Peterbilt 6x6 Medium Hauler

[huber1918]

Awesome Build! Cannot wait to see the progress! Gives me some ideas for my Globe Liner.

[TRUCKMAKER]

Check out posts 42-44 in the link below to see what I did, if you look close you'll see that I took the lower rear case screw off the transmission. You will have clearance issues if you don't lift the trans mission which will be the case with any t-case you use. I'm not a fan of the Tamiya 3 spd due to its space sucking size, so this one is going away soon. You might also notice the spring pack on my steer axle . The extra height was in my favor but not so much in yours.

http://www.rctruckandconstruction.co...?t=9138&page=3

[scottyk]

That ride height addition is what turned me off from doing the 6x6 on my Mack build

Yours is looking very good! Nice work man

[Tommy R]

Originally Posted by huber1918

Awesome Build! Cannot wait to see the progress! Gives me some ideas for my Globe Liner.

Thanks!

Originally Posted by TRUCKMAKER

Check out posts 42-44 in the link below to see what I did, if you look close you'll see that I took the lower rear case screw off the transmission. You will have clearance issues if you don't lift the trans mission which will be the case with any t-case you use. I'm not a fan of the Tamiya 3 spd due to its space sucking size, so this one is going away soon. You might also notice the spring pack on my steer axle . The extra height was in my favor but not so much in yours.

http://www.rctruckandconstruction.co...?t=9138&page=3

I see what you mean about raising the tranny. Looks like clearance for the driveshaft would still be tight at full bump, but I won't be jumping this thing so maybe that's not a big deal. Ha! Do you have any more pics of how you put together your front suspension? Is that a TLT in there?

Originally Posted by scottyk

That ride height addition is what turned me off from doing the 6x6 on my Mack build

Yours is looking very good! Nice work man

Thanks! I'm trying to keep the ride height within reason, but fully expect it to be noticeably taller than a stocker. I'm thinking maybe 3/4" or so, but the Lesu tires may be taller which may raise it more. Not really sure how their diameters compare to the stock Tamiya tires.

[Tommy R]

Didn't have much time to mess with the truck until this evening and when I did I decided to focus on my gear reduction and transfer case solution. First things first I looked into how the tranny is going to interfere with a front driveshaft. Obviously, that's definitely got to be addressed!


I think I've narrowed down my drivetrain choices to these:
1. Use an Axial 2.6:1 trans as a transfer case and possibly a 2:1 planetary gear reduction in front of the Tamiya transmission.
2. Use a planetary gear reduction (probably 2:1) and add a t-case like the 2.18:1 RC4WD Disruptor or the 2:1 t-case from wtbcar.com:


In either of these solutions, the stock Tamiya tranny needs to be raised up fairly substantially....for two reasons. As mentioned, the tranny will prevent a driveshaft from reaching the front axle, but the 2:1 planetary will hit the steering/shifting servos because it'll push the motor forward. My best guess shows a height of 15-20mm is needed. Here's a rough approximation of the height required:


The floor will need to be trimmed, but I'm okay with that. I can always just build a simple cover for it so the trans is hidden from sight. My first estimation of where it'll need to be cut (everything within the white markings).


So before I order some standoffs I made some temporary 15mm spacers to see how that would work.


Driveshaft clearance should be okay with the trans raised 15mm, especially since the trans output will be fairly low.


Front view showing the height of the motor compared to the servo. It'll be reeeeally tight, but I can easily add a few more millimeters of spacers if need be.


Thinking this is what I'll need to cut away to accommodate the new trans height.


So now I need to decide what to do about the transfer case. I have an Axial trans so that's the cheapest solution. I'll just have to fab up a bracket for it. And it'll definitely get the outputs low enough to clear the stock trans. The wtbcar.com t-case looks like it would bolt in after drilling a couple holes so that'd be super easy, but it would cost me ~$50 and time to wait for shipping from (presumably) China. Not sure I'm patient enough to do that. Ha!

[Tommy R]

Axial transmission (all metal internals, of course) ready to be used for the new t-case. I just need to trim off the excess on the input shaft.

[TRUCKMAKER]

Did you give a thought to moving the motor transmission assembly forward? If it'll still clear the hood it would give you more room for the drive shaft and less material to remove from the floor. Doesn't look like you need to go up but a bit to clear the servo.

[Tommy R]

Ooh, good idea! Thanks! Here's a quick mock up keeping the trans at 15mm higher, but moved forward. Not sure how far forward I can go if I run a gear reduction like I was planning, but it would definitely safe some interior cutting!


As shown, it looks like it would protrude about half as far back into the interior.


What I also need to consider is where the speaker box will go. Don't most people run the speaker just behind the grill? If so, moving the trans up/forward will kill my space. I need to look into my options for speaker placement.

FYI, I don't know that I'll go with an MFU from Tamiya. While that would be great, I may opt to save some money and go with an alternative sound generator. As always I'm open to suggestions, but was most seriously considering this one:
https://www.aliexpress.com/store/pro...413729518.html

[TRUCKMAKER]

Speaker locations on these things are a personal thing depending on cab configuration and what all else you want to cram in there. One thing you need to watch when moving that tranny forward is where it is in relation to the front axle, ie so the axle itself doesn't get into the bottom of the tranny Isn't custom building these things fun

[Tommy R]

LOL! Yessir! I'm keeping the tranny just far enough back to prevent any unwanted contact.

Got the rear wheels in the mail today! Only issue is that I don't have a hex driver small enough to fit the nuts to secure the wheels to the hub. The Tamiya multi-tool is too short to reach down in there. I'm guessing it's a 4mm or 4.5mm hex? Anyone know for sure? FYI, these are Lesu wheels.

[blitzk]

Hey Tommy R, I bought these sound units before and they look the same but a bit cheaper if you are interested.http://www.rcbrmin.com/index.php?mai...roducts_id=786

[Tommy R]

Originally Posted by blitzk

Hey Tommy R, I bought these sound units before and they look the same but a bit cheaper if you are interested.http://www.rcbrmin.com/index.php?mai...roducts_id=786

Thank you for that! I see it says not to use a LiPo, though. What kind of battery do you run?

[Tommy R]

So whichever transfer case I end up with, I'm pretty sure I'm going to need a gear reduction. Using an Axial trans/t-case and a 2:1 gear reduction unit (GRU) would get me to 5.2:1 reduction over a stock setup. That's pretty darn low, but not sure if it'd be TOO low. However, I can't locate any 2:1 GRUs. Closest I can find is a 3:1 unit. It's cheap so I went ahead and ordered it.


Doesn't look to add much length to the motor.


Now I'm thinking the Axial t-case may be too low so I may consider a unit with a little taller ratio like 2:1. I have several options. I'm open to suggestions from those of you who've geared down your trucks. Knowing I plan to take this thing offroad and pull reasonably heavy loads with it, what kind of overall gear reduction should I look for? 3:1? 5:1? 7:1?

[TRUCKMAKER]

Im running a 55T through the Tamiya 3 spd into the Axial trans as my my t-case no other reduction. Plenty of climbing power loaded, empty in sand dirt whatever, works fine.

[Tommy R]

That's great to know, thanks! I guess the next order of business is to relocate the motor/tranny and then figure out the t-case placement. I'll also have to start looking into driveshaft options.

[TRUCKMAKER]

Check this out:

http://www.rctruckandconstruction.co...read.php?t=708

I use K&S brass tube which is an easier fit than the aluminum tube, but the rest is the same.

[Tommy R]

Ooh, great idea! Today I had to go to the hobby store to get a 4mm hex driver so while I was there I picked up some 1/2" brass tube. Look forward to trying it out!

Speaking of that hex driver, it allowed me to finally put together my new rear wheels Love 'em!

[blitzk]

I've just been using a Nicd 7.2v battery pack so far on the one truck I have it installed in.
Next time I get home, I will try a Lipo on it and let you know. Probably won't be home for about a month, though.

[Tommy R]

Originally Posted by blitzk

I've just been using a Nicd 7.2v battery pack so far on the one truck I have it installed in.
Next time I get home, I will try a Lipo on it and let you know. Probably won't be home for about a month, though.

That could be an issue for me because all I've run for years are LiPos. No more NiCd or NiMH for me. Worst case I suppose I could run a LiPo through a voltage converter to drop the voltage to an acceptable level for the sound module, but it'd be nice if that wasn't necessary.

On a side note, my Shapeways front fenders shipped today! Can't wait to see how they look. I guess it's time to do some more bodywork.....

[Tommy R]

Since the fenders are on the way, I decided that I may as well start on the one thing that I've been dreading......bodywork. I'm okay with styrene, but it's been awhile since I've done any detail work with the stuff. And in an effort to make it as easy as possible to replace the hood sides I wanted nice, square cuts and edges. Eventually, I decided to just jump on in and make it happen.

I decided to remove the fenders first to make it easier to cut by the cowl area. First I outlined the cut areas with a thin Sharpie marker. Then I used string to cut through the fenders and removed them.


Next I measured the styrene of the body to be .060" (1.5mm) thick so I used my calipers and scribed a line at the .060" mark. Applying black ink beforehand made it easier to see. Then I used the string method to cut along the line as carefully as I could. Came out rather clean! That's encouraging!


Now with the fenders removed I was able to use my razor saw to get nice, straight lines along the cowl and the horizontal line near the top of the hood. Using a combination of sawing with the saw and scoring with the Xacto blade, I was eventually able to cut the sides out. Honestly, it went quite a bit smoother than I expected.


They look nice and square to me! Mocking up an uncut piece of styrene confirmed my suspicion: nice and square. Good stuff!


An update on other components....

The front wheels and all the tires should arrive to the States any day now. The posts to raise the motor/trans will be here Saturday along with a bunch of hardware in my goal to replace as much Philips head hardware as possible! And I was able to cancel my order for the 3:1 reduction unit. Sweet!

I've got to pack for a camping/offroading trip this weekend so time is tight, but if I get some time I may try to bond the new, uncut hood sides to the KH. It still has a long way to go, but progress is progress!