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Old 11-21-2010, 12:06 PM   #1
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Default losi throttle trouble......need help

I have a losi 2.0. I have had the car for a month and have gone through 3 servos in one month. the servos are not cheap ones (hitec 7955, hitec 7945, airtronics 759, and a specktrum 6040). I have had 5, 2.0 and have had the same issue with 2 others. I have tried every trick that worked on the other 2 chassis and it still burns out servos. The last one burned out in 15 mins. I have followed the adendum to a T, twice and still no luck. any help would be nice. I am tired of not being able to finish a race due to this issue.
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Old 11-21-2010, 12:48 PM   #2
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Hey Just a couple things to double check.

Make sure your linkages are setup straight and not binding. The throttle has to be parallel to the chassis or it will pull the servo towards the engine and cause the bottom of the servo to hit the chassis guard. Add even a slight impact when the servo is bound up and then the chassis flexes and your servo is TOAST.

Make sure you aren't putting too much stress on your servos by not properly adjusting your epa's you definitely NEVER want the servo to stall on the throttle side and you don't need nearly as much braking as you might think. You only want enough brake to make it difficult to turn the center diff with your thumb.

I would also take a minute or two and dremel out the chassis guard so that there is no chance at all that the servo can ever touch it. I bet if you look right now it less that 1mm from rubbing!

Make a note to double check the linkage and servo clearance any time you change your servos!

When I first started with my 8IGHT-T 2.0 I went through the stock servo in about a gallon
After that I switched to Hitec 7955-TG's for the throttle and burned up three of them within the next gallon because they were hitting the chassis guards with perfect EPA's and correctly setup linkages. I have since dremeled out the chassis guards and been problem free for about 5 gallons.
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Old 11-21-2010, 01:22 PM   #3
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Quote:
Originally Posted by ghost68 View Post
Hey Just a couple things to double check.

Make sure your linkages are setup straight and not binding. The throttle has to be parallel to the chassis or it will pull the servo towards the engine and cause the bottom of the servo to hit the chassis guard. Add even a slight impact when the servo is bound up and then the chassis flexes and your servo is TOAST.

Make sure you aren't putting too much stress on your servos by not properly adjusting your epa's you definitely NEVER want the servo to stall on the throttle side and you don't need nearly as much braking as you might think. You only want enough brake to make it difficult to turn the center diff with your thumb.

I would also take a minute or two and dremel out the chassis guard so that there is no chance at all that the servo can ever touch it. I bet if you look right now it less that 1mm from rubbing!

Make a note to double check the linkage and servo clearance any time you change your servos!

When I first started with my 8IGHT-T 2.0 I went through the stock servo in about a gallon
After that I switched to Hitec 7955-TG's for the throttle and burned up three of them within the next gallon because they were hitting the chassis guards with perfect EPA's and correctly setup linkages. I have since dremeled out the chassis guards and been problem free for about 5 gallons.
I know my epa a asjusted correctly. I make sure that there is at least 1/16 movement on wot. and that there is 6.5mm movement on the full brake side. the radio stray does not move at all from one full swing to the other. The last servo was to hot to touch when it went out. Thank you for the insight.
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Old 11-21-2010, 03:07 PM   #4
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the original throttle servo death trap, at least one losi per race does not finish. i know a guy that put a $14 servo for throttle just to get him by and its lasted the longest while he is waiting on 2 to come in from warranty. just threw it in there too, no linkage check or anything. he does not want to touch it now.
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Old 11-21-2010, 05:38 PM   #5
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I too have had some throttle servo troubles. I have burn out 2 7950's. Thankfully neither cost me a main finish. I really cant believe it since these are supposed to be the best servos on the market. I tried to use the grommets on them but they raised the servo to high. Does anyone grid off the risers on the tray so you can use grommets plus keep the linkage level?
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Old 11-21-2010, 06:03 PM   #6
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Originally Posted by j_blaze14 View Post
the original throttle servo death trap, at least one losi per race does not finish. i know a guy that put a $14 servo for throttle just to get him by and its lasted the longest while he is waiting on 2 to come in from warranty. just threw it in there too, no linkage check or anything. he does not want to touch it now.
Good thing about some of the older style analog servo's, even stalled many don't draw enuff current to burn up.
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Old 11-21-2010, 06:28 PM   #7
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I agree about the analog, but it must be possible to use a digital. Drake uses a hitec 7900 series for thottle.
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Old 11-21-2010, 06:57 PM   #8
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Quote:
Originally Posted by ohiostatechamp View Post
I agree about the analog, but it must be possible to use a digital. Drake uses a hitec 7900 series for thottle.
I have only used digitals for years. The only time I have burned one up is when I failed to turn the car off in the pits with the radio off and I had the failsafe set for full brakes. Burned a hole right thru the case and caused a lot of excitement. Other than that just install them correctly and get the end points set right.
One other thing on the Losi that I did not see mentioned yet, make sure the carb is turned so the slide does not get into the rear brake.
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Old 11-21-2010, 07:31 PM   #9
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To understand how to prevent servo failure you have to understand why they fail

Losi has chosen to have a radio tray instead of a radio plate like a lot of other manufacturers. This makes life easier when maintaining your kit but it causes all kinds of problems because of how flexible the plastic is. This tray flexes like crazy when you’re out on the track and if your EPA’s and linkages aren’t just right the radio tray flexes even more. When the tray flexes it literally twists the gears inside the servo causing them to bind up and then either strip or fry the motor driving them. In addition to radio tray flex causing servos to bind up inside the servos it also causes the servos to flex from side to side and can cause the servos to hit the side guards on the chassis or even worse the chassis itself. If your servo suddenly hits the chassis or side guard it can put an extreme load on already bound up gears and now you are really asking for trouble.

Servos only have to be made to a specific length and width for the mounting holes. Contrary to what you may believe the shims that you have to use with different brands of servos are not to keep the servo in line with your carb and brakes but instead to keep the servo from bottoming out on the chassis. This is why "cheap" servos seem to last longer they are generally shallower because they lack the digital circuitry. A shallow servo doesn’t bottom out and isn’t really affected by chassis flex so they seem to last longer.
To add to this problem there are two available chassis options for the 8IGHT and 8IGHT-T. The RTR chassis and then there is the "Flex Tuned Chassis" the difference between the two is that the Flex tuned chassis has cutouts to give the servos more vertical clearance and that helps keep the servos from bottoming out during chassis flex. Yes you are more likely to burn up more servos if you don’t upgrade to the better chassis.

There are so many theories/fixes at my track and everyone has problems. I believe that there are a few major variables here that cause these servos to fail. Any of the items listed below can cause a servo to fail by itself and the effect is only compounded when there more than one thing is wrong.

1.) EPA's… If your servos are pulling so hard that your radio tray flexes you are doing it wrong. Losi has a very specific guide for this on their website and I have summarized it a few posts above this one. If you are causing your radio tray to flex on the bench then it is only amplified out on the track with chassis flex. Everyone says their epa’s are correct and they still fry servos… Keep Reading…

2.) Improper Carb Alignment... This one is probably the most overlooked that I see, if the throttle linkage isn't perfectly parallel to the chassis it will cause the gears inside the servo to bind up. Add this to the chassis flex from hitting those jumps at full throttle and then boom your servo fries because it bottoms out or hits the side guard.

3.) Not enough clearance around the servos… This is the one that no one seems to know about. While it is really easy to make sure that your EPA’s and linkages are perfect you probably wouldn’t think to see if your servo is touching anything… Chances are that if you have replaced your stock servos with something more expensive your servo is already touching the side guard or the chassis. This is especially the case if you are on your second or third high end servo in less than a gallon or two of fuel. Chassis flex will cause your servo to fail extremely fast if the servo is in direct contact with the chassis or side guard. Servos are not designed to handle the extreme vibration and shock that your chassis goes through. I had several 7955tgs burn up within 15 minutes of being on the track because they were touching the side guard. Fortunately there is a pretty easy fix for this; use shims to keep the servo from touching the chassis and if the servo is touching the side guard you just cut away where it touches the servo and problem solved.

4.) All electronics can die for no reason at any time… Yea blame god for this one even with everything perfect a servo can just die for no reason... Not a lot you can do about this one…

If you don’t check all of the above every time you change a servo then you can expect to spend a lot of time mailing your servos in for service.
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Old 11-21-2010, 08:45 PM   #10
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Default savox

this is not being biast or anything.

best thing to do with a losi radio tray is to put in a Savox SC-1258TG servo.
digital 12kg, AND its not as tall as the other standerd size servos, your left with about 3mm from the chassis and guard.

i tryed that and so far good luck after like 8 months... have recently put in a KHDZ radio tray stiffner to remove the radio tray flex.(hasnt effect performance at all)

and my alpha cant have its carb ball turned around so my throttle rod linkage is on a 45DEG angle mybe more. no problems at all.
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Old 11-21-2010, 08:57 PM   #11
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Quote:
Originally Posted by 808gx7r View Post
this is not being biast or anything.

best thing to do with a losi radio tray is to put in a Savox SC-1258TG servo.
digital 12kg, AND its not as tall as the other standerd size servos, your left with about 3mm from the chassis and guard.

i tryed that and so far good luck after like 8 months... have recently put in a KHDZ radio tray stiffner to remove the radio tray flex.(hasnt effect performance at all)

and my alpha cant have its carb ball turned around so my throttle rod linkage is on a 45DEG angle mybe more. no problems at all.

Is your a 1.0 Losi? I didn't think the King Headz tray stiffners worked on the 2.0's. I have one from my 1.0 but never ran it. Didnt think the holes lined up and didnt really want to dremel off the spacers on the 2.0 tray.
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Old 11-21-2010, 09:40 PM   #12
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Could be the carby slide binding.

I use the stock losi motor and I found that the throttle return spring was pulling the slide to one side as there is a bit of play in them slides.
The slide needs to be centered but the spring can pull it up or down depending where the spring is pulling it and making it bind.

Mine ran months without any problems and then one day the whole tray was getting pulled over using my 403 oz servo and this was during a race day.So make some adjustments and see what happens.
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Old 11-21-2010, 09:45 PM   #13
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Is your a 1.0 Losi? I didn't think the King Headz tray stiffners worked on the 2.0's. I have one from my 1.0 but never ran it. Didnt think the holes lined up and didnt really want to dremel off the spacers on the 2.0 tray.
made it fit

AND check out the angle on that linkage... as long as the servo horn to the rod isnt tight its fine and has been like that for months
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Old 11-21-2010, 10:19 PM   #14
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The servo tray flexes diagonally across the throttle servo pod.

I lost 3-Hitecs this year before realizing the tray just needs bracing.

I wound up using some carbon fiber scrap and making two braces. One on the inboard side of the servo and one longer one on the outboard side.

Works similar to the old KingHeadz brace. Haven't lost servo since.
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Old 11-21-2010, 11:16 PM   #15
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Quote:
Originally Posted by 808gx7r View Post
made it fit

AND check out the angle on that linkage... as long as the servo horn to the rod isnt tight its fine and has been like that for months
To me it looks like your carb needs twisted to straiten up that angle on your throttle linkage. I have to have my throttle arm at almost a perfect 90 deg off the servo horn, as most guys do. That angle just looks wrong. But hey if it works , great. So you dremeled off the tabs on the servo tray to except the tray stiffner? And did the holes line up?
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