CRT.5 build - would opinions on my setup choices

[VintageMA]

Originally Posted by dway

I think regular lipos would be a better choice. You are only going to have enough room to run a 4s1p pack at 13.2v 2300mah or a 2S2P pack at 6.6v 4600mah. I don't think either one is a very good option.

dway - Comments like this without any technical support on the statement don't carry much weight around here. Do you have any technical reasoning behind your comments?

I also have 2 of the MaxAmps 3S 5000mAh packs myself, but I actually opted to go with the A123 batteries for several reasons:
-Weight - the weight of a 4S A123 pack will balance out nicely against a 8L and ESC mounted on the other side of the car.
-Amp draw - this buggy weighs like 5lbs wet - the highest peak current draw on my BL LST2 with a LMT 1950/7 and 6S in a 14-15lb truck is 85Amps. So I have no concern with there being a current limiting factor.
-Motor - at 3019kv the 4S A123 puts the 8L right in its sweet spot.
-Safety - I've had 4 2S 3700mAh lipo packs (the Firefox ones from FDM) balloon and swell on me just storing them at ~50-60% charge. This has me very concerned as I live in an apartment and don't have a garage. Even though I store the cells in a metal lock-box - I get worried about fire now. If the A123 cells prove them to me on this installation I may consider getting more of them.

Re: the volt drop on the cells - check out the pdf in my first posting. @25*C w a 30A load the cells show a running voltage of ~2.8v. Just like jhautz - this is why I will run 4S A123 instead of 3S Lipo.

JHAUTZ - I'll post some pics on this thread as I am building. A few questions for you if you've thought out some build issues.
1 - What are you going to be using for the battery mount? This is the one place my customization and craftmanship skills always struggle.
2 - Do you think I should get a UBEC as well for the 4S A123? I was going to try the BEC in the MM - but I know I've read a lot that the MM BEC gets hot even on 3S LiPo.

[Mailman]

Originally Posted by VintageMA

dway - Comments like this without any technical support on the statement don't carry much weight around here. Do you have any technical reasoning behind your comments?

I think BrianG answered this for me -(I had my user name changed from dway)
There is nothing "technical" about it I was just stating my personal opinion. If you don't mind running a 6.6v battery and getting poor performance but longer run times , or a 2300mah battery and getting better performance but lower run times then go ahead. I can understand wanting to do it for the safety aspect of it, but either your performance or your run time will suffer. The only reason I suggested a lipo was that you get the voltage needed and run time too.

[VintageMA]

Originally Posted by Mailman

I think BrianG answered this for me -(I had my user name changed from dway)
There is nothing "technical" about it I was just stating my personal opinion. If you don't mind running a 6.6v battery and getting poor performance but longer run times , or a 2300mah battery and getting better performance but lower run times then go ahead. I can understand wanting to do it for the safety aspect of it, but either your performance or your run time will suffer. The only reason I suggested a lipo was that you get the voltage needed and run time too.

Trust me - I am a big LiPo fan - I've probably spent $2K on LiPos alone in the past 2 years. But after having $500 worth of (well cared for and balanced regularly) balloon on me - it's time to try something a little different and see how it works. I went with the 4S config on the A123s because that's the closest to 3S Lipo - so I obviously want the performance.

We'll see - maybe I'll end up using the 3S 5KmAh MaxAmps pack in the long run. I plan to setup with a battery mount that will support both.

And if I set the MM for a 9Volt cutoff I will be able to interchange either the A123s or the LiPo w/o making any changes to the cutoff on the ESC. For 3S lipo it will be right on the mark at 3v/cell and for the A123 it will be just a touch higher than the recommended 2V @ 2.25v/cell.

Give it a month to have everything shipped and we'll see.

cemetery gates - what gearing are you using with the 10L and what brand is the motor? I've noticed the Feiago motors will tend to pull higher power spikes than the LMT/Neu's with the stronger magnets.

Originally Posted by VintageMA

cemetery gates - what gearing are you using with the 10L and what brand is the motor? I've noticed the Feiago motors will tend to pull higher power spikes than the LMT/Neu's with the stronger magnets.

It is a feigao 10L geared 20/46 (tops out at 39, radared). In my revo with a neu 1515 1y on 4s and I get many 120+ amp spikes. In your case you are running 6s with a lower kv motor so, you will pull less amps...

Bye

[VintageMA]

To move back on track with my original post - the parts are coming in.

Got the Hacker B50 8L today - feels like a nice solid motor. Not a Feiago but not quite a LMT/Neu either.

Got the motor mount and pinions in from Mike - very quick shipping as always!

Got the A123 batteries and charger - the A123s seems like some solid cells. Small issue with the charger though - it let it's smoke out ;) Hooked it up to me DC power supply and the lights were wigging out on the charger. Played around with it for a bit and when I went to hook it up the second time and tried tohook up a battery for charging a puff of smoke came out of the front of the charger. A123Racing has alrady agreed to repair it at no charge if I send it in, but considering it is dead out of the box and am trying to see if Horizon Hobby will do an RMA first before I send it in to A123.

Guess I'll be starting the build and testing this out with the 3S 5k mAh lipos anyway.

Now all I need is the buggy - FedEx Ground coming from CA seems to be taking a while - was hoping to have it for the long weekend.

[VintageMA]

Good support from Horizon Hobby - they are arranging a RMA for the charger.

Originally Posted by VintageMA

-Amp draw - this buggy weighs like 5lbs wet - the highest peak current draw on my BL LST2 with a LMT 1950/7 and 6S in a 14-15lb truck is 85Amps. So I have no concern with there being a current limiting factor.

I have a crt.5 w/ext chassis that runs a 10L(2458 kv) off of 3s(weighs about 5lbs). I have seen 90+ amp spikes out of this so, you might be suprised at how many amps an 8L can pull, just to let you know...

Bye

[jhautz]

Originally Posted by VintageMA

JHAUTZ - I'll post some pics on this thread as I am building. A few questions for you if you've thought out some build issues.
1 - What are you going to be using for the battery mount? This is the one place my customization and craftmanship skills always struggle.
2 - Do you think I should get a UBEC as well for the 4S A123? I was going to try the BEC in the MM - but I know I've read a lot that the MM BEC gets hot even on 3S LiPo.

I typically just use some velocro on the chassis and the pack, then strap it down with a gorilla maxx strap. I havent had any issues with it yet. If it were lipo I would make some sort of box out of Carbon Fiber angle stock or aluminum or plastic to protect the cells more.

Yes, use a UBEC for sure. A cheapo will due just fine for this small truck. Just get a $15 one from one of the flyer websites.

Sorry for the delayed response. I didnt catch that you asked a question at the bottom of the post.

Originally Posted by VintageMA

jhautz - What servo are you going to use. I picked up the HiTec HS-5245MG, but I've seen some threads on here about people overheating them with too large tires.

I've always had very good luck with HiTec digital servos, and I am planning on making the jump to 75MHz FM to DSM2 when the Spectrum DX3R radio comes out this fall - so I wanted something solid that I could run at a higher frame rate.

I'm using the same one. Just ordered it a few days ago. Should be here soon. On the plus side the CRT.5 showed up yesterday. (grin)

[VintageMA]

The buggy should hopefully arrive tomorrow for the weekend.

I guess I am still missing the UBEC - can you send a link to one?

Any idea what you are going to use for the diff fluid? I've been reading 3K f/3K c/ 1K r is a popular starting point - but I am wondering if it would be better to go go with the standard 3/7/1 used for buggies - I'm never sure where to start with that as I mostly just bash and don't race.

[jhautz]

Just look around. there are alot of places that sell em. Mike has a higher end one in his store.

[VintageMA]

Just got the CRt.5 in today - WOOHOO!!

Thought this was cool. I ordered it from A Main Hobbies and it came with a 2nd set of wheels :)

Let the fun begin.