Is it possible??

[XXChAoTiCXX]

Hey everyone, I am am trying to get my Hyper 7 tuned up, and I have noticed that when running it, as the Rx battery gets weak, my servos start to show the lack of power. My steering servo is a Hitec MG645, and it performs well, for way longer than the stock OFNA servo that controls my throttle/brake linkage. It seems that as I run the car, eventually the throttle servo gets too weak to return the carb to it's idle position. Is this a problem with my servo? Or the way I have my linkage set up?

Here is what I run:

Hyper 7 PBS w/ hyper .21 8 port, pullstart removed
Hitec MG645 Steering servo
Stock OFNA Throttle servo
Stock AM Receiver and transmitter
Duratrax 6.0V 1100Mah 5 cell NimH Rx battery

I just can't believe that it may be possible that the stock servos are so worthless that they don't even function properly when fed w/ 6 volts.
Either way, I have another MG645 on order, so I hope it will remedy my problems, but I would like some expert advice.
As always, thanks in advance for the help....


-XXChAoTiCXX

[RcTire]

how long do you usually run the car before it starts to lose power?

[XXChAoTiCXX]

Between 30 mins. to 45 mins. It is just really frustrating b/c I can't get good tuning temps if my idle is always running so high....

[robriguez]

If the servos work fine everytime you connect a freshly charged battery the problem is most likely NOT the servos. All electronics will eventually drain a battery and as that happens the amount of voltage available drops off. NiMH batts hold their charge longer than NiCD but they will eventually drop off as well. One of the things you can do is to test the voltage when this problem starts to happen:

1) If it is below 4.8v then the battery if defintily too week to continue running. Either your battery is starting to no longer funtion properly (and should be replaced) or your servos are just pulling too much voltage. (In which case it might be a good idea to get a second or third batt to keep on hand and swap it out when the first dies.
2) If the voltage is still 6.0v steady then the problem is most likely one or both of the servos themselves. They may be overheating cauing them to not work properly.

Finally, it shouldnt take 45 min to get a good tune on your engine. Within 2-3 min of run time (4-5 min of idle) your engine should be completely up to temp. If your engine is not heating up quickly enough because of the outside temp (winter time) then you may want to cover the engine head with some tin foil or some people use a peice of posterboard paper and zip tie it on the head. Its just to minimize the airflow to the engine so it has a chance to get up to temp properly.

[Mondo]

robriguez has spoken words of wisdom - it's taking too long to tune that engine. Check for fuel line/carb leaks too..

Back to the "issue" at hand, 30-45 minutes is a repsectable runtime on a 6V 1100mAh RX pack.
In my buggy I use a Hitec HS645 steering servo, a HS625 for throttle/brake duty, run an AMB Personal Transponder an a failsafe unit.
All my packs are 6.0V 1100mAh NiMh units and on practise day I get about 4 tanks during track use before suffering the symptoms of the RX pack running low - so we're talking 25 minutes of runtime max.

On raceday I do two 5 minute heats on my buggy before swapping to a freshly charged RX pack for the next two heats. I also use a freshly charged RX pack for the 15 minute Main, so in one day of 35-45 minutes of track time on raceday I use 3 RX packs in my buggy. It's overkill, but in a race environment only the paranoid survive!

[Plaidfish]

damn guys I must have super Rx packs...I read these threads about 1 hr is good, but I can remember having over 1/2 gallon on one pack....I notice some loss of performance but nothing I'm overly concerned with....but when they ydo drop off they just die.....Part of these times I'm sure is from using a really good charger but the differences I'm hearing just seem unreal to me.....do you guys shut the pack off when you go to your pit to fix / tune / tweak stuff????


during races (If I can ever get to one again) I don't risk running out of battery, I keep 3 on-hand and my charger goin the whole day.....like mondo said in a race environment......

[niggle]

I'd go with the faster 625MG for throttle/brake, it has more than enough torque for this task.

Also try a longer, softer spring on the throttle rod. If the carb slide moves smoothly in the carb body then you don't need a strong spring to keep it closed and the servo has less tension to overcome when you apply the brakes. The spring from a rectractable ballpoint pen is ideal.

At the end of the day it might just be the trim on your Tx and the preload on your existing throttle rod spring that is failing to keep the throttle shut. With the original spring and servo on my buggy it was a very fine line between keeping the throttle shut at idle and having little enough tension so that the brakes could be applied fully.

Maybe your could borrow a newer/bigger Rx pack from a friend to see if this improves the situation? 1400mAH Rx packs are available now from several vendors.

[Plaidfish]

you can kill a pack real quick if your EPAs (End Point Adjustment) aren't set....everytime you go WOT the servo will keep trying to go further than it needs to...same thing w/ braking and steering....every time one of your servos hits the physical limit of travel that's where you want the EPA from the Radio to say enough......

[evan811]

Plaid, What id my radio doesent allow me to set EPS's? its only the stock radio....

[Mondo]

Good catch there guys! I clean forgot about the EPAs! Those can be a killer.
Niggle, great advice on the throttle spring too! You're gonna have me running around the house collecting ball point pens before the next race meeting in spring! LOL!

Evan811, if your TX doesn't support EPAs then it's time for an upgrade. A decent entry level programmable FM TX/RX combo like the Hitec Agressor isn't too expensive. I use one of these for my Micros (as I use a KO MARS-R for racdeday) and the Agressor is good value for money.

[Plaidfish]

yep, what mondo said......look on E-bay and you'll find JR XS3 sets for real cheap.....I've seen em go as cheap as 50 bucks (rare) for a new one.....I'd recommend the Futaba 3pm......should be able to get one w/ no servos for about 110 new.....

[evan811]

yeah, a radio shoudl be my next upgrade, I already have spektrum servos, there awesome, IMO. Should I get a new rx too? Its the stock OFNA one....

[XXChAoTiCXX]

I love this place, you guys are a wealth of info!! I especially appreciate niggles point about the spring, that was somethng that had caught my attention previously. Unfortunately, I already ordered a 645MG for my throttle, so that will have to do. My next investment will be a radio with EPA capability. Can someone recommend a good radio system w/ receiver for under $200 new?? I don't want used radio equipment.
Thanks again all!!

[robriguez]

while its possible to get an hour of constant run time out of an 1100Mah bat I wouldnt trust it that long. Once the voltage drops below 4v you start to lose range and steering responce. Depending on how your racing or bashing that could be BIG trouble. Get out of range and you could have a run away on your hands. If you dont have a voltage meter (or even if you dona nd dont know how to use it) you might want to look inot getting a voltwatch.

http://www2.towerhobbies.com/cgi-bin...?&I=LXHDJ2&P=7

Once you see the lights getting into the yellow area time for a fresh pack or a recharge.

[Plaidfish]

What makes it even more outrageous is I run 2 digital servos too....I only run at the track and it's pretty much closed in...also spektrum....built in failsafe.....it gets quirky and I just change it but I get a good hour of run time on one pack and at least 30 mins on the other 2.....my hump packs on the truggy all get about 45 mins each......that's what I get out of em all the time.....all XS Power packs and a racers edge one....