R/C Tech Forums

Go Back   R/C Tech Forums > General Forums > Nitro Off-Road

Reply
 
Thread Tools Search this Thread
Old 12-05-2006, 11:32 AM   #976
Tech Champion
 
Davidka's Avatar
 
Join Date: Oct 2004
Posts: 9,846
Trader Rating: 75 (100%+)
Default

It's supprising to hear complaints about chassis flex on a car with a chassis that's 1mm thicker than anything out there. Are you guys sure it's a problem?
__________________
"I have no idea what you're talking about, so here's a bunny with a pancake on it's head."

In mind and body, we're all heading towards old age. It is slower to go by bike.
Davidka is offline   Reply With Quote
Old 12-05-2006, 11:46 AM   #977
Tech Fanatic
 
Join Date: Aug 2002
Location: Chicagoland (southwest suburbs)
Posts: 795
Trader Rating: 2 (100%+)
Default

Quote:
Originally Posted by Davidka
It's supprising to hear complaints about chassis flex on a car with a chassis that's 1mm thicker than anything out there. Are you guys sure it's a problem?
Because there is essentially no structural 'upper deck' on this car, they are relying almost entirely on the strength of the chassis to prevent chassis flex.

It's the difference between bending a piece of flat plate verses an I-beam. The I-beam acts nearly like a flate plate that is as thick as the distance between the two flanges (lower chassis and upper deck in the case of our cars).

I have not had a throttle servo fail yet, but I can see that this car bends more than my old OFNA did, and I can see that this bending puts a lot of mechanical stress on the throttle servo's case, and I can see that my body mount holes are much more 'elongated' on this car than any of my previous cars.

Maybe this flex is good for handling, I don't know, but it 'might' be causing some of the servo issues.
__________________
SpeedPassion, SpeedPower, ProLine Racing
Losi 8ight, Losi SCTE, AE SC10, AE RC10T4, Kyosho IGT
Walt is offline   Reply With Quote
Old 12-05-2006, 12:05 PM   #978
Tech Elite
 
Join Date: Nov 2003
Location: Covington, La.
Posts: 3,585
Trader Rating: 50 (98%+)
Send a message via AIM to micrors4guy
Default

i dont think flex is killing all the servos. also the flex in the car iswhat makes the car handel soo well thres the rought.
__________________
Rob Jensen
Thanks to the following companies for their support in 2017: Team Associated, Maclan, Fierce R/C Solutions
micrors4guy is offline   Reply With Quote
Old 12-05-2006, 12:20 PM   #979
Tech Fanatic
 
Join Date: Aug 2002
Location: Chicagoland (southwest suburbs)
Posts: 795
Trader Rating: 2 (100%+)
Default

Quote:
Originally Posted by micrors4guy
i dont think flex is killing all the servos. also the flex in the car iswhat makes the car handel soo well thres the rought.
Flex killing servos is just a theory based on observation, and it's difficult to prove or disprove (especially since I have not had a servo failure yet myself).

And the flex might, indeed, be good for handling.

But if the chassis is flexing enough to alter handling, then in order for that flex to happen, something has to 'give' on the upper deck, and that includes the throttle servo.

Has anyone gotten word back from a servo manufacturer regarding the nature of the failure of their throttle servo? 'Burn out', to me, would indicate an end-point misadjustment or some other 'overload' condition. Parts broken on the circuit board would indicate to me that there is stress on the servo case that's being transmitted to the printed circuit board.

It would be an interesting question to ask.
__________________
SpeedPassion, SpeedPower, ProLine Racing
Losi 8ight, Losi SCTE, AE SC10, AE RC10T4, Kyosho IGT
Walt is offline   Reply With Quote
Old 12-05-2006, 12:23 PM   #980
Tech Champion
 
Davidka's Avatar
 
Join Date: Oct 2004
Posts: 9,846
Trader Rating: 75 (100%+)
Default

It's true that there is no upper deck on this car but there is not on nay other current 1/8 either. While the rear chassis brace on other cars is longer most US drivers find that using the softer ball end or plastic braces is the hot setup. All this on 3mm chassis plates. It should also be noted that an early complaint was the small overlap between the center drive shaft and the center diff outdrive was very shallow there have been no dogbones walking out. I have cased my car HARD several times (this would cause the reverse chassis flex that would cause the dogbone to come out) and no problems whatsoever. My Mugen was not nearly as stiff as the 8ight in terms of chassis flex. I think the chassis flex/servo thing may be a witch hunt but there may be something to the radio tray being soft. Perhaps carefully opening the servo mount at it's ends to allow for a touch of flex wouldn't be a bad idea?
__________________
"I have no idea what you're talking about, so here's a bunny with a pancake on it's head."

In mind and body, we're all heading towards old age. It is slower to go by bike.
Davidka is offline   Reply With Quote
Old 12-05-2006, 12:30 PM   #981
Tech Fanatic
 
Join Date: Aug 2002
Location: Chicagoland (southwest suburbs)
Posts: 795
Trader Rating: 2 (100%+)
Default

Agreed, but there is one more thing that I think is unique to the 8ight (and correct me if I'm wrong)... the 'upper deck' on the 8ight only passes by the throttle servo along one side, not both. So, any force being transmitted through the upper deck will tend to 'squeeze' or 'compress' the throttle servo much more than if the deck wrapped all the way around the throttle servo.

Are there any other cars that share that design?

And just to be clear, I agree that this theory might indeed be a witch hunt, but it is, I think, an interesting observation, and I have yet to hear a better explanation as to why this particular car seems to fail more throttle servos than other cars.

End point adjustments, I think, account for most servo failures, but it seems like the people experiencing throttle servo failures know what they are doing, but again, I have not failed a servo (and I know my end points are good).

I also have not raced outdoors yet, where the crash impacts are probably MUCH greater than on a smaller indoor track.
__________________
SpeedPassion, SpeedPower, ProLine Racing
Losi 8ight, Losi SCTE, AE SC10, AE RC10T4, Kyosho IGT
Walt is offline   Reply With Quote
Old 12-05-2006, 12:43 PM   #982
Tech Master
 
SCUBA STEVE's Avatar
 
Join Date: Aug 2004
Location: Ohio
Posts: 1,836
Trader Rating: 85 (99%+)
Default

Saturday night I bottomed out my 8 off a big jump (HARD!!) and the Throttle servo quit immediatly.......(the servo did'nt hit the bottom of the chassis)......put another one in and ran the third heat and it did it again in warm up laps...... two $110 dollar servos with in an hour of each other.
Granted I have been racing the eight ALOT! since it's release and this is my first servo problem, so I'm not complaining just trying to give you guys more clues
SCUBA STEVE is offline   Reply With Quote
Old 12-05-2006, 12:49 PM   #983
Tech Champion
 
Davidka's Avatar
 
Join Date: Oct 2004
Posts: 9,846
Trader Rating: 75 (100%+)
Default

Man Steve, that SUCKS! I would be very frustrated (you probably are).

If flex is the culprit then we should be seeing servos with broken cases or ears broken off too.

I think the flex in the tray is as much about the material it's made of as it's not surrounding the servo. When I first put my servo in (Air 258, hope it lasts...) it flexed the tray a lot before I adjusted the EPA's. I was lucky to notice the excess spring length right away.
__________________
"I have no idea what you're talking about, so here's a bunny with a pancake on it's head."

In mind and body, we're all heading towards old age. It is slower to go by bike.
Davidka is offline   Reply With Quote
Old 12-05-2006, 12:51 PM   #984
Tech Fanatic
 
Join Date: Aug 2002
Location: Chicagoland (southwest suburbs)
Posts: 795
Trader Rating: 2 (100%+)
Default

Quote:
Originally Posted by SCUBA STEVE
Saturday night I bottomed out my 8 off a big jump (HARD!!) and the Throttle servo quit immediatly.......(the servo did'nt hit the bottom of the chassis)......put another one in and ran the third heat and it did it again in warm up laps...... two $110 dollar servos with in an hour of each other.
Granted I have been racing the eight ALOT! since it's release and this is my first servo problem, so I'm not complaining just trying to give you guys more clues
When you send those in for repair, send a note explaining what happened and ask them to try to find the root cause of the failure. We might be surprised by what they have to say.

And remember that servo cases can bend quite a bit before breaking, but circuit boards are very brittle. I can easily see the internal circuit board failing WAY before we'd see external damage to the case of the servo.
__________________
SpeedPassion, SpeedPower, ProLine Racing
Losi 8ight, Losi SCTE, AE SC10, AE RC10T4, Kyosho IGT
Walt is offline   Reply With Quote
Old 12-05-2006, 01:40 PM   #985
Tech Master
 
SCUBA STEVE's Avatar
 
Join Date: Aug 2004
Location: Ohio
Posts: 1,836
Trader Rating: 85 (99%+)
Default

Yea, the bad thing is , (like you guys were saying) I beleive the car benefits from flexing and that is why it handles so well .... I remember when I used to race electric, I hated running the graphite chassis on my xxx buggy because it just did'nt handle as well as the plastic one..... I hope that the 8 will still handle well with the aluminum chassis braces I just put on.

Another thing on that note: Everyone says that this car get's better as you run it more and more which I think is true..... but that may be because the plastics are starting to get the flex in them after a few bumps and jumps. I noticed that my plastic chassis braces will now stretch back and forth......But I'll tell you what the car might be hard on some of the internals but I really beleive the car itself is Indestructable!....(I probably should'nt of said that! ...Knock on wood)!!!
SCUBA STEVE is offline   Reply With Quote
Old 12-05-2006, 02:04 PM   #986
Tech Elite
 
Join Date: Nov 2003
Location: Covington, La.
Posts: 3,585
Trader Rating: 50 (98%+)
Send a message via AIM to micrors4guy
Default

scuba steve- i have to agree with you on the car being indestructable. my dad came out the the track yesterday to drive a 8th scale for the 1st time (he used to race only electric about 4 years ago) after watchin me wheel it arround a few laps he wanted a stab at it. The track we were at had just been extended so on the back stright the barrier for the track started 1/4th the way down the stright. well lets just say my dad ran head on with the end of the barrier wide open! the car flipped a few time and kept on going. Last night i was going to rebuild my shocks when i noticed i couldnt get my wrench in the lower screw. looked at it more and the screw head was smashed in from the hit with the barrier and nothing on the car was broken!
__________________
Rob Jensen
Thanks to the following companies for their support in 2017: Team Associated, Maclan, Fierce R/C Solutions
micrors4guy is offline   Reply With Quote
Old 12-05-2006, 02:35 PM   #987
Tech Fanatic
 
sport10's Avatar
 
Join Date: Dec 2005
Location: Pensacola, FL
Posts: 964
Default

Scuba Steve,

You could try running the rubber gromments that come with the servos on the throttle. This should help absorb some of the flexing of the chassis on punshing blows. Might make the throttle servo last longer.
__________________
Hot Bodies VE8 w/ RX8-1900 combo
Losi XXX-SCT CRC conversion MMP/hacker 13.5
Associated B44
Associated B6
Durango DESC410V2 Pro
sport10 is offline   Reply With Quote
Old 12-05-2006, 03:33 PM   #988
Tech Master
 
Mike Dana's Avatar
 
Join Date: Nov 2001
Posts: 1,508
Trader Rating: 6 (100%+)
Default

To add to the flexible radio tray/servo failure discussion.....

Please note that IF flex was a problem you should some of the following:

elongated servo mounting holes on the servo mounting ears AND/OR the radio tray,

the servo mounting screws should be loosening seemingly "on there own"

you should see shiny, polished spots on the radio tray under the servo mounting ears.

I think it's rather unrealistic to think that the servo case (small, effective load bearing box section after all) is absorbing the flexural load without the case to tray interface showing evidence of movement.

Regardless, bottoming a chassis out (pancaking a chassis, etc) would not be "flexing" the chassis as is theorized here as the failure mechanism of the servo. Bottoming out of the chassis would be the most efficient method of transmitting shock to ALL shock critical devices (servoís, receivers, glow plugs, etc.). Now, end-over-end cartwheeling would much more likely throw a chassis in an out of maximum flex.

Personally, I'm leaning toward the incorrect linkage spring/ball cup-coil bind issue as the cause of the failures.

Mike Dana is offline   Reply With Quote
Old 12-05-2006, 03:37 PM   #989
Tech Champion
 
R40Victim's Avatar
 
Join Date: Jan 2005
Location: N.W. FL___L.A.___Lower Alabama
Posts: 7,822
Trader Rating: 1 (100%+)
Default

Interesting info guys!...keep it comming. My most recent servo(a Z590) has servived for several runs(several more this weekend at a friend's track). Every time I install a new thottle servo, I use the rubber gromets, and I only tighten the mounting screws just enough to keep it from moving. That way, if it does flex, it's less likely to tweak the servo. It also reduces the intense vibration from the motor being transmitted to it.

Sorry to hear you blew two $110 servos. I was planning on installing a 9000T for steering soon. My theory is that it must be pretty durable to handle 320 oz of torque. I don't plan on running anything more expensive than a Z590 on my throttle until we figure out what's going on...
R40Victim is offline   Reply With Quote
Old 12-05-2006, 05:07 PM   #990
Tech Master
 
SCUBA STEVE's Avatar
 
Join Date: Aug 2004
Location: Ohio
Posts: 1,836
Trader Rating: 85 (99%+)
Default

Quote:
Originally Posted by Mike Dana
To add to the flexible radio tray/servo failure discussion.....

Please note that IF flex was a problem you should some of the following:

elongated servo mounting holes on the servo mounting ears AND/OR the radio tray,

the servo mounting screws should be loosening seemingly "on there own"

you should see shiny, polished spots on the radio tray under the servo mounting ears.

I think it's rather unrealistic to think that the servo case (small, effective load bearing box section after all) is absorbing the flexural load without the case to tray interface showing evidence of movement.

Regardless, bottoming a chassis out (pancaking a chassis, etc) would not be "flexing" the chassis as is theorized here as the failure mechanism of the servo. Bottoming out of the chassis would be the most efficient method of transmitting shock to ALL shock critical devices (servoís, receivers, glow plugs, etc.). Now, end-over-end cartwheeling would much more likely throw a chassis in an out of maximum flex.

Personally, I'm leaning toward the incorrect linkage spring/ball cup-coil bind issue as the cause of the failures.


Mike, You are correct in that I did pancake it pretty Bad!!.... and that would not cause it to flex but instead rattle all the electronics...and that's what did the servo in.
But, Believe all of us when we say the chassis does flex alot! and so does the radio tray.
Also I guarantee my linkage is perfect.


****One thing I forgot to tell you all is that at one point my chassis flexed so bad that my center diff brace hit my slide on the carb and twisted the carb in the block and tweaked the carb itself! Luckily I fixed that.****

By the way the track I run on has crazy jumps to the point that they are going to change it because it has become a safety issue for the marshals so that's why I have been noticing all the flex lately and bottomed so hard!

Thanks to all ....I'm going to put the rubber gromments on like alot of you guys are saying.... I appreciate the info!
SCUBA STEVE is offline   Reply With Quote
Reply

Similar Threads
Thread Thread Starter Forum Replies Last Post
Losi 8ight Clutch building Cvdiver Nitro Off-Road 3 05-21-2008 04:47 AM
Team Losi 8ight Buggy with Brushless Setup RcOneNitro R/C Items: For Sale/Trade 9 04-20-2008 06:04 PM
losi 8ight-t package f/t for brushless lipo setup ColeT R/C Items: For Sale/Trade 6 03-02-2008 11:17 AM
Losi 8ight-t setup F/s ColeT R/C Items: For Sale/Trade 15 02-11-2008 08:51 PM
OS .21 V-spec Cluth Setup on Losi 8ight? RcOneNitro Nitro Off-Road 6 09-03-2007 01:07 AM



Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are Off



All times are GMT -7. It is currently 09:50 PM.


Powered By: vBulletin v3.9.2.1
Privacy Policy | Terms of Use | Advertise Content © 2001-2011 RCTech.net