majorheli
Heliman
Location: Stow, MA
| My two brothers have the tethered models. My older brother had some servo lag issues on the roll servo. Here are his observations:
"The servos are not sold as a repair part.
I think age, use and the short travel this servo has all contribute to its response demise. After finding that you can't get them as a replacement part and not finding much for "salvage parts" on eBay, I wouldn't recommend doing what I did to get my roll servo livened up again. If I had damaged the pot, motor or planetary gear reduction while re-working it, I would have been S.O.L.
I am still considering whether to revise the circuit on the Tx signal processing board. If the circuit components weren't all surface mount it wouldn't really be much of a challenge. I could replace the one fixed resistor that is different in the roll stick signal from the same resistor in the pitch stick signal with a variable pot. But I think I may have figured out why they have half the rate on the roll servo as the pitch servo in the first place.
I think the key to it is how they use the two servos to move the swash plate. To get the MR(main rotor) pitch to work in its cyclic function purely, the swash plate must move at right angles linearly. When the pitch servo wheel rotates, it closely approximates linear movement of the swash plate because it pivots on the roll servo's arm screw. The slot in the swash plate arm doesn't t let the rotary motion of the pitch servo to get into the arm.
However, when you rotate the roll servo wheel it pushes and pulls the swash plate at about right angles to the pitch servo's movement. But as the roll servo wheel rotates farther its movement of the swash plate starts to give it displacement in the pitch direction as well. So my theory is that if you had more roll servo wheel rotation, you would start to get pitch cyclic into the swash plate causing the heli to both roll and pitch. The question then becomes "how close are the roll servo travel endpoints they chose to producing detectable pitch coupling?".
The elegant fix for Hirobo would have been to develop a non-linear mix of the roll servo to the pitch servo so that as the roll servo wheel provided more pitch displacement into the swash plate, the roll servo would be moved to counteract that displacement.
If I am correct about this "flaw" in Hirobo's swash plate concept for the Lama, then all the wireless models, including the knockoffs (as well as Helihobby's XRB wireless conversion) should suffer this problem."
Tony |
