Cross RC BC8 8x8 Build

[HumboldtEF]

Its here!!! I'm exited to start putting it together tonight

I need a bigger table stat!

I've been wondering what a 560 sized motor looks like, next to a holmes sealed can 550 motor the Cross Rc motor is 8mm longer. I'm thinking a nice 550 motor might even out perform this simple sealed can motor. I like the idea that it can most likely be upgraded as I was afraid the 560 size would rule that out. Oh and the tranny comes assembled, I'll do a tear down to ensure all is good though.

Its a nice touch to include some tools besides the usual L (allen) wrenches

For a sense of scale next to a proline SR5 SCX10ii and a Gmade Gom

Oh and look at this ultra compact sound system, My god the size of this is just hilarious.

The tires felt pretty good a bit on the hard side but sticky (they remind me of the rubber from bike tires actually). I'll soak them in simple green to soften them up a bit more. the steel wheels are damn heavy though there are 8 of them so there's that.

I noticed there are some extra parts included at a quick glance, there are two different types of doors to choose from. they also included the plastic suspension components as well as the metal ones. But im not sure what purpose those plastic parts will play since the standard version thats meant to use them has seemingly been pulled off of their site, spare parts I guess.

First they start you off building the "shocks" which have an internal spring.

I believe they were 73mm eye to eye

They feel decent for an internally sprung shock the o-rings do an ok job of dampening the spring. Theres no chance of assembling this with oil it just wouldn't work.


Then on to the Trailer hitch and I can see this is going to be one of those builds where they have you jumping around a bunch

This thing is damn heavy weighing in at 12.7oz, I'll likely be making a styrene bed or something for the rear so I'm probably not going to use the hitch.

Mounting the tires is next but I'm skipping that since I'm currently soaking them in simple green to soften them up and clean up the mold release agent

Heres the tranny opened up, it was greased well

Its pretty massive and the layout is a bit different, theres no large spur gear. the 2 speed sort of dog box interface looks good

It has an inspection cover for checking gear mesh though you cant access the bolts that mount the motor to adjust from here which is unfortunate, it will take some trial and error/assembly and disassembly.

To check that all is well with the tranny they recommend connecting your (7.4v-11.1v) battery directly up to the motor so you can listen for anything wrong. Seriously WTF :roll: thats a terrible idea, you can simply stick a hex driver or something skinny though the output shaft and spin it by hand, or use two AA batteries.

On to the diffs and transfer cases.
The spool and diff gear are all one piece which is nice. I was expecting sintered metal but it looks like it might be something else I'm not entirely certain what, maybe cast with some machining.

some of the parts, it uses lots of C and E clips, bit of a bummer

assembled, they spin freely after I got all off the bearings seated. They mention not to use a bearing on one side of the input gear on the transfer case, not sure why, I used one but might need to round up a few more bearings later on im guessing.

the left side suspension arm assemblies

So far Im pretty pleased, though I'd be happier if there were less C & E clips used. Theres one page mostly in Chinese that lists batteries and voltage, it shows 11.1 volt Nmhi & Nicd or 7.4v Lipo. I'd like to be on 3S ideally but I might be pushing my luck possibly. 12.4v isn't too far off of 11.1v but its probably the snappyness of the lipo that's the issue.
Lots of heavy metal parts in this kit. Their tools are working nicely they have a good tight fit. Hardware has seemed good so far, all hex. Instructions are not the best but they work,

Notice how they call for using wire cutters to hold the shock shaft, odd and I tried to use my shock shaft pliers but it was proving too hard to compress the spring while grabbing the shaft with the pliers so I resorted to their method which was fine but sounds a bit crazy.

they've amended the standard version manual to include the parts for the flagship version with stickers showing different part numbers and half pages glued in to show the correct steps

 

[jebster]

I'm excited to see someone building this rig. It is high on my wish list.

 

[bent_hinge_pin]

Love the spintires pic on the box. Cant wait to see this puppy in action its super cool

Sent from my LGLS991 using Tapatalk

 

[HumboldtEF]

RPP is where I would get this from Though they weren't a dealer when I picked mine up.

https://www.rpphobby.com/product_p/czr-bc8f.htm

 

[HumboldtEF]

the rear suspension assembly

This quite a few steps ahead but heres the rear suspension, a pivot type not sure what to call it.

29" long chassis rails, extruded aluminum 3mm thick, painted black with some metal flake in it. I already attached some small rectangular brackets, one which had holes that were slightly off, I opened up the three holes to 3.2mm to get the bracket to mount (was only for 1 out of the 8 brackets)

The diff/transfer case assemblies go in first

2 steering servos are required. I found out on a later step that these Savox 2290's sit a little low and were pushing on the sort of bellcrank linkage so I cut a few pieces of .060 styrene to raise both servos up. Its now higher than it needs to be but fine.

One important thing to note is that you'll need to get steering servos with 25t splines in order to use the Servo Horn, and its not your typical servo horn. (I got lucky)

Also worth noting you will need to come up with a 14mm servo horn for the shift servo (they really should have provided this one). I was able to use the basic plastic horn that comes with the Hitec servo I used, I just drilled a hole big enough to use it (at 14mm)

The drive shafts look really nice, they look JunFac sized but with a nice beefy splined center

Tranny and motor mounted

Rubber bump stops for the front & rear suspension

2 speed shift servo and linkage

Torsion suspension for the front, these slot into the A arms. They provide 2 different plastic jigs that clip in place under the A arms used for setting the firmness and ride height of these.

I went with the standard setting. Once its were you want it you'll tighten the screws that clamp down on the other end of the torsion bars.

I mounted all of the tires last night and they went together very easily which I was very thankful for after my last set of wheels (BoomRacing) gave me hell. They are steel wheels, theres some ribbing on the inside of the tires for sidewall support and the rubber is very grippy after a soak in simple green (they started out sticky too). I've layed them down on my laminate floor and they're so grippy I can hardly push them around (not a useful scenario just interesting)

One thing I had to do when assembling was make tiny adjustments to get the two halves aligned just right as theres a bit of slop in the holes. So once I had the screws started but not tight I would check and adjust this alignment and then tighten it down. I originally thought I had not picked the right holes for the proper alignment but after reassembling a few I realized I had the right orientation just that there was just some slop that could allow the holes on each half to miss align ever so slightly. These come with a hubcap so it should be hidden but I just wanted them to be presentable in case I decided not to use the hubcaps.

the back of the wheel uses a separate hub which is nice

EDIT: I just weighed all of the tires, 5lb 8oz :shock:

 

[HumboldtEF]

Well I got it up and running this weekend, I got the dual steering dialed in easily which was nice cause I assumed it might be a pain. I used pretty much the full travel of both servos. The linkage in front is a few mm longer than the rear (2nd axle) which does the job of steering more up front than in back so it doesnt need to be setup through the TX.

They even have a provision for people running both servos on the same channel, they've got a slotted adjustment built into the steering linkage so you can manually center the axles independently.

I found one sheet metal plates that go on the bottom of the chassis had the hole pattern 180 degrees off.

It lines up when rotated 180* but the holes are meant to access parts inside so putting it on backwards is not ideal.

the holes are 1/8" off

I slotted and countersunk the hole to get it inline, and touched up the paint afterwards.

a few more bad news items, the cooling fan has been struck by something and one of the support arms has broken off and the blades hit the housing when I spin it by hand. Not a huge deal as i might not even use it but I'll let them know about it and the lower plate.

I'm also working on eliminating the slop in the rear axles, they have maybe 5mm of play. Using some 3mm-ish sized washers I tightened up the A arm pivot on the outer portion (the inner is much tighter). You can see as you drive as the wheels slip loose they can wobble around back and forth, pretty annoying but I just test my fix and I'm down to 1mm of play or so.

I started to slowly assemble the body using Bondene (acetone)

EDIT: I wanted to correct something I mentioned earlier about not running on 3S (I haven't really gone over the manual top to bottom to seek this out), they do mention using 2S as well as 3S in the wiring diagram so my fear of it not being built to handle 3S seems unfounded which is awesome. I did a test run on 3S and I can imagine 2S would be pretty slow.

A few more tidbits to share after driving it, its about 16 lbs without the body which I'm guessing will add 2-3 lbs the steering it pretty nice for such a long rig and the linkage seem to work well. The tires remind me even more of bike tires due to the sounds they make, they grip pretty well and dont show any signs or wear yet which is surprising because its so heavy.
The front end is as long as a Lincoln which I expected, but you send a lot of time finding the line which will allow the long front though, kind of like a lowrider taking driveway at an angle, lol. Once its up on the obstacle all is well, it monsters up just about any angle I tried. It will get high centered easily so you need to look out for that too.

1st gear is a very slow crawling gear (lots of torque) which it really needs to pull all of the weight and avoid bogging the motor while going at a snails pace. You can crawl in 2nd but if you try a very slow speed its easy to lose power/bog the motor going over a small rock so you need to be a bit more aggressive with feeding in throttle to avoid this.
2nd gear is a bit faster but probably about as fast as this should go.

this is using the smallest pinion they provide (9T I believe)

 

[Gregorius]

How tall is your servo? I installed Savox 1230SG but they are too tall so the main body floor won't seat properly. Thinking about doing a cutout for the servo to poke into the body.

Also I never had a problem aligning the metal under body plate. I'll take a look when I get back home.

 

[HumboldtEF]

How tall is your servo? I installed Savox 1230SG but they are too tall so the main body floor won't seat properly. Thinking about doing a cutout for the servo to poke into the body.

Also I never had a problem aligning the metal under body plate. I'll take a look when I get back home.

I spaced my servo up and dont think its interfering with the body sitting flush but I will take a closer look and report back. I just looked up the specs and your servo is 44.9mm tall and mine is 38.7mm and I raised it 1.5mm so really 40.2mm

The metal plate aligns just fine if you rotate it 180* and then install it (though I may have gotten one from a bad run possibly) you can use it this way but the access holes in the plate wont line up with the parts inside. I guess the other possibility is that the hole pattern on the chassis was to blame and not the plate and that they fixed the issue mid run.

Its nice to hear that someone else is building this thing "thumbsup"

Did you also have excessive play (front to back) in the rear axles/suspension assemblies? Just curious, and I think I've found a good simple solution that I mentioned in the post above. I'll post up more details that I left out later tonight.

EDIT: I just checked the clearance I have on my steering servos to the main body bottom and its 5mm from the servo top to the bottom of the body. Measured from the top of the chassis rail they stick up 12mm above it. From the servo mount bracket (from the top) it measure 29.5mm to the top of the servo. One thing I've noticed about putting the body on is the motor wires are very tight and you need to bend them a bit and squeeze your way past them, could that be part of it?

 

[HumboldtEF]

I took a quick video of the play in the rear axles, all 4 rear wheels do this, theres about 5mm of play. the front is assembled the same but the steering linkage kind of negates this a bit but It's probably worth tightening up both the front and rear.

<iframe width="560" height="315" src="https://www.youtube.com/embed/y3CyeKRqy48" frameborder="0" allow="autoplay; encrypted-media" allowfullscreen></iframe>

https://youtu.be/y3CyeKRqy48

I found a normal hardware store washer tightens it up enough to reduce the play down to 1mm or so after doing this to 1 of the 2 pivot points. the joint is still nice and free, not sticky or tight.

it measures 8mm diameter, 4mm inner diameter and just a sliver under 1/32", my guess is that its a washer meant for M4 hardware but the main points are that it has at least a 3mm hole and is about 1/32 thick, you'll need 8 to do the back (and the front could benefit too)

I put this washer behind the brass bushing that runs through the A arm.

this bushing runs through the A arm and stubs out a few mm on the other side

there's also a thin shim used on this end that hangs off of/is held in place by the stub that sticks out. This stub sticks out farther than the thickness of this shim. I found that the thickness of my washer was a perfect fit to take up this slop if i sanded of the extra bit of the bushing that stubs out past the shim. I took the bushing to a piece of 80 grit and held it nice and true while I spun the sandpaper, I did this little by little checking as I went.

I put this washer on the outer end of the suspension assembly/knuckle (between the A arm and knuckle)

 

[Gregorius]

I spaced my servo up and dont think its interfering with the body sitting flush but I will take a closer look and report back. I just looked up the specs and your servo is 44.9mm tall and mine is 38.7mm and I raised it 1.5mm so really 40.2mm

The metal plate aligns just fine if you rotate it 180* and then install it (though I may have gotten one from a bad run possibly) you can use it this way but the access holes in the plate wont line up with the parts inside. I guess the other possibility is that the hole pattern on the chassis was to blame and not the plate and that they fixed the issue mid run.

Its nice to hear that someone else is building this thing "thumbsup"

Did you also have excessive play (front to back) in the rear axles/suspension assemblies? Just curious, and I think I've found a good simple solution that I mentioned in the post above. I'll post up more details that I left out later tonight.

EDIT: I just checked the clearance I have on my steering servos to the main body bottom and its 5mm from the servo top to the bottom of the body. Measured from the top of the chassis rail they stick up 12mm above it. From the servo mount bracket (from the top) it measure 29.5mm to the top of the servo. One thing I've noticed about putting the body on is the motor wires are very tight and you need to bend them a bit and squeeze your way past them, could that be part of it?

Thanks for the feedback! My bad that I didn't take a closer look at the service cutouts - yes they are flipped:x Guess I'll postpone the mod until I need to service it...

I measured the servo also and it sits ~17mm above the rail and the body mount holes are missing each other about 2mm. I'm aware of the motor wire issue and I bent it in already. Guess a cutout is inevitable.

I too have the same play at the suspension arms. The front is somewhat mitigated when the steering links are connected, but the back ones are not so good, so I'll try out your idea later this week"thumbsup"

 

[HumboldtEF]

Thanks for the feedback Gregorius.


I put up a quick clip of the wobbly wheel before and after the fix/mod. I plan to put together a full video on this later but for now I'll leave this video unlisted


<iframe width="560" height="315" src="https://www.youtube.com/embed/2Fhh6QM89PQ" frameborder="0" allow="autoplay; encrypted-media" allowfullscreen></iframe>

https://www.youtube.com/watch?v=2Fhh6QM89PQ&feature=youtu.be

 

[whitrzac]

That looks like something some proper sized brass/steel tube would take care of.

Find one with the same ID as the pin and drill out the knuckle to fit the OD. Most hobby stores have an assortment of small/thin tubing.

 

[soze]

Thanks for documenting your build!

 

[Gregorius]

Thanks for the feedback Gregorius.


I put up a quick clip of the wobbly wheel before and after the fix/mod. I plan to put together a full video on this later but for now I'll leave this video unlisted


<iframe width="560" height="315" src="https://www.youtube.com/embed/2Fhh6QM89PQ" frameborder="0" allow="autoplay; encrypted-media" allowfullscreen></iframe>

https://www.youtube.com/watch?v=2Fhh6QM89PQ&feature=youtu.be

I was looking at the spare bag tonight and found a few pcs of spare thin brass washers so I gave it a shot. I added one at each arm and looks like to mitigate the play a lot (almost the same play as yours). I'm happy so far.

 

[HumboldtEF]

That looks like something some proper sized brass/steel tube would take care of.

Find one with the same ID as the pin and drill out the knuckle to fit the OD. Most hobby stores have an assortment of small/thin tubing.

Thats a great idea though that might only work on the inner portion of the A arms, the outer uses a M3 screw and not a pin. I did attempt to put one of the small shims in the inner pivot point and I was able to get it to fit along with the E clips but it ended up too tight with some resistance. So Finding some tubing to use there might be the best solution for these pins which are definitely in a slightly oversized hole.

I was looking at the spare bag tonight and found a few pcs of spare thin brass washers so I gave it a shot. I added one at each arm and looks like to mitigate the play a lot (almost the same play as yours). I'm happy so far.

I gave that a shot too, I only had 5-6 of them left and I found it might take 2 in each pivot to get it tight, so I'd need 16 for the rears alone. I just didnt have enough of them.
2 of these shims are very close to the same thickness as the washers I used.


I just checked and the shims look (as far as I can tell) to be 0.4mm thick and I think it could use 3 of them so 1.2mm (1 of them is from the stock setup) though when I measure the shim and washer combo I used its more like 1mm. I'll need to get one of these taken apart again and I'll test out some assorted shims I just rounded up, I suppose its a good excuse to do the front too.

 

[Natedog]

I spaced my servo up and dont think its interfering with the body sitting flush but I will take a closer look and report back.

Its nice to hear that someone else is building this thing "thumbsup"

Did you also have excessive play (front to back) in the rear axles/suspension assemblies? Just curious, and I think I've found a good simple solution that I mentioned in the post above. I'll post up more details that I left out later tonight.

Would be nice if deck height or whatever you want to call it was more standard on servos maybe? I've had similar problems many times, replace a servo and now linkage is wacked and sometimes not enough room, had to space them up and down few times too.



Yes, nice to see more of these builds!


Disappointing to see this kind of slop from the factory, great solution with shim washers (brass should be nicer against the aluminum arms). I would refrain from drilling any aluminum pivots oversize except as last resort, parts are probably not plentiful or cheap yet. This could be done for complete overhaul years down the line.



Nice way to thin the washers/shims by holding it still and spinning the sandpaper on a flat surface! I've always done figures 8's with the washer, but great alternative! Can't wait to see it painted. "thumbsup"

 

[HumboldtEF]

Would be nice if deck height or whatever you want to call it was more standard on servos maybe? I've had similar problems many times, replace a servo and now linkage is wacked and sometimes not enough room, had to space them up and down few times too.

That would be good for sure, I got pretty lucky I guess cause the only specs I looked at for these servos was the torque.



So on to the paint and things have slowed to a crawl :roll:

I took a bit of a break cause I worked my hands a bit too hard putting together the chassis and they needed a rest. But I'm back at it again chipping away at scuffing up all of the pieces of the body, which holy moly theres a lot to it.

Just some of the body parts

I went with Tamiya TS-70 Olive drab

I painted a few little bits so far

And these things which I have no clue what they are, anyone have any ideas? One goes up front on the passenger side and the other goes in the middle of the chassis driver side. I'm thinking air brake related maybe. sorry theres nothing close to judge scale but these are on the small side my guess is the real thing would be 1' in diameter and 2' long.

I forgot about this but the dash has lighting built in, the sticker alignment needs some work but its hard to notice when assembled.

And one thing thats really been making this hard (well not hard to do, hard to decide) is the main body needs to be painted before final assembly but also glued together afterwards so I'm still trying to figure out the best way to get it painted while leaving some areas clean for gluing (Acetone). I'm leaning towards masking off the area that needs gluing and plan on going back to touch up some areas. I considered just gluing it up and painting after but some areas will be pretty hard to spray and I foresee many runs with this method.

I think I'm at the point I can start with primer tonight. I know I can at least get to everything but the main body which might have to wait a bit longer.

 

[HumboldtEF]

I'm really not liking the single roof light so I'm gonna cut off the little mount and either bondo the hole or try to fuse in some scraps from the left over body parts sprue.

You can still see it in the shot above but I've working at sanding off the flash lines from the mold. cleanup has been fairly easy but I did need to work on the front end and roof a lot more than other areas




EDIT: ok I went for it and drilled some 3/16" holes which are the same size as the left over sprue that I used as a patch. I did start with smaller drill bits in order to get the hole located, I also cut down the mount a bit first with a fine toothed hand saw. I cut 99% of the way through the sprue with a razor before putting it in place to make it easier to cram in place, then I just snapped the rest off.

followed up by a coarse double bastard file

and working my way up to 320 grit sandpaper

Much better

 

[bent_hinge_pin]

I'm really not liking the single roof light so I'm gonna cut off the little mount and either bondo the hole or try to fuse in some scraps from the left over body parts sprue.

You can still see it in the shot above but I've working at sanding off the flash lines from the mold. cleanup has been fairly easy but I did need to work on the front end and roof a lot more than other areas




EDIT: ok I went for it and drilled some 3/16" holes which are the same size as the left over sprue that I used as a patch. I did start with smaller drill bits in order to get the hole located, I also cut down the mount a bit first with a fine toothed hand saw. I cut 99% of the way through the sprue with a razor before putting it in place to make it easier to cram in place, then I just snapped the rest off.

followed up by a coarse double bastard file

and working my way up to 320 grit sandpaper

Much better

Nice job!!!!!

Sent from my LGLS991 using Tapatalk

 

[OSRC]

Wow - this thing is awesome. Excellent build thread...can't wait to see it completed.