Crawltima?

[Returning_Jim]

This is a work in progress.

I had a silly idea to put crawler wheels and tires on my Ultima. I converted the front end to have hexes using Lazer and RB5 parts, and have installed GMade wheels and some 1.9 crawler tires off of Ebay ($12 shipped for the set, and I was suprised at the quality and soft rubber compound). I need to find some tall shock mounts and buy long shocks, amongst other things...Anyways, I thought it looked kinda cool.

[GoMachV]

We already have a DennisM here but I'm digging the look and you beat him to it so kudos!

[DennisM]

It´s a Beast

[j0pp3]

As a crawler enthusiast I like your work but you'll need a more crawler related motor with extreme torque to handle the stock gearing. At least an 80T crawler motor or even more turns. A crawler should be able to handle really low speeds without stalling or getting hot. Otherwise it will perform more like a Rock Racer or a Mud Truck.

Those rims are great. I think I have twelve of them. A set for 4x4 and a set for an 8x8-project

Remember that you can use shock towers from the Ultima Outlaw model to use longer shocks.

[Mr. ED]

For the rear you might be done by just using the matching gold shocks but mounting them on the innermost hole on the arm.

I have a similar creation in my shelves but haven't run it yet: never got around finishing it as all my electronics reside in more race oriented projects.

For the moter: I' thought of using an outrunner moter with 5mm axle and fitting pinion in 32dp. The one I have is 540 sized and has less than 800KV with loads of torque.
That should be perfect I think?

[SFC K]

I like the look of it with those wheels. It looks killer! It will make a better trail rig than a crawler with only the rear wheel drive though.

For lengthening the shock mounts, you could get some carbon fiber and cut out some strips and attach them to the current shock towers to extend them.

[Returning_Jim]

Yeah, I didn't intend for this to actually be a crawler. I just liked the look. Part of my motivation was to have taller tires which would enable me to drive in grass more easily.

Most of you have probably seen this, and maybe this guy is on the forum already, but here's where I learned how to convert the front end to hex drives:

http://fun-with-rc.blogspot.com/2011/11/turbo-ultima-front-end-and-wheeltire.html

[Returning_Jim]

What size pinion do you guys think I should run with these tires? The tires are 108mm. I have a 12T pinion on order but I'm thinking it may not be small enough.

[Mr. ED]

No straight answer for that question: really depends on what type of terrain you're going to run it on and what motor you'll use.
Assuming you are using 7.4v lipos and brushless motors I think the 12 teeth pinion will be ok with a 17.5T.

(Just a gut feeling though: I used to run my ultima with stadium truck tires but didn't have brushless, no lipo... Also had 0.6mod spurs and pinions actually , so, really hard to compare)

[Coelacanth]

What size pinion do you guys think I should run with these tires? The tires are 108mm. I have a 12T pinion on order but I'm thinking it may not be small enough.

I could probably help you calculate a "best guess" starting point pinion gear, but I'll need the Ultima's gearbox gear ratio and the diameter of your tires. Is the Ulty's gear ratio the same as the Optima? I created my own Rollout Ratio Calculator in Excel that should get you to within 10% of your theoretical optimal ratio.

EDIT: I just noticed you had your tire diameter. I'll punch some numbers and reply in a bit.

Re: the long shocks, you might be able to do as Mr. ED said and use the inner-most hole, plus you can also install 4.8mm ball studs and 4.8mm long-length ball-cups. Kyosho makes some pretty long hard ball-cups (they're a grey color, not black) that will add at least a centimeter to the shock length. I used those on my Barney build.

[Coelacanth]

What size pinion do you guys think I should run with these tires? The tires are 108mm. I have a 12T pinion on order but I'm thinking it may not be small enough.

How many teeth is the Ultima spur gear?

EDIT: Nvm...looks like 41T. If that's incorrect or you're using an aftermarket spur gear, let me know.

[Coelacanth]

Okay, sorry to be triple-posting...it appears that the Ultima has the same gear ratio as the Optima, 3.03:1, and the same stock spur gear, 41T. So factoring in the extra height in your tires, to have a rollout ratio comparable to stock--all else being equal, you could try either a 9 or 10T pinion gear. Either of those should put your rollout within 0.9 and 1.1".

[Returning_Jim]

Hey thanks for helping me out with that. Looks like I need to order another pinion.

I'm still trying to decide on how this thing will be powered, but one thing I'd like to do, is to mount a shorty pack longitudinally so that the battery isn't sticking out the sides.

[Coelacanth]

Pick up both a 9T and 10T, maybe even an 11T, just to have all your bases covered. Pinions are cheap and usually available locally. For a crawler--and this is certainly not my area of expertise--you'll want a motor with high number of turns, like the other guys said...and probably I'd go so far as to suggest a sensored brushless setup, as unsensored setups sometimes suffer from cogging at low speeds. You shouldn't have that problem with a sensored motor & ESC.

[Kyoshojoe]

Looks sweet, kinda like a smaller version of the modern ultima db.

Be wary of larger tires and torque. The Ultima center gear is not very strong and there is no slipper set up. Those gears arent cheap either.

You just put a tire twice as tall as intended and with super grippy tires so if you put a hot motor in you might start breaking things. I ran an ultima with blackfoot tires and wheels back in the day and if the center gear didn't strip a few teeth the dogbones or wheel shafts would snap. Its not the spur section of the center gear that usually goes but rather the smaller secondary gear.