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Model Forum / Radio Controlled / Land Models / September 2005RC18MT Servo Steering Wanders
I recently got a Team Associated RC18MT. Before I had finished my first battery charge something happened to the steering servo, and had to be replaced (due to hard impact with a kerb). I just put in a new one last night. Everything looks good, but for this weird and annoying behavior: When I hold it in my hand (in the air) and turn the steering to either side and then let it go back to center, after it gets to center the servo gently wanders slightly left/right a little before finally settline down maybe 15 seconds later. The position is settles down in varies from left to right. Therefore when I'm driving it sometimes it goes straight, sometimes it pulls left and sometimes it pulls right. It's very annoying. What could be the source of this problem and how can I fix it? Thanks, AA >I recently got a Team Associated RC18MT. Before I had finished my first >battery charge something happened to the steering servo, and had to be [quoted text clipped - 13 lines] > > AA What kind of servo did you replace it with? Doc "Doc" wrote: >>I recently got a Team Associated RC18MT. Before I had finished my first >>battery charge something happened to the steering servo, and had to be [quoted text clipped - 17 lines] > > Doc same as the original. > "Doc" wrote: >> [quoted text clipped - 21 lines] > > same as the original. Sounds like there is some binding in the steering somewhere close to center that the servo can't overcome on it's return to center. The servo is at it's weakest at and just off from center, so even a little binding will cause it to dance around like that. To test this theory, disconnect the steering linkage from the servo and see if the servo does it with just the horn attached. Doc "Doc" wrote: >>"Doc" wrote: >> [quoted text clipped - 30 lines] > > Doc When I had the servo out the steering seemed OK, loose I mean. Can I just pop the plastic arm off of the part (servo saver?) connected to the servo? I'm afraid the plastic will snap. I bought this pre-built so don't know exactly how everything is held together. AA > When I had the servo out the steering seemed OK, loose I mean. Can I just > pop the plastic arm off of the part (servo saver?) connected to the servo? > I'm afraid the plastic will snap. I bought this pre-built so don't know > exactly how everything is held together. > > AA Yes, that is what I meant. Doc This is normal behavior for the 18MT. The servo saver spring is fairly weak and stretches. Once stretched it does not have the force to shove the steering to center. If your racing, or this bothers you regardless, you need to beef up your spring, or replace the servo saver with a different type. Some people have had luck tightening the origial spring, but that is only a temporary fix as one good jolt stretches it again. Keep in mind you can never fix problems in an RC vehicle, just move them. A stronger spring can result in a broken servo where the original spring might not. I hope you got a metal gear servo this time. Check out www.one18th.com. This is a great resource for the 18MT and you can see numerous fixes for the wandering sterring detailed there. Now if only I could fix the exposed gears as easily..... > Keep in mind you can never fix problems in an RC vehicle, just move > them. This is, perhaps, the most profound quote I have ever heard! (Not flaming, being dead serious here). It is VERY true in most instances. Making another parts stronger just transfers the "trauma" elsewhere in the event of heavy-handed driving or a collision. There is always going to be a weak link somewhere. Doc > > Keep in mind you can never fix problems in an RC vehicle, just move > > them. [quoted text clipped - 7 lines] > > Doc Thats right, but when you think of the abuse the things take, its no wonder that they eventually break! This is the main reason I keep heaps and heaps of spares for the most common breakages, but still manage to have downtime like I do atm with my E-maxx. (but when the replacement axle set arrives, I'll have 7 spare axles!) Bash ON! Cheers Dre > This is normal behavior for the 18MT. The servo saver spring is fairly > weak and stretches. Once stretched it does not have the force to shove [quoted text clipped - 12 lines] > you can see numerous fixes for the wandering sterring detailed there. > Now if only I could fix the exposed gears as easily..... A guy at one shop said something about a spring too, and I have to admit I'm puzzled. I've seen no spring or anything spring-like in the whole assembly. Is this perhaps inside the other rotator opposite the servo? I sure didn't notice it when I had the servo out, but maybe I wasn't focused on it. I'm not sure I understand the theory, though. The spring should try to bring it back to center, and the servo also wants to be centered, so why would a weak spring cause it to travel left and right once it's already centered? Seems like once it is centered both the spring and the servo should be at peace. Could it be that I had some tension on the elusive spring when I put the servo in the other side? Keep in mind that it does this even when I am holding it in the air -- there is no friction from the ground. Thanks guys. AA It looks like a plastic letter "C", not a coil spring like the shocks. Wonder if I can explain how it works? There are two round pieces with tabs that fit in the open part of the C. It looks like a sandwhich, roud piece with tab at top on servo, C with opening on top, round piece with tab at top for steering. When new the opening is just big enough to fit both tabs and the C is strong enought to keep them aligned under normal conditions. Servo moves the C, C moves the steering piece. If you hit something, the C expands, and allows the steering to move more then the servo does and keeps the servo from breaking. The C should then close back up and get the two tabs back in alignment. What happens is the C gets weak and does not have the strength to get the tabs back in alignment. The force of the servo is enough to stretch the C, even without a collision. This is a very common servo saver design and I have been using them for years without this problem so don't look for another style of servo saver to solve the problem. It is a material flaw on AEs end, the C is simply made of the wrong type of plastic. Remove the servo saver and take it apart. Find the C and squeeze it tight with plyers, make it smaller. Put it back on, it should be tighter now, and while holding it see if the problem is better then it was. If so, then you know for sure you found the problem. |
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