Crawltima?

[Coelacanth]

Typically, crawler motors have much lower RPM than buggy motors; at 35T it's down to 12,000 or less RPM, and gets lower and lower the more turns it has. The idea is to have high torque but low spin speed. Hot buggy motors can easily exceed 30,000 RPM, which creates the need for a slipper gear, if all those RPM come too much all at once. If the O.P. is really going the crawler direction and not the racer direction, a slipper gear becomes less and less of a need, I would imagine.

[Returning_Jim]

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.

I wonder if the Outlaw Ultima truck was known for drive-train failures in the old days. I don't remember it having any special parts in the gearbox aside from a different pinion.

[Coelacanth]

The Ultima Outlaw truck was really just a buggy with Kydex body mounts, plastic bumpers & roll bars and a Lexan truck body. However, you could mount Tamiya monster truck-style wheels & tires using special axle extenders & wheel adapters, but without changing the pinion/spur ratio to accommodate the much larger tire diameter, you'd almost certainly run into overheating issues. Crawling and speed are opposite ends of the spectrum so you'll need to select the right motor for your application.

[Returning_Jim]

I don't intend for it to be a crawler, I just thought "Crawltima" had a nice ring.

Basically, I just think it looks cool with these wheels and tires, and I'd like to be able to drive in freshly-mowed grass.

I just ordered a 10t pinion, so we'll see how that works.

[Coelacanth]

What are your plans for a motor? I'd think something between a 13.5T and a 10T would be good, and you can dial down the punch if necessary. Running tall, heavy tires means the motor will need to work a bit harder to spin them, which you'll be freeing the stress up a bit by down-sizing the pinion to a 9T or 10T. I'm interested to see how it runs, hopefully you'll record a vid!

[Kyoshojoe]

I don't intend for it to be a crawler, I just thought "Crawltima" had a nice ring.

Basically, I just think it looks cool with these wheels and tires, and I'd like to be able to drive in freshly-mowed grass.

I just ordered a 10t pinion, so we'll see how that works.

The name is cool and does have a nice ring to it. I think you will be fine for mild running and normal use, the ultima is pretty stout and time proven but like anything has its weak points and one is better off with prior knowledge of such issues rather than finding out the hard way, especially with vintage equipment that is rare and expensive. You just have to respect it and be carefull.

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.

You might want to check out my build thread for ideas on battery placement and other ideas as well.
http://www.rc10talk.com/viewtopic.php?f=30&t=37070

[Diggley]

I like it!

[Returning_Jim]

As explained in this thread, I'm using a 19T 32p pinion gear for a 5mm shaft for the final pinion gear inside the gearbox:

http://www.rc10talk.com/viewtopic.php?f=30&t=37626

This is the one I bought and it turned out to be perfect. From "Hot Racing:"



The teeth are wide and almost match the width of the teeth on the diff. Also, I like how it is hollowed out inside for less rotational inertia. This thing ended up fitting so perfectly, that this company could sell these as "Ultima/Optima metal final pinions" and no one would question it. I strongly recommend picking one of these up. I paid $9 with shipping, which is a heck of a lot better than $35-45 for the Option House part.





I haven't put this into the "Crawltima" yet, but I fully assembled a gearbox from extra parts to make sure there were no issues before tearing into the "Crawltima," and everything fit great. I'm super stoked on this part!

[GoMachV]

Looks like grandpa Jones approves

[Returning_Jim]

How could he not?

[Returning_Jim]

Oh, I forgot to mention that I've installed a 10t pinion as well. It doesn't look like the motor can swing any further forwards, so 10t seems to be the lower tooth limit without breaking out the dremel.

[Returning_Jim]

Well, something disappointing happened.

I went to dink around with the Crawltima some more and noticed that both of the front wheels had self-distructed in the following manner (this car has not been run yet):





I assembled all four wheels the same way, and the rears don't show any signs of trouble. I have to assume that the front pair, which had been packaged together, came from a bad batch of plastic or something. There's no reason that the clamping of the tire beads should cause this. I don't know that I want to spend another $20 on a pair of these since I'll be constantly wondering if this is going to happen again...

So for now, I've gone a different direction. I had an extra set of Optima wheels sitting around, so I decided to slap them on. I liked the scale looks of the RC4WD ones, but these are cool too.

[Coelacanth]

10T would actually be your theoretical ideal pinion gear; how are the motor & ESC temps bashing that beast around with those tall tires? I assume there are no issues with that gearing for those tires?

[Returning_Jim]

I haven't run it yet. I'm trying to find some turnbuckles and rear shocks.

Anyone know where to buy turnbuckles in various lengths?

[Returning_Jim]

BTW, a bit of Comet powder on a wet washcloth works pretty great to get old Optima wheels white again.