PTI Project Crawler

[pbarsamian]

Backstory:
I bought an original PTI Goliath kit and built it strictly as a backyard basher w/ 4ws and a 17 turn motor. After coming up w/ a few mods and doing some nice CNC carbon and alu parts for it, I got bored and set it aside while other car interests took hold. After a recent failed attempt to sell it on ebay, it seemed doomed for the moving box pile to collect dust. I received a Losi Micro Crawler for xmas from wife and became so enthralled with crawling I joined this forum and decided to do a project crawler by making and or using stuff I had, the PTI finds new life!. To clarify, I have a reasonably equipped CNC and manual machine shop in my garage which has become my ultimate lego set.

Mods to date:
1. turned all new alu suspension links for front/rear, 3.4" for top and 4.4" for bottom w/ 4-40 rod ends (steel threaded inserts) and the stock ball links.
2. after trying unsuccessfully to use Revo drive shafts, I turned custom steel drive shaft extenders with tapers and 3mm set screws, chopped and filed the stock CVDs, and effectively extended the stock driveline.
3. I opened the axles and locked the diffs by removing the balls washers and tension screw setup, drilled and tapped set screws on each out drive to lock to stock bevel gear, and put a 2.5mm screw thru center to lock the whole unit together.
4. Designed and CNC cut all new alum and CF servo mounts to move servo up onto axles, the alu mounts also double as shock bottom mount points to allow elimination of the cam suspension setup.
5. I had to drill and tap new 3mm holes to move the stock shocks out for direct link to axles
6. CNC cut new CF top plates to simplify layout and allow shock clearance
7. replaced XRS esc and 17 turn motor with a super rooster I had and a new 85turn Integy V11 crawler motor.
8. bored out a set of 2.2 hex nuts I had from another buggy in my spares bin, added proline chisels on their rock crawler 2.2 rims with 3oz of stick lead wrapped on each inner rim
9. cnc turned 4 alu body posts from a design I'd already done for a heli project, the spacing happened to be perfect and they were designed for 3mm screws.

pics below:



Next Steps:
1. change out stock shocks for tmax metal ones w/50 wt oil
2. finish painting proline crowd pleaser crawler body
3. lighting system

Possibilities:
1. turn new alu out drives with tapped screw holes for locking diffs
2. design custom gearbox and cut from ALU or purchase RC4WD one
3. (likely) design and CNC cut custom CF sideframes to allow updated gearing and reposition upper shock mounting w/ added tuning mount holes
4. CNC cut custom alu HD lower bent links from 0.25" 6061 flat stock
5. convert to brushless crawler power system or replace current super rooster with a goat controller.



http://www.photoshop.com/accounts/5e...3237fa3b9200fa
http://www.photoshop.com/accounts/5e...210ac253052ef4
http://www.photoshop.com/accounts/5e...37ded284dbc5d9
http://www.photoshop.com/accounts/5e...e21be82ae62a76
http://www.photoshop.com/accounts/5e...4d1d7500bae26f

[rik]

YES!!!!!!!! A new PTI Thread!!! Very nice and very clean rig man! i got one as well....bought it before the rtr's and the extension kits and all that. had to do it all myself. cad it, machine it, and test fit it...still a work in progress four yrs. later... lucky you, i didnt see this rig on flea-bay or you wouldnt have it any more. LOL.. keep up the good work and keep us posted! we on the pti forum are lonely!!!!

[76 warlock]

I agree nice and clean rig. Lucky you to have all those toys in your garage!

[pbarsamian]

Thanks guys.

I am going to ask for help/advice:

I'm not getting anywhere near the kind of torque I thought I would get to the wheels on this thing. I've tried a couple of different 2 cell Lipos but I can't seem to get it strong enough to really pull the front end up over stuff for hard climbs. My suspicion is that it is gear ratio, (using 12t/81t combo) but with an 85 turn motor, I expected to get some really strong wheel spin to get the front end up. The behavior I see (for example) is that if I pull up to a vertical wall (maybe 6 inches high) rolling straight up to it, it will stall the front wheels pretty easily even though I have good traction on front/rear.
I was thinking of going brushless but can't imagine that will just simply solve it.

I've been contemplating building my own gear reduction setup given I have the stuff to make it but I'm a bit at a loss as to the anemic power. I measured the stall current and it's only pulling about 9.5 amps.

[pbarsamian]

So I went to stock drive products and priced out some gears to see how much cost would be involved in making a gear reducer for this current drive train, I found:

303 Steel Pinion Shaft with 48p 10t pinion gear cut into it (.25" shaft)
303 Steel Spur gear with set screw hub (.25" bore) 30 tooth.

Total is 31 dollars for both. I'd then need to machine two new alum motor mount brackets similar to the old one (one for each side), get bearings, cut the pinion shaft to length, bore it for a support screw on the other end, and fit together.

I'm thinking it's probably better on the time/value of money front to get an R2 tranny and do a new set of CF sideframes to fit it and the rest of the stuff (at 60 bucks the gear box is done already).

Thoughts?

[jwo]

you could use a wheely king gru. you can find them on tower. little modifying of the chassis plates to fit. i used this reduction with a 35 turn motor and 87t axial spur , 14t pinion. it was a bit slow though, but it had tons of torque. this should give you plenty of torque for only 20 bucks. you will have to brace your motor plate as well so you dont chew up spurs.the stock tranny doesnt have the gearing at all for crawling. hope this info helps. ill be watching this build.

[jwo]

heres a thread that shows one in the chassis. i did a little digging for you. mine still has the same setup, but its no where near stock form so you wouldnt be able to see how it fits it the chassis. anyways there is a pic probably about half way down the thread.Gear reduction

[pbarsamian]

Originally Posted by jwo

heres a thread that shows one in the chassis. i did a little digging for you. mine still has the same setup, but its no where near stock form so you wouldnt be able to see how it fits it the chassis. anyways there is a pic probably about half way down the thread.Gear reduction

You rock dude. Nice find, this is EXACTLY what I was looking for, I can totally work with this.

Tower order placed....

[jwo]

Originally Posted by pbarsamian

You rock dude. Nice find, this is EXACTLY what I was looking for, I can totally work with this.

Tower order placed....

hey, glad to help. its a very good gru. i am still using mine. i have had mine for a year or two. still works perfect. there are others, but you cant beat that gru for the price.plus it doesn't take much to fit it in there.only down side is that it will raise the motor a bit. i cant take the credit for it. some one on here is the founder of this part for the Goliath. just trying to help ya out. little money saved is more money for other stuff. not sure what motor you plan on using but like i said i have a 35 turn with the stock axial spur(87) and a 14t pinion. top speed was 2 or 3 mph if that. i know these are suppose to be slow, but you do need some wheel speed. never the less. you wont be disappointed with the gru.

[pbarsamian]

Originally Posted by jwo

hey, glad to help. its a very good gru. i am still using mine. i have had mine for a year or two. still works perfect. there are others, but you cant beat that gru for the price.plus it doesn't take much to fit it in there.only down side is that it will raise the motor a bit. i cant take the credit for it. some one on here is the founder of this part for the Goliath. just trying to help ya out. little money saved is more money for other stuff. not sure what motor you plan on using but like i said i have a 35 turn with the stock axial spur(87) and a 14t pinion. top speed was 2 or 3 mph if that. i know these are suppose to be slow, but you do need some wheel speed. never the less. you wont be disappointed with the gru.

Thanks, I think my plan is to try a couple of spurs, I have a bunch from a 4wd buggy that are exactly the same going down to about 60 teeth, (I have an 80 tooth handy and some 84s on order I'll try) and I have some larger 48pitch pinions I'm going to try. Also ordered the Novak Rooster crawler setup with the 55t motor, may try that motor and some combination as well.

Meanwhile I got impatient and tried my 17 turn motor in this just to compare motor torque and of course shredded the plastic diff outdrives in the front.

Current project is that I'm manually turning custom mild steel spools that will work with the stock diff gear (with some mods to the gear). I'll post pictures of it when done.

[jwo]

with my 87t spur i had to trim the tranny plate on the bottom a bit for clearance. my spools that held the diff gear were metal locked ones. but when i got mine it was the crawler kit. not exactly sure, but there may be some locked spools some where in the forum that drop right in, unless you want to make your own of course. ill keep checkin in on the progress.i dont know about you but i prefer to build something myself then just buy it. if i cant make it, then i buy it. nice to see a pti build. keep up the good work.

[pbarsamian]

Originally Posted by jwo

with my 87t spur i had to trim the tranny plate on the bottom a bit for clearance. my spools that held the diff gear were metal locked ones. but when i got mine it was the crawler kit. not exactly sure, but there may be some locked spools some where in the forum that drop right in, unless you want to make your own of course. ill keep checkin in on the progress.i dont know about you but i prefer to build something myself then just buy it. if i cant make it, then i buy it. nice to see a pti build. keep up the good work.

Totally agree, rather build meself, but with newborn twins, it's getting harder and harder to get into the shop to do stuff.

I have the material and made my mistakes on the one I tried to make last night, I'll see what I can get out and do today if anything...

[pbarsamian]

What a pain to turn these down! This cold roll from Lowes is really annoying to turn, it's like the worst combination of soft steel and not quite round stock, but I finally finished them. I didn't spend a lot of time on the surface finish since they're hidden in the axels anyhow just got it smooth enough on the bearing mount surfaces:

http://www.photoshop.com/accounts/5e...718bf3e8330aed

http://www.photoshop.com/accounts/5e...8f064e88b543b6

The gear center hole was bored out with a 25/64ths drill (to accomodate the the spool going through it) and the rest was done with a lathe and mill to slot the out drive cups.

The gear is held on with two 2mm screws that hold the gear in tapped holes to the spool.

[pbarsamian]

So after messing with the suspension and mounting the Traxxas shocks, I decided I needed more shock mounting options, drawing up a carbon shock mount to put on the ends of the chassis, pics to follow soon....

[pbarsamian]

Thought I'd post a couple of shop pics...

http://www.photoshop.com/accounts/5e...11f69649047ed7

http://www.photoshop.com/accounts/5e...aaf779a8cea882

http://www.photoshop.com/accounts/5e...499cee96aeae0c

They don't show my new 12x36 lathe....

[jwo]

Originally Posted by pbarsamian

What a pain to turn these down! This cold roll from Lowes is really annoying to turn, it's like the worst combination of soft steel and not quite round stock, but I finally finished them. I didn't spend a lot of time on the surface finish since they're hidden in the axels anyhow just got it smooth enough on the bearing mount surfaces:

http://www.photoshop.com/accounts/5e...718bf3e8330aed

http://www.photoshop.com/accounts/5e...8f064e88b543b6

The gear center hole was bored out with a 25/64ths drill (to accomodate the the spool going through it) and the rest was done with a lathe and mill to slot the out drive cups.

The gear is held on with two 2mm screws that hold the gear in tapped holes to the spool.

those spools came out nice. dont look much different from the stockers. good job and a very nice shop you have.

[pbarsamian]

So after looking at the design a bit more, I've convinced myself that shock extensions to get them a bit more upright is just a temp fix. I'm in the process now of completely redesigning a set of carbon side frames and will be doing new a new pair of spur gear/motor mount pieces out of .25" alu. I'm going to widen the chassis .5" overall (I have 2.5" flat stock handy) and am going to offset the spur slightly (using a smaller spur like 60-70 tooth) and see if I can't get the motor and WK GRU mounted a bit lower in the frames. I'll try to post drawings when I get them done.

Any gear ratio (overall) suggestions on a 55t Novak?

Also public thanks to Josh who very generously offered to send some spare parts to help this build...

[jwo]

yeah you can only do so much with the stock chassis. i did the same thing with the shock mount brackets. after doing what i could with the stock chassis i built a tuber for it. i flipped the tranny right on its side for the tuber in my best attempts to lower the cog. worked pretty good. lowered it alot.much more stable. i still used my 87t spur. the down side was that my maxx shafts would hit the motor when flexed in one direction about 3/4's of the way through its articulation. never bothered me anyways.there are other ways around it though. i still use the pti tranny and reduction in another rig i built setup a little different to get around it.ill see if i can post a pic of it for ya. as for the spur size i couldnt tell you. thats all i can say is i ran a cheap 15t tazer for an esc with my setup and the drag brake from the reduction was more then enough to hold it on any incline. i can def tell you if you ran anything close to what i ran its gonna creep with a 55t my buddies axial with a 55t and a rooster could out run it easily on a 6cell.

[pbarsamian]

Thanks for the thoughts on gearing Josh.

Does anyone happen to know what the total gear ratio of the Axial machine is (to the wheels)?

[pbarsamian]

Carbon concept frames mostly completed and mounted, I still need to cut two cross member plates and turn two alu spacers for this but the pic below should give an idea. It now has LOTS of shock setup options.

These fit the stock gearbox but will also accomodate the alu gearbox sides I'm working on to better support the WK GRU I have on the way...

http://www.photoshop.com/accounts/5e...30e6c56e1305aa