Servo arm help needed
08-22-2003, 02:53 PM
#1
Servo arm help needed
Hi all, I have a question that is probably laughable to most of you. 
I'm new to R/C Cars (4 days new in fact) and I bought a Duratrax RTR Evader ST, thats not the laughable bit btw
I used about 6 packs and then crashed it into a rock, which promptly stripped one of the servo gears.
I decided that as the nylon teeth broke so easily I would get a servo with metal gears and I went out and bought myself a Hitec 645MG thinking that it would be just the job.
Unfortunately the servo arm that came with the truck just slips on the servo output spline when I try to stear.
The servo output spline is just a bit too small to mesh properly with the arm.
Is there anyway that I can fix this without resorting to something permanent like gluing or putting a pin through the arm and the servo spline?
Any help or suggestions would be greatley apreciated.
Steve.
I'm new to R/C Cars (4 days new in fact) and I bought a Duratrax RTR Evader ST, thats not the laughable bit btw
I used about 6 packs and then crashed it into a rock, which promptly stripped one of the servo gears. I decided that as the nylon teeth broke so easily I would get a servo with metal gears and I went out and bought myself a Hitec 645MG thinking that it would be just the job.
Unfortunately the servo arm that came with the truck just slips on the servo output spline when I try to stear.
The servo output spline is just a bit too small to mesh properly with the arm.
Is there anyway that I can fix this without resorting to something permanent like gluing or putting a pin through the arm and the servo spline?
Any help or suggestions would be greatley apreciated.
Steve.
08-22-2003, 07:13 PM
#2
Your problem is easy enough to solve, but I think you should understand it a bit first.
Okay, the servo that comes with your truck is produced by Futaba, while you have purchased a servo made by Hitec. Unfortunately, these servos' spline's are actually different. The Futaba has a 25 toothed spline, while the Hitec has a 24 toothed spline. So there was no way that the stock servo horn from the Duratrax kit would have worked properly with your new Hitec servo.
So the solution is to buy a servo horn that is made especially for the Hitec servo. Bring in your servo, along with your truck to your local hobby shop, that way they can help you sort out any confusion, because you can't use just any servo horn for your application.
Okay, the servo that comes with your truck is produced by Futaba, while you have purchased a servo made by Hitec. Unfortunately, these servos' spline's are actually different. The Futaba has a 25 toothed spline, while the Hitec has a 24 toothed spline. So there was no way that the stock servo horn from the Duratrax kit would have worked properly with your new Hitec servo.
So the solution is to buy a servo horn that is made especially for the Hitec servo. Bring in your servo, along with your truck to your local hobby shop, that way they can help you sort out any confusion, because you can't use just any servo horn for your application.
08-22-2003, 11:06 PM
#3
Tech Addict
Join Date: Aug 2001
Location: In the pits throwing wrenches at slow cars!
Posts: 548
Gearstripper,
You'll have to check that the servo-saver that is built into the steering system is operating properly as well. It's a spring-loaded device that takes the shock of impact so that the servo gears don't strip...
The pre-load on the spring can be adjusted by threading the nut on the bellcrank up (less preload, more protection and if too loose can lead to less direct steering response) or down (more preload, less protection and more direct steering response). Your local hobby shop should be able to help you get it set properly while you're getting a new output arm. The spring needs to be set soft enough to give the protection to the servo (metal gear servos are not imune to gear failure) and stiff enough so as to not compress under normal driving loads. Hitting anything bigger and or heavier than your truck is not normal driving but hey...it happens!
It's unfortunatly just one of those things that you learn from experience. If the hobby shop can't help you head out to a track near you on a race day. Most racers are more than willing to help a beginner out.
Good luck!
You'll have to check that the servo-saver that is built into the steering system is operating properly as well. It's a spring-loaded device that takes the shock of impact so that the servo gears don't strip...
The pre-load on the spring can be adjusted by threading the nut on the bellcrank up (less preload, more protection and if too loose can lead to less direct steering response) or down (more preload, less protection and more direct steering response). Your local hobby shop should be able to help you get it set properly while you're getting a new output arm. The spring needs to be set soft enough to give the protection to the servo (metal gear servos are not imune to gear failure) and stiff enough so as to not compress under normal driving loads. Hitting anything bigger and or heavier than your truck is not normal driving but hey...it happens!
It's unfortunatly just one of those things that you learn from experience. If the hobby shop can't help you head out to a track near you on a race day. Most racers are more than willing to help a beginner out.
Good luck!
08-23-2003, 07:18 AM
#4
Thanks alot guys,
I took the truck to my LHS and they showed me how to do the servo horn, I actually got the right part with the servo (big red X
) but I didnt realise I what I had to do.
The guy in the LHS drilled one of the holes bigger so the ball connector off of my old servo horn fitted (put a small nut on the back, making sure it didn't rub at all) and cut off the extra horns so that it fitted in the truck. I know you guys know how to do this, but I thought I would say incase anyone else had the same problem as I did.
They also told me that the servo saver was set much too tight (there was no play on it at all, may aswell have not been there)and loosened it
Thank you again guys, helped me alot, I can now get back to driving into big rocks again
Take care and have fun!
Steve
I took the truck to my LHS and they showed me how to do the servo horn, I actually got the right part with the servo (big red X
) but I didnt realise I what I had to do.The guy in the LHS drilled one of the holes bigger so the ball connector off of my old servo horn fitted (put a small nut on the back, making sure it didn't rub at all) and cut off the extra horns so that it fitted in the truck. I know you guys know how to do this, but I thought I would say incase anyone else had the same problem as I did.
They also told me that the servo saver was set much too tight (there was no play on it at all, may aswell have not been there)and loosened it
Thank you again guys, helped me alot, I can now get back to driving into big rocks again
Take care and have fun!
Steve
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