CR-01 Bronco Build

[Pathung]

I recently purchased a new CR-01 Bronco kit, and have pretty much finished building it now, except the painting of the body. I've run it a few times on the driveway, over firewood logs and a pile of rocks in my yard, and it does quite well, though I wish the tires had more bite.

During the building process, I posted in another thread regarding suggestions for suitable ESCs for the truck, and thanks to all who responded, I went with the Novak Rooster Crawler/55T motor combo, for about $100; the combo lacks top speed, but the crawling is just right. I use a Futaba 3PL transmitter with a standard Futaba servo, so far I haven't paid much attention to the servo yet because I have another problem that needs your feedback, if you will:

After installing the rear axle and hooking up all the electronics, I switched it all on, and noticed that the left-rear wheel would "slip" while turning (while I hold the truck up in the air), as if the axle pin wasn't lodged correctly. I switched wheels left/right, and the same thing happens. I then noticed that the right-rear was doing the same thing, but not quite as pronounced, so I didn't notice it at first. When viewed from behind driving on a flat concrete driveway, the left-rear wobbles while while the right-rear doesn't. so I'm thinking that something's wrong in the drive shaft to wheel pin area in the L/R, and have taken it out a number of times, to no avail. As far as I know, I built the rear axle as I did the front axle (which isn't having problems), and don't believe having left out a bearing or parts. Before I tear the axle apart, does anyone have suggestions/experience on this? The truck's brand new, and the gears looked fine when I installed them... I'm hoping that I don't have to go all the way to the planetary gears to fix this problem.

Photos of the chassis without electronics, and Novak ESC/55T motor awaiting install; it's all been installed and the truck running now, albeit still without a painted body:

[cartronicshn]

Check the hexes and the wheel hexes for any deformity.

[click the pirate]

I did not like the stock plastic hexes, so I bought some aluminum hex drives made by Losi, the are a bit narrower, but that did not affect mine with the stock wheels. I like this set up much better, good luck!

[Pathung]

Thanks for the suggestions of checking the hexes; I did, and didn't see any damage there.

Looking at the truck more closely, to my great surprise I noted that drive shaft's longitudinal ridges were twisted in one direction! I'm not sure how this would've happened, but thought it best to rebuild the rear end. I took everything apart, and noticed that only about 50% of the pinion gear was in contact with the diff. gear. I played with shimming (with the included 0.3 mm Tamiya shims) the L/R axle to bring the diff. gear closer, but later decided the correct thing to do here is to instead shim the pinion gear to bring it into the differential gear some - I used two shims, bolted everything back together, and now the wheels turn smoothly. I guess my problem was the pinion gear not meshing deeply enough with the diff. gear, causing some slippage. Turning both axles by hand, the rear axle is harder to turn, possibly due to the larger contact patch between the two gears - I'm hoping that with time running the truck the gears will wear a bit and eventually mesh appropriately.

Since one of my driveshafts was destroyed, I bought a set of Integy shafts, coming from Tower. If nothing else, the blue breaks up the monotony of an all-black driveline

[DRW-FJ40]

Hey Pathung, Sounds like you got your slippage figured out. Odd, I've never heard of that problem before, I would have leaned toward the diff lock set screws but... If you got it, good.

You have discovered two common issues with the CR01, axel grind when new. you can find a lot of threads on this one & bottom line is run a few packs threw it & they will "break in" & spin freely.

The other is the week link in the drive train, the plastic splined shafts. The problem gets worse as you add more torque to the motor or wheel weights. A cheap fix is to put epoxy in the hollow section of the shaft to strenghen it. I personally haven't tried this. What most do is upgrade to steel shafts as you are planning. I only have experience with Junfacs and Tamiya steel hop ups. Of those two, the Tamiya have worked great & the Junfacs failed misserably and customer support at Junfac seems to be non-existant. I couldn't even get them to respond to an email. Any steel shaft though simply transfers the week link from the splined section where the two shafts connect to the pins & set screws so... get a little piece of shrink tubing or electrical tape & wrap around the shaft in a way that if the set screw comes loose, you don't loose all your stuff. And obviously, loc-tight the set screws.

Be sure and post pics and let us know how the Integy's work. I just got some Integy shocks for mine & they are beautiful. Haven't tried them yet though. Stock shocks leak oil but to tell the truth, I haven't noticed from a performance standpoint, I just got the Integy shocks to add a little blue bling to the chassis.

[860Crawler]

Junfac can be pretty slow with responses. I've emailed them a few times about older CR-01 parts and they always got back to me eventually. A lot of their CR-01 parts are out of production

[Pathung]

I'm surprised that the little amount of slippage in the rear diff. could cause that half-shaft to twist and stay twisted like that (see photo - reminds me of rigatoni). As you stated, metal shafts merely transfer the 55T's torque to the pins; I'll watch for that. Hopefully with the correction of the slippage problem, that previous source of intermittent but high resistance in the rear end has completely disappeared; I'll run the remaining good plastic shaft to the rear end for a few days to see if any twisting occurs... the front will be using one of the Integys received, or I can leave it in 2WD for a while, but what fun would that be?

UPDATE (8 hours later): So I did leave it in 2WD today and ran it around inside the house; soon the good drive shaft fell off! The splined shaft TWISTED OFF from the coupling. Wow. The gear mesh area is larger, and mesh tighter than before due to my adjustments (consequently no slippage), but is there now too much CONSTANT resistance? The front axle turns a great deal smoother, with barely any grinding noise. I'm thinking of buying a new pinion gear next... what's my problem here?

Another matter: Novak's instructions stated that the ESC should be as far away from the radio receiver to avoid interference, so I now have the two components at different ends of the truck; has anyone found this little warning to be of concern in everyday operation? I've seen photos on the forum of all electronics packed tightly together in a waterproof container...

Photos of the finished shell on chassis (in Tamiya's Mustard Yellow), and finally, the twisted drive shaft.




https://lh5.googleusercontent.com/_J...0/DSC_1257.JPG

[Pathung]

I'm starting to think that there's something wrong with my bevel gear; is there another brand out there complete with shaft that I can buy?

[DRW-FJ40]

the twisted splines in the prop shaft aren't from your sliping diffs. It's just a weak spot in the stock truck. slipage or not, tourqey motor, wheel weights, running it on carpet, anything that puts extra tourqe on the drive train will twist shafts.

Your slippage/axle grind is a bit of a mystery. Like I said, some axle grind when new is normal but it's hard to say from a description if you are in a normal range of grinding and should just run it a little more or if something else is going on. Here is what I am thinking...

The slipage is weird. I didn't have to shim anything to get my axels to work right. you can search multiple forums and find numerous threads where people have put their CR01 axles together, felt resistance that seemed "not normal", taken them apart, studied the directions only to conculde that they haven't made a mistake, post to some forum and have people respond back that it's normal & problem goes away after a few packs.

What is unusual about yours is the slippage & only the rear is doing it. Have you double checked the diff lock screws?

Did you have the same amount of resistance before you ran it in 2WD? could be you are starting to see some break in on the front.

The grinding issue, if I'm not mistaken, is due to a imperfection in the bevel gear. (someone correct me if you know otherwise, but I think that's the case). it my be more irregular than others which would explain the slippage and more grinding. but with out be able to dive into it, I'm grasping at straws here.

I placed my electronics in the places indicated in the directions which you can't really get them to far apart, and I haven't had any interfearance issues.

BTW, truck looks great, I like the color. Looks like a nice clean paint job.

[DRW-FJ40]

Might try posting on Tamiya crawlers too:

http://www.tamiyacrawlers.com/forum/index.php

[Pathung]

Well, I decided to take the rear end apart again to see if undoing the diff. lock pin makes a difference. It didn't, but I noted that as I shimmed the bevel gear to push in more, the ring gear was now pushed back against the back of the plastic casing, and leaving a trail of grease on the casing itself; I over-shimmed the bevel gear, obviously. I checked the ring gear's teeth, and they seemed okay. Next I examined the bevel gear (mostly to take away one of the two shims to see if that's a good compromise, and I noticed that the bevel gear had cracked! In the photos attached, chunks can be seen missing off the rear "wall" of the gear, with one of the pieces next to the gear.

Looks like I'll have to contact Tamiya for a new set, as this should definitely be under warranty - the truck had about 30 minutes on it, and I'm still on the first battery charge!

Any other suggestions? I'd much rather find another source/manufacturer for this bevel gear, if I can. I looked at Robinson Racing's website, but it seems they mostly do motor pinion gears.

[Hyperman]

Originally Posted by Pathung

Well, I decided to take the rear end apart again to see if undoing the diff. lock pin makes a difference. It didn't, but I noted that as I shimmed the bevel gear to push in more, the ring gear was now pushed back against the back of the plastic casing, and leaving a trail of grease on the casing itself; I over-shimmed the bevel gear, obviously. I checked the ring gear's teeth, and they seemed okay. Next I examined the bevel gear (mostly to take away one of the two shims to see if that's a good compromise, and I noticed that the bevel gear had cracked! In the photos attached, chunks can be seen missing off the rear "wall" of the gear, with one of the pieces next to the gear.

Looks like I'll have to contact Tamiya for a new set, as this should definitely be under warranty - the truck had about 30 minutes on it, and I'm still on the first battery charge!

Any other suggestions? I'd much rather find another source/manufacturer for this bevel gear, if I can. I looked at Robinson Racing's website, but it seems they mostly do motor pinion gears.

From this thread on RCMT.biz you can use RC4WD Highlift HD spools.

I cant vouch for how reliable the info is as I haven't tried it.

http://www.rcmt.biz/bd/showthread.ph...letproof-Diffs

Hyperman

[Pathung]

Originally Posted by Hyperman

From this thread on RCMT.biz you can use RC4WD Highlift HD spools.

I cant vouch for how reliable the info is as I haven't tried it.

http://www.rcmt.biz/bd/showthread.ph...letproof-Diffs

Hyperman

Thanks, I'll give RC4WD a call to see if the steel bevel gear will work in CR-01s... the ring gear doesn't look half bad either. I can't believe that they used pot-metal to cast these gears.

[DRW-FJ40]

Yea, looks like you had a defective bevel gear. Normally the pot metal is a non issue because there just isn't a lot of stress at this point but... sounds like your on track. If it were me, I would try another stock tamiya. I could see how you would be a little gun shy but I think you just got a lemon.

[cydog510]

the bevel gear problem is happening quite a bit.
to me for example, 3 times....
t

[Pathung]

Originally Posted by cydog510

the bevel gear problem is happening quite a bit.
to me for example, 3 times....
t

Were you able to get Tamiya to send you free replacements? What are you using now? I read your posts elsewhere, so knew that I wasn't alone in this...

[cydog510]

i just bought 4 of the bag at the same time, but if one more goes i am going to get the steel one mentioned above, it's pretty frustrating breaking down that axle, especially when its in the front! i also have the Reinforced Drive Shaft & Diff Lock ready to put in when i open the diff next. i didn't send it in to tamiya, i would suggest buying a replacement and giving it a try to get a new one from tamiya USA. good lucjk and let us know how it turns out.
p.s not sure if the beadlocks are installed correctly on your wheels, if you have a close up picture, it would help.

[Pathung]

I don't want to have to take this axle apart again, so I sprang for one of the RC4WD steel ones this morning. I'll post about how it fits and works when I receive it later in the week. I e-mailed RC4WD to confirm that it works for the CR-01, but never got a reply back; they do have a money-back policy, so I'll just return it if it doesn't fit.

I didn't put in all the screws on the beadlocks, figuring nothing's going to fall off; I'll post a closeup photo tonight.

[DRW-FJ40]

Didn't know anyone was having trouble wiht the bevel gear. I've beat the daylights out of mine & never a problem. now driveshafts, that's a different story.

P.S. just saw Cydogs post. I think you confirmed somewhere along the line that the gears were deffinately slipping but it's worth mentioning that other people have experienced "slippage" only to disscover that tires are slipping on wheels.

Let us know about the RC4WD gear. they make some really cool stuff but not always the greatest about answering emails or directions. That said you can usually find answers on the forums

[Pathung]

I don't think that the tires were slipping on wheels, as I was holding the truck upside down, and the wheels/tires had no load on them.