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  1. #1
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    Looking for Answers from the Pros here...

    I recently received my ERBE, charger, power supply, and batteries. I have been reading for a while and found lots of useful information. I am hoping for some clarification on a few things though.

    1st-I am running two 2s 40c 5000mah batteries and I believe that keeping stock gearing is safe. The speed is close to that of my Revo 3.3 and the amount of torque is perfect. I'm only asking because the fan on my ESC is kicking on after 10-15 minutes of light bashing, but motor is still touchable and temped at ~ 120 f. at hottest.

    2nd-I have yet to find a clear answer on lipos. Is 3-7 days considered storing or is it safe to leave the lipos fully charged for this amount of time (recharge after Saturday bash and leave until next Saturday)? And is a fridge really necessary? Do the lipos need to be balance charged EVERY time?

    3rd-Is the LVC on stock ESC really unreliable? I have set it at 3.5v per cell using Castle Link and I would like to rely on it. I can time my runs, but I do something different every time I drive. Creeping along mountain trails and light crawling barely drain the batteries, while speed runs and full blown bashing are different still.

    4th-What is the exact part used to bridge the shocks and make the mod to stiffen the rear end? I have the rods, but not sure what that pre-made piece is that all the pictures show.

    5th-What is the punch control used for in Castle Link software? Is this to limit the amount of initial power from motor on start? Isn't that what the throttle curve is for?

    I have a MERV, Revo 3.3, Classic Maxx, and others so I'm familiar with lots of stuff, but always looking to learn more. Please chime in with any advice, suggestions or ideas.

    Thanks, and sorry about the long read. Trying to get everything out in one go rather than start 8 different threads.
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  2. #2
    RC Turnbuckle Jr.
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    Stock gearing is safe, though the system is capable of much more wiht 4s lipo- anything upto about 24/68 is fine, though 20-22/65 is plenty for most. Strange that the esc fan is kicking in, though it does depend on driving style, terrain & ambient temps etc.

    There is no definite answer about storage time for chsrged lipos, but as a guideline 7 days is okay- any longer and they should be stored at 50% charge ( ~3.7v ) really to avoid the anode & cathode corroding. They dont really need to be stored in a frdige, though a cool location is better really rather than a hot area/ direct sunlight. It is best practice to balance charge everytime yes- the best quality cells shouldn't get out of balance so it wont add anything much to the charge time, but lesser or unmatched cells will drift slightly over time, so balance charging is recommended ( it's just a good habit to get into ).

    The LVC is quite reliable but it is also best practice not to rely on it 100%, one must learn to master 'The Force'; when the lipos are becoming discharged near the end of the run the voltage drops off quite rapidly- you will notice this quite easily as the power, speed and punch disappears when you accelerate or mash the throttle. At this point you should stop running the truck regardless of whether the LVC has kicked in or not ( this is why I like the stand-alone buzzer type LVCs as they will buzz when the voltage begins to dip- the sample rate on the built-in LVC isnt always high enough to catch momentary dips in voltage below the LVC threshold ).

    You can either use the sway-bar mount that goes on the shock tower, as sold by TeknoRC and a few others, or you can make it yourself very easily from a small scrap of aluminium ( a T shaped piece ). It's just a simple case of bolting it in place with the shock tower screws so that you have an extra location for the screw which hold the turnbuckle in place- if you;ve seen the pictures you'll have a good idea of what to make.

    Punch control and throttle curve can both be used to achieve a similar effect, though throttle curve can affect the acceleration rate all through the throttle travel, where as punch control limits acceleration essentially whenever you mash the throttle- good for standstarts to prevent/ reduce wheelies and back flips. The torque control feature works like punch control, but is much more effective and doesn't leave the throttle feeling so unresponsive- you just have to hope the later firmware versions which have it don't leave you with the low throttle glitch ( v1.24 is the last 100% bug-free firmware, later versions than that may or may-not cause you issues.. ).

    If you want more advice, tips or hints etc:

    Erevo 101:
    EREVO FAQ

    Lipo, LVC, Brushless & Battery charger/charging guides & purchasing links:
    TUTORIALS

    Refer to this to setup the Mamba Monster ( MMM ) esc for maximum performance:
    CASTLE LINK GUIDE

    Refer to this to find parts, upgrades, batts & chargers etc:
    USEFUL LINKS


    And direct from CastleCreations ( the esc manufacturers ):
    MMM FAQ

    Driver's ED Manual

    LED warning light meanings

    Enjoy
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  3. #3
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    Anything longer than 48 hrs (max) should be considered storage. Hopefully ur batteries havent showed any signs of internal resistance rise yet... The only place i have seen any information about this was on spc website.

    Let the LCV tell u when to stop is fine. With cars it is much harder to time the runs. You are right.
    Last edited by anr2442; 08-01-2011 at 12:48 PM.

  4. #4
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    Thanks for the replies.

    AOD I have read most of those links and still have questions. The tutorials link mentions hot ESC and cool motor = over geared. What does that mean? And also you say with different gearing it is capable of more with 4s. Can you elaborate on this? Are you saying that the included 'optional' gearing is better? I guess I'm not clear on this. The numbers 18/65 (stock ERBE) means 18 tooth on metal pinion, and 65 tooth on the plastic gear right? The more teeth on the pinion basically means it's bigger right? That means it turns the plastic gear more per turn which increases speed? Is there a link to a complete guide on gearing? Thanks again.


    anr2442 - 48 hrs max huh? Guess my storage mode on the charger will be getting quite a bit of use then. I have only had the batteries for 5 days and they have yet to sit even 48 hrs charged fully. My charger is currently discharging 4 of my 8 lipos to the recommended 3.85v. Thanks for the input.

    Anything else you guys want to throw at me please do. Always thankful for knowledge.
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  5. #5
    RC Turnbuckle Jr. 87 GN's Avatar
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    Quote Originally Posted by anr2442 View Post
    Anything longer than 48 hrs (max) should be considered storage. Hopefully ur batteries havent showed any signs of internal resistance rise yet... The only place i have seen any information about this was on spc website.

    Let the LCV tell u when to stop is fine. With cars it is much harder to time the runs. You are right.
    I would still time the runs, I would not rely solely on the ESC LVC. If you have one cell that is a bit lower then the rest, you could take that cell to low. JMO

    Also Boo unless you have to I would not use the discharge on your charger. Every cycle of the batts is one more step towards them dying. Run your batts & if it will be several days to the next run charge them up to storage.

    In time you will be able to tell the batts are about done. You will not have the same punch as when you started with a full pack(s).
    Last edited by 87 GN; 08-01-2011 at 03:45 PM.
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  6. #6
    RC Turnbuckle Jr.
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    Quote Originally Posted by Booeenie View Post
    Thanks for the replies.

    AOD I have read most of those links and still have questions. The tutorials link mentions hot ESC and cool motor = over geared. What does that mean?
    Overgeared means overgeared- you are physically asking the motor to work too hard, which causes it to draw lots of current from the batts via the esc. The batts and esc will heat up faster/ more due to this increased current draw, but the motor itself often does not, or takes longer to heat up- depends on the quality quite often as low quality/ high kv motors tend to run hot regardless of gearing. Takes a bit of experimenting sometimes to get a good balance of temps without anything running too hot.

    And also you say with different gearing it is capable of more with 4s. Can you elaborate on this? Are you saying that the included 'optional' gearing is better? I guess I'm not clear on this.
    It means the stock gearing is feeble , and intended mainly for use with nimh batteries which cannot supply enough to allow the motor to pull taller gearing ( for higher speeds ). A BL system is a torque monster, feed it decent batteries and it will happily pull pretty tall gearing usually. 18/65 is good for only ~30mph either with 14nimhs of 4s lipo- use 4s lipo and you can easily gear up to around ~20-22/65 for 40mph topspeed, maybe a little higher depending on how the temps do & battery quality.

    The numbers 18/65 (stock ERBE) means 18 tooth on metal pinion, and 65 tooth on the plastic gear right? The more teeth on the pinion basically means it's bigger right?
    Assuming you use the same ( correct ) pitch gears ( MOD0.8 / 32pitch ) , then more teeth = bigger gear to fit them all in- pretty simple concept really.

    That means it turns the plastic gear more per turn which increases speed? Is there a link to a complete guide on gearing? Thanks again.
    Gearing up = larger pinion and/or smaller spur = higher top speed but slower acceleration & less torque.

    Gearing down = smaller pinion and/or larger spur = lower top speed but faster acceleration & more torque.

    That's as complete of a guide to gearing as you will get- traxxas do provide a basic gearing chart on their site, but the numbers seem to be a little off compared to the more useful gearing calculator BrianG provides:



    http://scriptasylum.com/rc_speed/top_speed.html

    Enter the info by selecting it from the drop-down menus ( you can download the calculator to use offline too ), then play with the variables such as gearing and battery voltage/ cell count- it is best to use 3.7v as the cell voltage of lipos for the most accurate results. Here are a couple worked examples:

    Differential Ratio: 2.8461538461538463
    Transmission Ratio: 1.8333333333333333
    Other Ratio: 1
    Spur Tooth Count: 65
    Pinion Tooth Count: 18
    Total Voltage: 14.80
    Motor KV: 2200
    Tire Diameter (inches): 5.9
    Tire Ballooning (inches): 0
    Motor Current Draw: 0
    Motor Coil Resistance: 0.006
    Spur/Pinion Ratio: 3.61 : 1
    Total Ratio: 18.84259 : 1
    Tire Circumference (inches): 18.54 inches (470.8 mm)
    Rollout: 0.98:1
    Total Motor Speed: 32560 RPM
    Vehicle Speed: 30.33 mph (48.72 km/h)
    Effective KV Value: 2200
    KT constant: 0.61 oz-in/A
    30mph with 4s lipo and stock gearing.

    Differential Ratio: 2.8461538461538463
    Transmission Ratio: 1.8333333333333333
    Other Ratio: 1
    Spur Tooth Count: 65
    Pinion Tooth Count: 22
    Total Voltage: 14.80
    Motor KV: 2200
    Tire Diameter (inches): 5.9
    Tire Ballooning (inches): 0
    Motor Current Draw: 0
    Motor Coil Resistance: 0.006
    Spur/Pinion Ratio: 2.95 : 1
    Total Ratio: 15.41667 : 1
    Tire Circumference (inches): 18.54 inches (470.8 mm)
    Rollout: 1.20:1
    Total Motor Speed: 32560 RPM
    Vehicle Speed: 37.07 mph (59.55 km/h)
    Effective KV Value: 2200
    KT constant: 0.61 oz-in/A
    37mph with 4s lipo with 22/65 gearing. This ofcourse doesn't factor in such things as wheel spin or tire ballooning which can alter the topspeed quite a bit by robbing speed or increasing the overall gear ratio ( larger tires = higher gearing ).

    anr2442 - 48 hrs max huh? Guess my storage mode on the charger will be getting quite a bit of use then. I have only had the batteries for 5 days and they have yet to sit even 48 hrs charged fully. My charger is currently discharging 4 of my 8 lipos to the recommended 3.85v. Thanks for the input.

    Anything else you guys want to throw at me please do. Always thankful for knowledge.
    48 hours seems somewhat overly cautious, but it doesn't take long to fully charge a lipo from storage voltage I suppose.
    Last edited by ArmyofDarkness; 08-01-2011 at 03:46 PM.
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  7. #7
    Marshal ksb51rl's Avatar
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    Quote Originally Posted by anr2442 View Post
    Anything longer than 48 hrs (max) should be considered storage. Hopefully ur batteries havent showed any signs of internal resistance rise yet... The only place i have seen any information about this was on spc website.

    Let the LCV tell u when to stop is fine. With cars it is much harder to time the runs. You are right.
    Here's another reference. It does not mention 48 hours, but does mention 2 days.
    RC Lipo Testing.

    Quote Originally Posted by ArmyofDarkness View Post
    ...48 hours seems somewhat overly cautious, but it doesn't take long to fully charge a lipo from storage voltage I suppose.
    This was not a number thrown out randomly, nor is it overly cautious. Those who buy cheap batteries won't care about the damage being done to their packs and those who buy cheap chargers won't want believe this is the case because it's such a pain in the neck to discharge packs at 1-amp. Either way, VERY few places will be as honest about the product as the sites referred to above.
    Last edited by ksb51rl; 08-01-2011 at 11:15 PM.
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  8. #8
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    Thanks again AOD. I was making the gearing ratios far to complicated.

    EDIT*-I have that gearing graph from the box, but what you posted compared to mine is way off. Have they just changed stock gearing? I started at 18/65, and the optional was a 54 tooth spur.

    I will time my runs, and pay close attention to throttle response on the car and avoid relying on LVC.

    Batteries are not cheap, and idea of being able to use them hundreds of times was a big seller for me. That's exactly why I ask questions. I appreciate the link also ksb51rl.

    According to that link 3.85v is too high for storage, but that is what my professional charger is set to charge/discharge to in order for storage. Does this mean I need to do it all manually? After all my reading I was pretty sure that was the correct voltage. They even came to me boxed at 3.81v.
    Last edited by Booeenie; 08-02-2011 at 10:26 AM.
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  9. #9
    RC Turnbuckle Jr.
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    ~3.8v per cell should be fine, I can't imagine 0.05v will make too much odds for 2 days or a week of storage- you can always monitor and stop the charge once the cells are upto about ~3.7v if it concerns you.
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  10. #10
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    Quote Originally Posted by ksb51rl View Post
    Here's another reference. It does not mention 48 hours, but does mention 2 days.
    RC Lipo Testing.

    This was not a number thrown out randomly, nor is it overly cautious. Those who buy cheap batteries won't care about the damage being done to their packs and those who buy cheap chargers won't want believe this is the case because it's such a pain in the neck to discharge packs at 1-amp. Either way, VERY few places will be as honest about the product as the sites referred to above.
    That link mentions setting the LVC to 3.4v minimum to stay within the 80% DOD. I think this is HIGHLY dependent on the usage.

    In cars, average current draw is generally rather low (typically ~15A in a reasonably-geared 1/8 scale MT), but peaks as high as 10X the average value. During those current peaks, voltage does sag even when the pack is fresh. If the LVC is set to 3.4v, the ESC may trigger a false LVC during high current peaks (especially for those geared high).

    However, in airplanes, current is much more constant. The average current draw is higher than a car's, but the peak currents are much lower than a car. So setting a higher LVC makes much more sense since you don't need to worry as much about false LVCs from huge differentials in current (and therefore voltage).

    In helis, I think it depends on what you are doing. If just doing light flying/hovering, the power usage profile more closely matches that of an airplane - more consistent current draw. But if you are doing those low-hover-to-100-foot-bursts in 2 seconds, that more closely matches the power usage profile cars see (actually worse because the average current is higher than a car's, the peak currents are the same or more than a car's, and those peaks last longer).

    Personally, I have my LVC set to 3.2v/cell on my Castle ESCs. When I pull the batteries off right away and hook them up to the charger, they have already "drifted" back up to at least 3.4v/cell. If left for ~10 minutes unloaded, they drift to around 3.5v. However, I do use pack temperature as a guide. Internal resistance increases towards the end of the cycle. If your pack is really warm, then you must have run too far into the end. If the pack is ~15F above ambient temps, then that tells me that I am far enough away from end of the cycle since resistance hasn't started climbing yet.
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  11. #11
    RC Turnbuckle Jr. brushlessman's Avatar
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    lol i do none of the above and my lipos are just fine. run them down to lvc and let them sit for a week. charge them fully and let the sit for a few weeks. they are fine. Just keep them balanced and they will be fine. Lol but thats my way of being lazy

  12. #12
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    2c: This is an enthusiast forum, and as such there's a lot of talk about best practices. That said, quality components can better tolerate mistreatment, so it's not surprising to see folks getting decent performance without all the rigorous discipline. This is especially true if they aren't professional racers that need and can notice every last ounce of performance.

    Such recommendations and best practices are not absolute requirements, but all else being equal it's probably best to be on the safe side. =)

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