| Pre-Assembly Part 2 |
Last Modified: 2006-10-03
In this step, you will modify the servos to rotate continuously. We have tried several different servo types, weighed the cost, reliability, and ease of modification, and we feel the following is the best servo and modification method for the PPRK.
What is needed to modify a servo.
Start by removing the servo wheel from the servo by loosening the black screw. Take care not to rotate the wheel while loosening the screw.
Next, remove the four long screws from the bottom of the servo. Take care as these screws strip easily.
Remove the lid of the servo. Don't be surprised if a couple of gears either fall out or remain in the lid. Remove them from the lid if they stick.
Remove the small white plastic retainer and the brass bushing. These may be stuck in the gear with the largest teeth. You will be discarding the white plastic piece and replacing the brass bushing with ball bearings.
Now plug the servo into the SV203 controller. Any servo output will do. Make sure to put the darkest servo wire (black or brown) to the outside of the board. Plug the battery pack into the SV203. The servo will likely start spinning. If not, try changing the position of the switch to turn on the power. Adjust the servo until it stops moving by turning the small brass pin (rectangular) that protrudes. This is the potentiometer that typically gives the servo feedback. Here, we disengage it physically from the servo gear (by removing the small white piece) and so the servo rotates continually, thinking it is never reaching the input position. Once the servo stops, you can unplug the battery and the servo from the Pontech controller. Some people suggest using a small drop of cynoacrylate glue on the potentiometer to freeze it in place. We don't do this on the servos we modify so they can be adjusted later but this will ensure they never move.
Now that the servo is modified, you can install the ball bearings. These bearings help the servo take the side loads that the PPRK imposes on it and improve the efficiency, decrease the noise, and lengthen the life of the servo. First, you need to remove the other brass bushing. It is stuck in the lid and needs to be carefully pried out.
The location of the bearing.
Catch it with the point of a small flathead screwdriver and drive it out.
Now, reassemble the gearing and the servo. The order is important here. First, place the bearing on top of the potentiometer. Take care not to move the servo out of adjustment. You also need to clip off the small plastic stop on the large gear.
The bearing goes on first.
Clip the stop from the gear.
Slide on the large gear.
Followed by the middle gear.
Finally, the other bearing is added.
Now, put the lid back on top of the servo. This may be snug and require a bit of finesse as the bearings seat tightly. Plug the servo back into the Pontech along with the battery to be sure the servo is still stationary in the neutral position. If all is well, you are done! You can reinstall the four long screws that hold the servo together. You will probably want to leave the servo wheel off for gluing to the roller wheel in a later pre-assembly step.
Test to make sure it is still adjusted.
Continue on to the next building step .
Review the previous building step .
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