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.

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

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.

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)

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.

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

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.

Yeah, mine did too. They have different hub mounting so watch out before you glue the tires on there!

Different hub mounting????

What do you mean? I thought it was like the Losi or AE cross pin style.

One set is the cross-pin style, the other uses the hex hubs...

Yeah - I see that - that's kinda a pain in the butt with different types of wheels - I can't really see using the ones with the cross-pins.

Probably going to put all the nitro stuff that came in the kit up for sale on e-bay (just the muffler piece alone is $50 online) so that'll make up for some of the expense on other parts.

Here's a few pics of what I've done so far. The motor mount isn't great (just some L-arms from Home Depot cut to fit along with velcro tape and velcro straps - but seems to be holding well for some trial runs) - I just don't have the tools or the skilz to do some of the sweet work some of the guys here do.

Buggy seems to be running okay. A few initial thoughts
- the shocks seem very soft, I wonder where I can get some replacements that are a little firmer and the right size.
- I started with a 13T pinion and the motor was running pretty warm but the ESC was cool - I'll try to gear up a little to even that out.
-max Amp draw was recording right about 50A using a 3S lipo pack (still haven't gotten the replacement A123 charger yet)
- I need an antenna mount because it's just hanging loose right now

Pluses - I am very impressed with this buggy for $250. I could easily see this little guy put my LST2 on the shelf for a while.

With Mike's motor mount the whole project was made very easy.

I want to use a plastic spur gear - but I think I'll wait to see if Mike ever has one just for this buggy - I don't want to drill too many holes in the chasis.

Oh yeah - one more complaint (or whine) is that with the motor mount and servo setup it is impossible to change a pinion w/o first either removing the servo or removing the whole center diff assembly.

You just can't get to the bottom screw with the servo in the way.

Yeah, that does suck. I thought about making some sort of quick-release for the servo since that would probably be easier to remove quickly than the CD.

Just fyi - I meant to say BATTERY mount. Mike's motor mount rocks!

"Here's a few pics of what I've done so far. The motor mount isn't great (just some L-arms from Home Depot cut to fit along with velcro tape and velcro straps - but seems to be holding well for some trial runs) - I just don't have the tools or the skilz to do some of the sweet work some of the guys here do."

It looks great!! Nice job on it! What Hacker motor are you running in there?

Hey, thanks. It is a Hacker B50 8L (3019kv) motor. Very solid, in my opinion not quite worth the money ($180) but I already had the MM esc. I would place it somewhere halfway between a Feiago and a LMT/Neu. Strong power, but you can feel the pull much more when you use a LMT.

Still a lot of tweaking to do........ but that's just part of the fun.

Looks good! The crt.5 is a great truggy to convert, you will love it.

Its funny how much different my crt.5 looks than others. With the ext. chassis, 1/10 2.2 rims+ tires, full size servo and larger wing+ body its a completely different truggy. I really need to post up a thread of my own, just waiting for the new lipo to arrive (TrueRc 4s 4.2Ah custom pack).

Bye

Hacker 8L.....good ol'days..=)

Definitely post a new thread on it. =) Let us know how the TrueRC lipo pack does. Does it have the same C ratings as the 6400 or 8000 TrueRC packs? Or was it built completely custom to fit your battery tray on the CRT.5? How much did it cost to make if you don't mind me asking?

I'll post up a thread when I have time, just starting school again and have some summer work to catch up on! The pack is a 15c cont. 20c burst. It should hold up fine, if it doesn't Dan @TrueRc has some 20c cont. cells if I need to upgrade. It is just a custom pack by that they usually sell them in a 1p format, I am getting 2p (4200Ah). The cells are only 102mm long and 35mm wide(as opposed to 135+mm long and 45mm wide) so they should fit much better than a standard lipo size pack, though it will be 50-60mm high because it is a 4s pack. Also you have PM about the price of the pack...

Bye

Since I've never had a Hacker before, is that a good thing or a bad thing?

I really wish I could get a LMT 1930 for the buggy.

I have a 1950/7 that I imagine I could gear really high - but I think it just weighs way to much and the benefits would be so minimal.

Just thought I would share some updated pictures of my CRT.5. The conversion is almost done after some tweaking.

Decided to run with my MaxAmps 3S 5000mAh in addition to the 4s A123 cells. The 5000mAh pack is just a great fit for the buggy.

Had a problem with the kingpin screws - they are not Locktited! Had one fully back out and got lost in the field - really glad that Ofna included an extra screw pack (that's a really nice touch)! When I went to replace that one I saw that two of the other three were almost completely backed out as well. I was actually surprised to see that the steering arms have metal inserts for the kingpin screws to go into (another nice touch) as I just assumed the screws were going into the composite plastic. They are all locktited now for sure.

Also - went with the 17T pinion and temps are all in check right now.

Filled the diffs with 7/7/5 as the front end was really pulling up and ballooning the front tires something fierce with 3k in the center.

Was getting some pretty bad glitching, so went with Cemtery Gates' ferrite ring solution in this thread http://www.rc-monster.com/tempforum/...ighlight=crt.5. Seems to be helping a lot.

Just got a React at a pretty good price off of Ebay, so that will be installed sometime next week. (Radio, 2 transceivers, 2 temp probes, 1 voltage probe, 1 speed probe all for $300:mdr:)

Nice! How are the temps for the ESC/lipos/motor?

I lost a kingpin screw and one of the inserts on the track. Like you, I've since lock-tited everything. Yeah, it comes with a screw pack, but no extra inserts. Grrr.

Got the buggy out for the first real runs today. Temps seem to be running a little on the high side with the shell on. I got it out for the first real test today - motor temps were stable at 140* and the ESC at 170*. The MaxAmps 5000mAh 3S lipos only got to 100*.

I think a little ventilation will help the ESC temps and I am going to put some heatsink compound on the motor heatsinks which should help a little bit there. I upped the Punch control on the MM from 20% to 50% as the front end is picking up a lot during acceleration.

Thinking of trying a 16T pinion to help out the temps too.

Pinions wear on the 17T has been really good.

This is a fun car!!!:intello:

Main problem I am still having even with 7K diff oil in the center diff is that front end is picking up and unloading a lot causing the front tires to ballon rediculously when I go for hard acceleration - if anyone has any recommendations to help in that regards please let me know.

Just painted a Pro-Line Crowd Pleaser body for the car tonight (will post pics next week when it dries and I get it cut to fit). I was a little disappointed in how thin the Lexan on the Ofna body is 0 the Pro-Line body is a much thicker Lexan.

OK - couldn't resist - here's a shot of the body I just painted this afternoon.

The car and body look awesome!! Nice job on both. Post some pictures of the body mounted, will you?

Heh, I do bodies the same way (one color fades to another). My bodies are blue in front and fade to black. That combination of colors looks good, and will certainly match the stock-type wheels.