CRT.5 build - would opinions on my setup choices
 

Placing an order for a CRT.5 for my next project as everyone seems very happy with their conversions and I need something smaller than my LST2 to bash around with.

Config:
-CRT.5 Pro w/ RC-Monster CNC motor mount
-A123 4S1P battery pack (actually 2 - 2S1P packs in series from Horizn Hobby - http://www.horizonhobby.com/Products...odID=AQR400062). I've measured the max burst amp draw from my LST2 at 85Amps, so I figured that 30C/60C 69A/138A for a much lighter truck should be fine)
-Hacker B50 8L (3019kv) motor (at a nominal rating of 13.2 volts for the pack and about 2.8 volts/cell @ 30 amps discharge @ 25*C that puts me in the range of 33812 - 39850 rpm)
-Castle MM esc
-13T and 17T MOD1 pinions (for a caculated speed of about 30 - 40mph)

A123 battery discharge graphs here: http://www.a123systems.com/newsite/p..._FEB2007-1.pdf

Maybe the extended chassis when it comes out? Looks good so far.

This is too wierd!!! I just started getting the stuff together for a CRT.5 myself and that is EXACTLY the same setup I am planning to use. I have the Hacker B50 8L, MM, UBEC and A123 cells here and and the CRT.5 and RCM Motor mount on the way.

You should have a great setup there. I ran the 8L + 4s A123 in my Lightning Stadium 10 for a little while and it ran great on 4s A123. I switched it out for another motor and now the 8L will be going into the CRT.5 I'm thinking it will be a very solid setup, with TONS of power and be able to take some pretty tall gearing with an L can in a tiny little truck like that. May actually need to go down to 3s A123 for the smaller truck. Not really sure till I try it though.

Post some pictures of yours once you get it going. I really want to see the result.

Should be nice.

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.

I'm running 4s1p a123 (built them from dewalt packs) in my Lightning Stadium 10 now with a Lehner 1930/6 and its getting 12-15 minutes of runtime on a charge. Its has real good punch too. Hard running of constant full throttle acceleration slow down for the turn and full throttle acceleration down the straight again in oval racing. Just about as hard as I can run it. They do drop voltage under the load, but thats why I'm running 4s with a 3400kv motor. The a123s take it well. The packs are for sure warm when they come out, but nothing alarming (around 110F)

I have 3 packs and it works perfectly for running almost constantly. I have one pack in the truck running, one pack cooling after the run and one pack charging. I'm using the Xtrema charger and charging at 8 amps so it takes around 18 minutes to charge fully. They just rotate around and it keeps going... and going... and going....

Next time I go out (hopefully friday if the weather is decent this week) I'll try and get an eagletree on a full pack run and post up the real world data.
Heres a link to the thread with pictures of the setup.
http://www.rc-monster.com/tempforum/...read.php?t=853

2300mah just doesn't sound like much, but if you get that kind of run time then I may have to take a closer look at them. I was planning on running a Maxamp 3S 5000mah pack in my crt.5. I gusess the A123 should be able to handle a Plettenberg Maxximum.

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.

It sounds like dway was simply commenting on the realtively low Ah rating of the A123 cells simply for runtime considerations, not total current output.

Either 4s A123 (13.2v nom) or 3s lipo will put the 8L in a decent rpm range, but the 4s A123 will be closer to 40k rpm and might show some high rpm heat depending on how long the motor is run at that speed.

Agreed - but it wasn't clear what angle he was coming from - it's always better to give an explanation than assume other people will know what you mean.

Under load the A123's look like they will drop to a steady 2.8v pretty quickly - which hits it at just under 34000rpm. I am not too concerned that heat will build up before the Vi drops.

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 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.

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

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.

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

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.