.11 sec speeds at 6 volts in a compact 23.60 x 11.60 x 24.00mm footprint, Super Strong Karbonite Gears capable of cycles in excess of 300,000 with Zero Wear and almost five times the strength of nylon gears, Top Ball Bearing for smooth and quiet operation, versatile enough for small and large applications, and best of all it's extremely easy to modify for continuous rotation. This is one servo Futaba, GWS and JR can't touch. A micro monster with whopping torque/speed and if you can afford the $21.00 price then you can't go wrong for the quality/durability you get with this fine product. So why bother with extra torque in a compact unit and not just get a cheap servo instead? Well let me give you an example. Torque complements speed and let's say you have a mobile robotic platform using cheap micro servos for drive. As you begin to add weight (eg. batteries, sensors, controllers) your platform begins to suffer and the speed is heavily decreased, not to mention the excess strain on those weak nylon gears. Having that extra torque output and the Karbonite gears gives you an advantage, the boost your platform needs to counter the effects of weight and keep it moving. This servo gets it done and does a fine job in its modified continuous rotation form. So how easy is it to modify? So easy that you only need to touch one gear. That's Right! No extracting of PCB boards, replacing of potentiometers with resistor networks or even cutting a single wire. Don't even mess with the electronics and save your servos in case you want to return to standard servo performance (see step 7). Why the steps are so easy you could just follow the photos. But please do read for "reading is knowledge" and well worth it. With that said, let's begin....................

Step 1: Tools Required

To perform this modification, you will need these tools:

1 x Phillips Screwdriver
1 x Precision Screwdriver 1.0m/m
1 x Needle Nose Plier
1 x Wire Cutter
1 x Drill
1 x Drill Bit 1/16"
(Optional) Small Hand File OR Sandpaper

Step 2: Removing the Almighty "X" Horn

Use a phillips screwdriver and remove the horn on your servo.

Step 3: Unscrew the Case and Lift Off the Top

Using a small precision screwdriver remove the 4 screws beneath the case. Do this slowly as the screws have a tendency to strip easily. Now carefully lift off the top section of the case while paying attention to gear orientation. All gears should come out of the top section. If not, then just pull out any gears that have not remained intact. Also, if you suffer from "very short term memory" this would be a good time to take a snapshot of the gear orientation using a digital camera so you can reassemble everything back without going crazy. Trust me, It actually gets worse with smaller servos.

Step 4: Pull Off Main Gear and Cut the Stop Tab

Now with the case off, pull off the main gear. It is actually push fitted onto the D shaft of the potentiometer. Just pull it off and cut the stop tab. You can use a file or sandpaper to shave down the tab until flush but not necessary if you cut low enough. You will also notice the second gear on the left side of this image will already be loose and that's because it's shaft is inside the top section of the servo you removed in the previous step.

Step 5: Hold Top of Main Gear and Drill Completely Through Using a 1/16" Bit

Now you will need to drill through the main gear with a 1/16" bit. If using a high RPM drill, say about 1000 RPM's, you can simply hold the gear in you hand, but start the drill before you enter the gear. For slower RPM drills, I recommend holding the main gear firmly on the top half section only, where the servo horn aligns using a needle nose plier. 'Do Not Apply Too Much Force As That Can Damage the Teeth!' Just enough to hold it stable and prevent any turning. Also, 'Never Hold The Bottom Of The Main Gear While Drilling' You do not want to risk damage to the drive of the geartrain.

Step 6: You Are Done! Now Reassemble Your Servo.........

You Are Done! Follow the steps on the image and reassemble the servo in the order shown. So how easy was that?

Please Note: If you want the servo to make a complete stop you will need to glue the potentiometer. You can do this now before reassembling by removing the gear that sits right under the Main Gear on the potentiometers shaft. Next using the needle-nose pliers turn the shaft left-to-right until you find the center point. Now just apply a little hot glue for a (non-permanent) modification. You can then simply pry the glue off if you wish to revert to standard servo performance someday (See Step 8).

Step 7: You Now Have a Continuous Rotation Servo. So Give It a Test Spin

You have now converted your servo into Continuous Rotation without damaging or tampering with any of the electronics or the cuitting of a single wire. It does not get better than this! Here is some sample Basic code to give it a test spin at various speeds in both directions. Commands may differ slighly for each servo.

Please Note: If you want the servo to make a complete stop you will need to glue the potentiometer. You can do this by removing the gear that sits right under the Main Gear on the potentiometers shaft (See Step 6). Just apply a little hot glue for a (non-permanent) modification. You can then simply pry the glue off if you wish to revert to standard servo performance someday (See Step 8).
The "Stop" command can be found through trial-and-error if you glued your potentiometer as mentioned in Step 6.

'Servo Pin, Speed/Direction'

Servo 0, 99 (Very Slow Left)
Servo 0, 103 (Very Slow Right)
Servo 0, 95 (Slow Left)
Servo 0,105 (Slow Right)

Servo 0,80 (Very Fast Left)
Servo 0,130 (Very Fast Right)
Servo 0, 90 (Fast Left)
Servo 0,115 (Fast Right)

Step 8: Purchase a Replacement Main Gear and Return Your Servo to Standard Performance

Now comes the most awesome benefit. The best of both worlds. Just purchase yourself a set of replacement gears and simply install a new main gear and you're right back to standard servo performance. Remember, the main gear is push fitted onto the "D" shaft of the potentiometer so there is no chance for misalignment. It can only be inserted the correct way. Just too good to be true right? Hope you enjoyed this conversion..............