ASK Cub Reporter, 01.03.2013, You Have the Questions, I Have a Headache

Hello BSRC!

Got a Helion Dominus 10TR question? Picked mine up at Hobbytown and the tech guy said a slipper clutch would be good idea. So got home out slipper clutch in and have a binding noise coming from the diff area ever since.Took it back to hobbytown they took it apart and couldnt find problem..The slipper install was a nightmare in general…but i love the thing it jumps like a beast….But i cant run it with that noise drives me nuts…….HELP PLEASE!

Chris R.

Cubby– Hey ya Chris and thanks for the question via our Facebook page. Hit Brian up for some free stickers, tell him I sent ya and to too hook ya up.

This is one of those problems that is quick to track down in person, but difficult to do via the Internet. But if I had your truggy in my hand right now…

Here are my upfront guesses for where your noise is coming from- 1. from your new slipper/spur rubbing on something, 2. motor pinion/spur mesh (a slightly chewed up spur), or 3. you have a diff going bad.

First step is simply listening, listening to see if you can hear the actual area the noise is coming from. Sometimes this can be deceiving, but take the body off, put your truggy on a work-stand with the wheels off the table, then lightly hit the throttle and take a close listen. Hopefully this will give you a specific area that the noise is coming from, if you still can’t tell where it’s coming from…

Because this noise started after your slipper install I’d take a close look at the slipper/spur and see if it is rubbing anywhere. Look for scuff marks on the slipper itself. Also, look for small bumps or excessive wear on the teeth of the spur where it mates with the motor pinion. You would be amazed how much noise a slightly chewed up spur gear can make. A small bit of dirt (or small chunk of plastic) in the teeth of the spur can make one heck of a racket as well.

If you don’t see any scuff marks on the slipper and the spur looks good I would then loosen up the motor pinion/truck spur gear mesh, make sure the two gears are no longer touching. Lightly hit the throttle again and listen. Most likely you’ll hear no noise, as just the motor and pinion are spinning. Hear no noise from just the motor? Then we go to the next step->

Next, spin the spur with your finger and listen. Btw- the spur should spin quite freely without resistance. Is the sound still there? If it is- it might be the rear diff (or ring/pinion bevel gear inside the diff case). If you spin the spur and there is no noise, then the noise is being made when the motor pinion and spur gear are mated together.

If you are still hearing the noise when spinning the spur I would remove the rear driveshafts from the rear differential out-drives. I would then spin the spur again and see if the noise is still there. If the noise is, then you’ve narrowed it down to something inside the diff case. If the sound is gone, then it has to do with the wheels or driveshafts.

I could go on with the process here, but really it is a matter of taking some time and doing a process of elimination. This is a hobby, by owning a truck you are volunteering a certain amount of time to taking care of it. Tracking down a mystery noise is just part of the “fun” of getting to know your truck better and making sure it is in tip-top working condition. Good luck and be sure to shoot us an email telling us what it turned out to be.

I liked the review of the passport duo charger… I have a couple questions… After reading the article (which was nicely done) I wanted to ask you… can you charge any lipo 2cell battery at the 10.0 amp charge rate… if so, what benefits are there to charging at the factory default rate of 2.0. Also, I see you mentioned that charging at the balanced setting could take forever… I was told to always charge at balanced…. are you saying that you only charge at balanced to get the 2 cells back inline and while at the track you use fast charge all the time?

I purchased this charger off your review of it (thanks for the help) I was going to purchase the new Trax power charger with the matching power supply that plugs into it.. I choose this because it was one unit and Big Squid gave a very positive review. I just want to make sure i understand this a little better because i am newer to the sport and wanted to make sure I could charge at a faster rate.

Please let me know if you understand the questions i am asking…

Thank you again and I’m a big fan of Big Squid!!!

Paul P.

Cubby– What’s up Pauly, and thanks for the email. Shoot Brian your snail mail for to get your new T-shirt! Yes! I proclaim yours as “letter of the month”.

To get right down to business here…

Can you charge any 2S Lipo at a 10 amp charge rate? Absolutely not. 2S (7.4v) Lipo batteries come in many different capacities, ie- 1200 mah, 5000 mah, 5400 mah, etc. The capacity of the Lipo, along with its cell design, are used to determine its charge rate. With hobby grade rc Lipo batteries, a relative “safe” charge rate is 1C (just over a 1 hour charge time)- equating to a 1.2 amp charge rate for a 1200 mah pack, a 5 amp rate for a 5000 mah, and a 5.4 amp rate for a 5400. In the last few years the cell designers have changed the internals to be more friendly (read- tolerant) to higher charge rates, today we see Lipo’s with “recommended” charge rates as high as 10C (just over a 6 minute charge time). A 10C charge rate would be 12 amps for a 1200 mah pack, 50 amps for a 5000 mah pack, and 54 amps for a 5400.

At what amp rate should you charge your Lipo? This is typically listed on the pack itself. If you don’t see it printed on the battery hit up the manufactures website, and if you can’t find it there, give them a call. It is important to charge a Lipo battery at the correct rate, don’t charge a pack without knowing it.

Btw, to properly charge a Lipo pack requires two correct settings- 1. the cell count, such as 2S (7.4v) or 3S (11.1), in addition to 2. the amp rate.

Should you balance charge every time? That depends. For example- we have packs around the office that have nearly identical voltage for each individual cell even after dozens of cycles. There is no need to balance a pack that isn’t out of balance.

On the flip side- we’ve got a few packs around here that tend to go out of balance. When we charge those packs we balance them every time. Here’s why- if you quick charge an unbalanced pack one cell will be overcharged (a potentially dangerous condition) while the other cell will be undercharged.

About the Passport balancing slowly- if a pack is minimally out of balance (lets say .02 volt difference between cells) it won’t take that much longer than a “quick” charge, but if it is significantly out of balance (greater than .05) it can take a while. The Passport very slowly discharges the cell (or cells) with higher voltage down to the voltage of the lowest cell to balance them.

Do we fast charge at the track all the time? Yes and no. Yes- if it’s a pack that is nearly balanced and tends to stay that way. And no- if the cells in a pack are significantly out of balance, then we do take the extra time to balance charge.

Should you always balance charge? Sure, if you have the time and/or your batteries need it. But… if you want to save time and your cells stay well balanced, then go for the quick charge.

How much of a difference in cell voltage should necessitate balance charging? Different people will give you different answers on this one, but I balance charge when the difference is .03 volt or more. For instance… if you have a 2S Lipo pack and one cell reads 3.50 volts and the other reads 3.53 volts I would recommend a balance charge. If you have a 3S Lipo and the first cell reads 3.50, the second 3.51, and the third 3.49, I would go with a quick charge if you are looking to save some time.

That’s it for this week gang, shoot me your questions, issues, suggestions, rants, and chest beatings to Cubby at BigSquidRC dot com. Each letter that hits the big time gets free stickers, and if you are cool like Pauly and get “letter of the month” you get a new uber T-shirt.

YOUR Cub Reporter