CRT Conversion Questions
 

I am planning on converting a CRT to BL and have been doing some homework by reading past builds etc.

Here are my remaining questions:

I have the stock spur right now and its huge. Are there smaller spurs that will fit on the stock center diff so I dont have to buy a whole new one?

And if I ran the Castle 2200kv motor, would it make more sense to go with a 5s vs. the 4s? Im not racing so that isnt an issue. I'd probably like to gear for around 40-45 mph tops.

Thanks in advance guys :smile:

The stock spur is huge cause the crt uses buggy ratio, 43/13, diffs. Most truggies use a 10/43 diff ratio, and can get away with a smaller spur and still have a similar overall rollout with the taller tires that truggies run compared to buggies.

You can swap the ring and pinion on the crt for hot bodies lsp parts to get the 10/43 ratio. Then you can run a 46t or similar spur. I did this with my old crt as I wanted to use the kyosho plastic spurs.

the CC motor would be better with 5s and lower gearing than with 4s and taller gearing. It will also open up battery choices a bit, as 4s in a truggy will require really good lipos, like polyquest 6000 packs. You can drop dowm to 4500-5000 mah packs with 5s and that opens up your choices quite a bit. 4s in heavy vehicles is not really a good idea, in my opinion...

Hey thanks for the reply man. I shot you a PM with a few more questions.

My CRT build is done and I used the stock 62t spur with a 13t pinion, 2200kv cc motor with 5s, radar at 43 MPH with loose traction, proved to be enough for me if it wasn't I would use a 15t pinion.

Thanks fsracer, good to know I could still use the stocker.

What kind of temps are you getting?

Mike also sells the Kyosho plastic spurs for a few dollars...and they hold up well. I have a couple of extra center diffs with a 44T and 46T spurs for my CRT. This offers a lot of options for gearing.

Well the Kyosho spurs bolt right up to the stock diff? Im on a pretty strict budget right now, so I wanna keep my costs down as much as I can.

Yes, the Kyosho spurs are a direct fit to the CR and CRT X1 and X2 diffs.

Sweet! Just what I wanted to hear. Looks like I will have to take a look at them.

Here is the link to my buildhttp://www.rc-monster.com/forum/showthread.php?t=17637, after 20 minutes of hard driving I still can't get the Monster fan to turn on which is factory set to 150f although the ambiant temp up here is cool 50f.

I went with the ofna hyper st truggy diff in my build with 14t pinion I'm around 40ish and temps are perfect, plus it's an 8 spyder center diff versus a 6 spyder and it's 52t versus the stock 62, makes a huge difference in room... :yes:

Awesome, thank you for your replys guys.

I think I might take a look at those Kyosho spurs. That will be the cheapest alternative, and give me some more room for the battery placement.

you won't be disappointed with the kyosho spurs on stock CRT diffs. Spider 8s look cool and they are robust but they are also high maintenance because they are prone to leaking. After owning several spider 8 sets, I have grown to prefer the Jammin and/or HB diffs...especially the spiral cut ring and pinion versions.

Sweet, that definatley seems like the smartest thing to do. Now I need to sell some stuff to fund my MMM Combo!

I can attest I am very very very happy with the MMM combo in my BL CRT just watch my vid in my build thread :whistle:

I just looked up the Kyosho spurs the Mike has in the store, they look good and heck they are cheap!

It says you cannot used hardened pinions with them though. Arent all the 5mm mod 1 pinions hardened?

I don't recall it saying that in the past. I have had several conversions with the kyosho spurs and haven't had any problems. Obviously the steel spurs are optimal but plastic should be fine if your gear mesh is correct and you use appropriate diff fluid.

Cool, looks like I'll just have to make sure I check my gear mesh twice on this rig.

Another question now on battery and motor combinations. I think Im gonna go with the Castle 2200kv motor and am trying to decide between the 4s and 5s Zippys. I will be using the Kyosho 46t spur, and not sure on the pinion yet.

Any recomendations?

5s and gear it down slightly. 4s requires good batteries to perform optimally.

Keep in mind that you will ne going from a 62t spur to a 46t spur... You will need some small pinions.

Here is the setup with the 46t kyosho spur, and a cc 2200 motor on 4s lipo...

Differential Ratio: 3.3076923076923075
Transmission Ratio: 1
Other Ratio: 1
Spur Tooth Count: 46
Pinion Tooth Count: 11
Total Voltage: 14.8
Motor KV: 2200
Tire Diameter (inches): 5.75
Tire Ballooning (inches): 0
Motor Current Draw: 0
Motor coil Ω: 0
Spur/Pinion Ratio: 4.18 : 1
Total Ratio: 13.83217 : 1
Tire Circumference (inches): 18.06 inches (458.83 mm)
Total Motor Speed: 32560 RPM
Vehicle Speed: 40.27 mph (64.68 km/h)
Effective KV Value: 2200

If you do not change the diffs you will most likely have to stick with 4s, as 5s will require tiny pinions to work. As far as 4s lipos go in the zippy line, the flightmax 5000 30c 4s pack is most likely the best bet. You really need the lsp diffs to give you some more gearing options with the kyosho spur.

Now if you stick with the stock spur, and go to 5s:

Differential Ratio: 3.3076923076923075
Transmission Ratio: 1
Other Ratio: 1
Spur Tooth Count: 62
Pinion Tooth Count: 12
Total Voltage: 18.5
Motor KV: 2200
Tire Diameter (inches): 5.75
Tire Ballooning (inches): 0
Motor Current Draw: 0
Motor coil Ω: 0
Spur/Pinion Ratio: 5.17 : 1
Total Ratio: 17.08974 : 1
Tire Circumference (inches): 18.06 inches (458.83 mm)
Total Motor Speed: 40700 RPM
Vehicle Speed: 40.74 mph (65.44 km/h)
Effective KV Value: 2200

This would be a better setup. I would still suggest the flightmax 5000 30c 5s pack for this. It will weigh more, but you wil get longer runtimes, and the equipment should stay cooler with the lower gearing. Plus you can go up a bit on the gearing, 13 or 14t spur and pick up speed without over drawing the batt.

FWIW, I'm quite happy with 13:62 gearing on 4S with a 2200kv Neu. It runs in the mid-high 30's and everything stays quite cool. I'll probably be changing to a 14T pinion soon for higher bashing speeds, but it's quite fun as is right now.

Wow, thanks for all that awesome info lincpimp. I have been playing with that gearing calculator too, its a great tool!

Do you have a link to the Flightmax 30C 5s? All I can find is this one and its a 20C : http://www.hobbycity.com/hobbycity/s...idproduct=8581

ZIPPY Flightmax 5000mAh 5S1P 30: http://www.hobbycity.com/hobbycity/s...idProduct=8589

What about ZIPPY Flightmax 5000mAh 5S1P 25C http://www.hobbycity.com/hobbycity/s...idProduct=8585

FYI, weights are 632g, 628g and 650g for the 20C, 25C and 30C, respectively.

Also, it is roughly $15 more to get 25C from 20C, and another $15 to 30C. Obviously, the higher the C, the better, but is it really worth the price and weight difference? It might be that the 5000mAh 5S1P 25C is optimal.

What do you guys think?

I'd like to know myself since I'm planning my next conversion - just got a Hyper ST Pro kit yesterday.

Oh, hobbycity also has this helpful battery filtered listing tool, which I used to find the above packs: http://www.hobbycity.com/hobbycity/s...figuration.asp

Awesome, thanks for the links flipmac. Not sure how I missed those?!

Looks like I will be going with the 5s... just need to decide if the 30C is worth the extra 15 bucks or not.

If you plan to gear for around 40, and are not trying to build the worlds heaviest crt, the 25c 5s pack will be fine. If you were going with 4s, the 30c would be a must. I really like 5s, as it takes a load much better than 4s and the addl weight is not really noticeable. 15 bucks is about the same as the faster shipping costs, which I do recommend. If it will not break your bank acct, and the 30c batt will fit, why not buy it. It will provide better performance, and will handle higher gearing if you want. These packs have not been tested throughly, but for the price you can hardly go wrong...

Sounds like I'll do the 5s. Thanks for all of your help lincpimp, I appreciate it.

Just checked the Hobby City site and both the 25 and 30c packs are out of stock... crap.

Buy a few of those Kyosho spurs, they will break on you sooner or later. You'll get good at tearing down your truck to replace the spurs. I like the hardened steel option much more combinened with the hot bodies lsp diff and pinions. The Hot Bodies parts are nice. I really like the spiral cut gears. If you have the money this is the way!

Yeah, I am in the same boat with the 6s 30c packs... I may just backorder one, but I am not sure yet.

No prob with the help, that is all I am here for... and a little comic relief.

Thanks cartwheels. Once my money situation becomes a little better, I might go that route, but for now I think Im gonna end up using stock gearing.

Any idea how long it takes for them to come in? Im not too familiar with Hobby City or their Lipos.

Hey,


Just to chime in about my X1 CRT build. I am running the MMM 2200kv combo, stock 62t spur with a 14t pinion, and 4S 5000 mah Zippy Flightmax 25c batteries. I ran this combo at the track last Saturday for hours without a problem.

The Zippy's seem to perform very well in my limited testing. I didn't bother to take any temps because everything felt to be under 100 degress to my touch.

I have also tried a 13t pinion, but I had problems with the mesh. It would clack as it was braking. It seems that pinions with higher tooth counts mesh better. I would really like to try a 16 tooth pinion with this combo. I've found that with higher tooth counts I tend to get better acceleration because the torque does not hit the wheels so hard causing spin (thus less acceleration).

I will say that if unlimited traction were available, lower gearing would produce faster acceleration, but in the real world where I can spin my tires at will even on pavement, higher gearing gives me better acceleration.

...(On Hobby City order time: I live on the east coast, and with EMS shipping I have seen order take anywhere from 3-5 days on average)

Thanks for the info man I appreciate it. Seems like 14-16t pinion is the way to go and is what most people are having good luck with. Im waiting for the Zippy Flightmax's to come back in stock on HobbyCity now....

Any ep diff between x1 CRT vs x2 CRT?
 

Hi, I m currently racing with my x1 CRT. was thinking to change to x2 CRT. I m using Rc monster's motor mount n servo tray. izzit worth d change n can I still use d same conversion kit?? I m using big bore shocks btw.pls advise thx