OFNA Ultra GTP / MBX conversion
 

So I had a MBX buggy sitting around, and decided to convert it to a GTP on road car. It was not much good as a buggy, so I figured that it would do better as a road car.

Purchased a new front bumper and body mounts for the gtp, fit great, as the mbx and gtp share the same chassis, etc. I made an L shaped mount for the KB45 10l out of some 6061 al angle. Bolted it to the rear center diff bulkhead, and left enough of the L portion to screw it to some existing chassis holes. I also reused the upper rear brace I made for the buggy, and mounted the ccbec and the mm to it. Center diff was replaced with a solid center drive with the 51t plastic ofna spur gear (all stock gtp dirt oval parts).

Battery tray is designed to hold a pair of 2s2p emoil (drill lipo) cells. I have my trakpower lipos in there in the pics, artfully taped to fit the tray as it is too long for them. The emoli cells did not seem to have the punch and top speed of the trakpower lipos, despite being 6000mah. They must have a lower c rating, probably more like 15c.

Pinion is a 20t, got it from sdp-si. It is mod1 and has a 6mm hole, so I did not have to mod the KB motor shaft. Nicely made pinion, not hardened though, so it is only good for plastic spurs.

Only compaints so far is that the shocks have too much travel. A true gtp has shorter shocks, and I have a spare set of revo shocks, so I may have to make them work. The extra travel causes the body to catch the ground under hard braking and cornering. I was going to limit the travel of the stock shocks, but I figured that the revo shocks would be about the right length. Plus the stock shocks are crappy.

If someone else with a GTP (Briang?) could measure the length of the shocks at full extension it would be a great help.

Now for the pics!

http://i206.photobucket.com/albums/b...p/DSCF1926.jpg
http://i206.photobucket.com/albums/b...p/DSCF1927.jpg
http://i206.photobucket.com/albums/b...p/DSCF1928.jpg
http://i206.photobucket.com/albums/b...p/DSCF1929.jpg

Looking good - Are you able to lay the shocks flatter and stiffer to get less vertical travel....

LMK if you see any reasonable GTP bodies best i've seen is 48 for a porche or 45 for a viper - Could you also measure the hub to hub distances (W/L) I'd like to see how far off the mugen is... thanks

How are you liking your solid center shaft? I love mine and how it made my truck drive better.

I found my body on ebay for 15 bucks shipped. Not sure how many are floating around though. Have you looked on tower hobbies yet?

I like the solid center in this car, and oanything on road, but prefer a diff with thick fluid in my 1/8 buggies, and the revo. I find that it helps the steering feel and overall turning ability. I like to drift and goof off with my on road cars.

Looked on ebay nothing doing atm - tower is 50+

I'm 14.5" length between hub centres and just under 11.5" width to edge of hub hex.

How does that compare...

Thanks

Just gotta find a tape measure at work tomorrow and see what it specs out at.

Check these specs: http://www3.towerhobbies.com/cgi-bin...?&I=LXTCJ1&P=7

Really nice and clean build , that centre shaft what a wonderfull idea . How does it pull with that KB . internaly they are the same size as the 22xx series lehners just not as efficient

I am very happy with the kb so far. I have put about 2.5 packs thru it, and everything seems to be staying cool. It has quite a bit of power, and cand draw the batteries pretty hard at full throttle. I have the punch control set at 20%, and may move it back up to 50% for less wheel spin out of the hole!

The solid center gives it a different feel to a buggy, but I am used to it from driving shaft drive 10th scale cars. Still prefer the diff in a buggy, but it is cool drifing this big car around the parking lot!

The mm seems to be ok with this setup. I had a novak cap on the mm, but it fell off. I could not get solder to stick to the joints on the board, so I will attach it to the input leads near the board. The esc ran noticably cooler with the extra cap. I may also put a fan on it, as I have a few 12v units hanging around.

On a side note, what would it take to have the fan temperature controlled? Have some sort of sensor on the heatsink, and a relay or solid state elec. to switch it on and off when needed? Maybe BrianG could whip me up something, given his electrical genius background?!

"electrical genuis background"??? lol, yeah right! Just a hobbyist...

Anyway, to make one out of discrete components would be fairly easy:

Maybe a Schmitt trigger (op-amp or comparator based), with a thermistor v-divider on one side and a fixed 5v regulator as a reference on the other. Drive a small NPN transistor configured as a switch to turn on the fan.

Or, see if you can find an all-in-one thermal switch IC. Most of the ones I know of are thermally controlled fan speed controllers, not on/off controllers.

Hmm, the thermally controlled fan speed thingy sounds interesting.

If it would be "fairly easy" to build, do you want to make me one? Funding will not be a problem.

How big do you think it would be? Size of a bec, or larger, like a house brick?

Here you go : http://search.digikey.com/scripts/Dk...eywords=switch

If I built it, it would probably be fairly large, like the KoolFlight BEC - maybe a tad smaller. Much easier to use one of the devices Arct1k linked to (except weed out normally-closed models): http://search.digikey.com/scripts/Dk...ormally%20open

A fan speed controller is unnecessary IMO. It's not like you are trying to maintain a specific set temperature, but rather just keep it cool. And TBH, just an inline manual SPST switch to the fan would be adequate and simpler.

Are you using flux when you solder? I realize that some solders are rosin core and don't necasarily need more flux but I always use it and it makes the solder flow right away and makes a very strong bond.

Interesting experiment but why not let the fan run - Can't use many amps...

This is true, just would be nice to keep the esc at some sort of temp, must work best at a specific temperature?!

Maybe the cooler the better!

Generally elecs run better cooler - just look at pc's - liquid nitrogen required for fastest clocks...

PS linc anyway you could mock up what a body would look like with those dimensions at some point - cheers

The 11.5 width will be ok, my mbx is right at 12 inches wide at the end of the hexes.

Now the wheelbase is 12.5 inches and the viper body fits perfectly.

Heres a few pics, the wheelbase shot has the body of the tape measure right at the 14.5 inch mark. I did not bother with the width as it was almost identical.

http://i206.photobucket.com/albums/b...p/DSCF1930.jpg
http://i206.photobucket.com/albums/b...p/DSCF1931.jpg

Many thanks - Looks like i may struggle with the body - I think I might get some buggy slicks or road rages and see how it performs...

If it is fun I can then go for the bumper setup and look at a body...

You will have fun with it, the longer shocks do make more exaggerated motion of the chassis, but it will not matter without a body that is close to the ground.

Which to go for:

- http://www.rcuniverse.com/market/item.cfm?itemId=377392
- http://www3.towerhobbies.com/cgi-bin...&I=LXMW85&P=ML

or any other suggestions?

road rages suck. No traction at all. The slick you listed I have no idea. But there is an ebay seller that sells slicks that lookmlike that and are terible. Cheap.... but terible.


The Ofna Belted tires (slicks and street treads) are awesome, but a little more $. I personally like the street treads the best of all street tires I have tried. Belted for no balooning from the factory so they handle awesome and they also have great traction.
http://www3.towerhobbies.com/cgi-bin...?&I=LXJAT0&P=7
http://www3.towerhobbies.com/cgi-bin...?&I=LXJAS9&P=7


The GRP Rally tires were great too IMO, but it appears that they have been discontinued. :grrrrrr: That sucks. I used them all the time for parking lot oval. They were a great mix of traction an wear life.
http://www3.towerhobbies.com/cgi-bin...?&I=LXMXB8&P=7


I have a set of these that are ok. Espescially for the cost $31 for a set of 4 mounted. But the sidewall is a little taller so they are not as precise feeling as the lower sidewall tires I listed above. http://www.amainhobbies.com/product_...ducts_id/17912

Thanks for the tip on road rages and the cheapo ones - no point wasting $30...

Has anyone tried these?

http://www.gohobbies.com/itemINT-C22685.html

http://www.advantagehobby.com/produc...cat=517&page=7

Is the later the same just not "belted" assuming like taped to slot balooning?

The first pair would be good for drifting.

I have used road rages, the 2.2 versions and they were ok, most likely work better on a heavier vehicle that is 4wd.

Yea the Ofna ones are good. they are the same as the belted ones rubber wise, just not belted. They handle pretty well as long as you keep it under 50 mph or so. If you plan on running faster regularly I would recomend the belted. These are the ones that came stock on the DM1. They were good.

Cant comment on the integy. Never seen them before.

What are you gonna be using them for? General street bashing?

Well probably - I was going to put them on my stretched MBX5 for a few runs... If I like it i was going to make it GTP like... Put on the foam bumper and buy a body...

We'll see... I hear that near me they run some GTP's

Linc- am I missing something, or are you running that big kb45 on only 2s? Hows that work?

Nope, using a pair of trakpowers in series for 4s.

hi guys just doing a ftx street racer as it called here in the uk we race them on a large oval nitro at the moment but here is a pic of the first convertion

couple of body pics and the raceway

Nice Conversion! :yes:

I'm getting VERY curious about those kb45's!

Just a thought here Linc.

Still got that container of 10w-30 sitting around?

Couldn't you heat that pinion up and harden it by quenching in the oil?

the tires on rcu look just like the ones that came with my yusa rally, so i would look elsewhere.

I actually found out that the ability to harden steel depends on the type of steel. Not all steels can be hardened. Some of the pinions can be hardened and work fine. Others may not work so well.

I can safely say that the KB45 10L I have runns cooler than a similar geared 7xl. Now I am not sure if a feigao 9xl (similar kv) would be able to pull the gearing to have the same top speed on 4s as this KB. This motor has some serious torque. I would like to see how it does on 5s. I can't wait to try out the 12xl on 10s in my aftershock!

and i can't wait for some vid of those setups.

Guess I need to buy a digital camcorder!

Good lord, if I made vids of all of the cars and trucks it would take me all week! Maybe I can do a walk thru of my rc workshop! I would have to tidy it up first!

Mr. Lincpimp,

I do believe it's time! It's time to buy a camcorder for the sole purpose of sharing your awesome setups in action with your friends here on RC-Monster!

The friends that talk about their setups and the friends that talk about your setups.

The friends that show you vids of their setups in ACTION.

Now what's missing from this picture? :lol::rofl:

Good point Sike.

I still remember the first time I saw your emaxx vid from the link on your ebay auction. Thought to myself: "man this guy can't drive, but it looks like fun!"

Ok, so any suggestions on a camcorder, I am cheap, so keep that in mind. I will also want some sort of vid editor, maybe something that comes with the camera. And then where/who is best to use for vid hosting? Youtube looks like the most popular, but can photobucket do vids? Seem to remember that they can.

I will have to dress up if I am to appear in any of thse vids. And I may have to have some "female assistance", in case the truck flips over. These vids may be funny, I will have to put disclaimers on them all.

On a side note, I just acquired a golf cart, free. It needs a fair amount of work, mainly in the battery and wiring dept. It would be cool to rc that.

My driving skills have improved greatly since then! Thank you very much LOL

I figured you would have some good ideas on how to "class up" your vids.

I use a JVC Everio 30 Gig Hard drive camcorder, model GZ-MG130

It's a nice unit with alot of features. It's gonna set you back a little over $300, but you'll be glad you spent the extra dough if you decide to get it.

It comes with it's own video editing software OR better yet, you can just use windows movie maker to do your magic.

It plugs directly into the computer and you can download vids from it directly to your hard drive.

A nice feature also, you can burn vids directly to a DVD and play them later on your regular player.

Get you a tri-pod.

Photobucket will host vids, but usually tends to be alot slower at uploading than Youtube.

Most regular digital cameras now days come with video capability that ios more than good enough for You Tube quality.

You can probably get a decent digital camera and big memory card (for lots of good RC vid and pictures) for less than $200 now days.

Chek around on line at place like BUY.com or overstock.com for clearance stuff of last years models. You can find some awesome deals if you look.