New hi-speed project
 

I've done a few off-road conversions and now want something that I can hit really high speeds with (100mph+). I looked at a few electric sedan kits, but want something that is built more on a 1/8 b/truggy platform.

From what I can tell, the Ofna Ultra GTP would fit the bill. Plenty of chassis space, 2 speed, solid design etc. I was thinking of getting just the roller for now, but am thinking that getting the RTR and selling the parts I don't need (radio, engine, misc parts) might be the better way to go because it will have the body, steering/brake servos, and the 2 spd already installed. The RTR is listed as $320 and the roller is $190 at nitrohouse. I'll check a few other places first of course...

Then, to get the high speeds I'm looking for; use the two speed "tranny", 6s lipo, and a Neu 1512 motor set to run around 45,000 rpm. Since I'll be using the 2 speed, I think I'll need the Tekno clutch adaptor and just set the shoe spring very loose so it grabs right away.

Even though this vehicle looks to be the winner, I'm open to other ideas. One reason I like the Ofna one is the easy LHS supply.

This project would get started a lot easier/faster if I could get a few hits on this first (hint hint). :yes: :wink:

EDIT: Added info (more for me for future reference):

Tire diameter: 4.25"
F/R diff ratio: 3.1428 (44/14)
Stock 2 speed spurs (2nd,1st): 45T, 49T
Stock 2 speed CB (2nd,1st): 18T, 14T
Optional 2 speed spurs (2nd,1st): 44T, 47T
Optional 2 speed CB (2nd,1st): 21T, 17T

Ugg. To get a theoretical 110mph, I'm gonna need to get the optional spur/CB set, and get a 1512/2d (kv=2600) and spin that sucker at almost 58,000 rpm.

Good to hear that you are going for high speeds now BG. It's hard going fast in a straight line, and gets your heart pumping pretty good. What tires are you planning to use?

Welcome to the club :lol:. I'm glad I'm not alone in the chase for High Speed.

Don't know about much other than the vehicle itself. From what I've heard, a good set of foams may be the best thing to use, right? Then, mounting them so they are perfectly balanced is imperative at the speeds I'm going to try to hit.

If I can't get a 2spd spur/pinion combo right to reach those high speeds, I might have to go with a single speed and use a very large pinion. But then, I'll need a larger motor (1515 or even the 1521) to generate the low-end torque since it will be geared so high.

I think I'm going to try to make the battery tray and the ESC/Rx mount out of fiberglass to keep the weight down. Should be interesting...

The 1521 would be a nice choice. I will use the 1521/1.5Y to make my speed machine.

:gasp:A 1521 spinning at that kind of rpm would draw LOT of current. Plan for some serious battery packs and asc if you want to pull 60K rpm with a 1521!!

That RPM was based on using the max size spur/CB setup available for the 2 speed setup. I was kinda leary about those high rpms as well. If I went with a single speed setup, I wouldn't be as limited by what 2 speed gears are available and use a larger pinion and/or smaller spur. That would bring the required rpms down a bit. Heck, I could even try a direct drive setup using an outrunner, but would have no gearing options and would need to control top speed via voltage and motor choice only.

I used my 1521/1Y with 37V and that was some awesome power. Too bad the drive train didn't hold up. The six gears inside the rear diff had a little melt down. I will eventually get this http://www.vertigoperformance.com/products_Lockers.html to save my diffs.

I would not get the lockers. The will make it almost impossible to even get to high speeds. I had on in my Maxx and I couldn't hardly get about 50 with it.

i'm planning on going hv with my yosa rally project. i'll tell you my plans and maybe itll give you ideas or maybe you'll tell me im shooting myself in the foot.

pistix
12s air esc
12s a123
kb45xl motor 1000 or 1200 kv
2speed setup
what ever tires will hold up

i would realistically like to break 80mph with the setup, but idk if it'll do it or not. i haven't played much with the speed cal. so right now i'm clueless really. i have a kb in my very heavy emaxx running 6s2p a123 and i'm very impressed with that motor. i figured i would stick with it for this project because of price and the fact its got so much grunt.

Before I installed the buggy diffs in the truck, the rear truck diff had locked and it was actually working better then before.

Sounds interesting.

You might want to play with the calc cause you'll find that you need quite tall gears, larger tires, higher voltage, higher kv motor, etc to reach those speeds.

Tires are gonna be tough. I don't think anything short of using foams or solid rubber will work since it will be really high to prevent ballooning.

Hey Brian, check this out: http://www.rc-monster.com/forum/showthread.php?t=9179

The car is very similar to the GTP in design. Plus it has a two speed! I am only trying to get to 70mph, but I can gear up if needed. You should have fun with it, my 10th scale tamiya that can do 80 is a blast, body choices will be critical, downforce and airflow management will be a big concern.

Actually, I was looking at that project a while ago. I liked the way it was built, but not sure how easy parts availability will be at my LHS. Of course, I could get them directly, but sometimes it's just easier to call up the LHS and tell them to get it for me.

I understand about parts. I have bashed the snot out of my ofna mbx buggy (identical mostly to the gtp) and it has never broken, only the front bumper cracked. I only bought the Yusa cause it was under 100 bucks shipped. I doubt that i will break anything, these vehicles are so solid being based off 1/8 scale buggies, almost indestructible! And the wear items will interchange, such as diffs, etc.

Are you going to use a clutch, or one of mike's lst 2 pinion adapters?

Not sure about what I want to do about the clutch yet. I'll know more when it sits in front of me. Due to the wallet-draining holidays, I'm planning to make some purchases around tax-time (maybe a tad sooner), unless I can off-load the Hellfire roller. The under $100 price tag of the Yusa model is attractive, but I always seem to break the things that can only be found by ordering specific parts. :cry:

This is going to be good! I'd say 1521 is a good choice, and I wouldn't spin it slower than 50k RPM! Aim for 60k at nominal voltage as I think at full tap your pack will probably drop below 3.7V/cell anyway.

A car like this is probably going to need about 4 kW of power.

Brian,

This should really be a cool project! I can't wait to see what you come up with as an end product. I have been eyeballing the Ultra GTP for a long time and have been considering a similar build....except I wouldn't be going for the extreme high speeds that you are. What motor mount would you use-the CR buggy?

Not sure about the mount. Probably have Mike do something special to be strong and as light-weight as possible. For batteries, some type of cell with a REALLY good C rating, like FP or something like that. Don't need high capacity per se, mostly very high short-duration power that is as light as possible. If I can find some decent prices on 1/8" thick CF sheets, I might re-fab some of the existing Al pieces for weight. I want strong, yet durable. But it has to be pretty too. :smile:

I'm open to any suggestions if anyone can think of any...

Brian,

If you are worried about the motor mount it might be easier than you think. The DM1 I did uses the same center diff uprights as the Jammin Buggy so the RCM Jammin Buggy motor mount was a direct drop in fit. My suspicion is that the GTP is probably the same upright because it uses the same 2 speed as the DM1 so it only stands to logic they would use the same upright.

Its possible I'm wrong, I haven't checked any part numbers or anything for the gtp, but I think you have a great shot at it being a simple solution. Do some part number research on the ofna website.

And if you are looking for a simple 2 speed solution check out Mikes 2 speed pinion adapter. He now has a whole range of pinion gears available for it. I got a setup from him and it is solid and really simple setup. It should work for your application perfectly. I was also thinking about playing around and seeing if Mike could make me some "special" pinion gears for the 2 speed adapter of his. I was thinking I wanted to get a 32/37 pinion setup to use with the Ofna 44/49 2 speed spur gears on the 2 speed tranny. I was going to target 100+ as a goof around setup on the DM1 just to see if I could do it.

I'm sure he could make (or get made) any tooth count we need. It might cost a few $ to get it, but If we both want a set we could split the setup costs associated with any special gears.

I think you are right...if I were to build an Ultra GTP, I'd try the Jammin CR mount and ditch the 2-speed for a center diff....I guess for the high speed stuff this is not optimal, but it is simpler and would be fun to build/drive.

I would not spin a 1521 anywhere near 50k in a car or truck, I believe it would pull too many amps. I would spin a 1512 that fast on a good controler, consider the fan option on the neu to keep the temps well in control if you are going to spin it 50-60K

If you guys decide to have any special size gears made for the 2 speed adapter let me know. I have quite a few 2 speed vehicles ready to convert.

Also, any ideas how I would get in touch with mike? I would like to buy a 2 speed adapter from him, but need it to have a 6mm bore to fit my kb45 motor. I would drill it out myself, but do not want it to wobble. I am sure that mike's equipment is better than mine!

The gears I'm talking about wouldnt be for everyday use. WAY to tall of a gearing setup. He has the adapter and gears ready to go for most "normal" 2 speed conversion applications. I think you might have a problem with the 6mm hole though... There isnt a whole lot of room inside there to make the hole bigger. It migh be possible though. You can reach mike at rcmonstermike@gmail.com

I have tried that email address twice now, I will give him a few more days!

There should be enough material to enlarger the hole to 6mm. The stock losi clutch bell uses a 5x10mm bearing, and still allows for the thread on gears.

And I would not use them for everyday use. I am building a on road car, for straightline speed, if it all goes well. I will test it with a more sane setup first and then increase the speed to test the aerodymanic requirements. I have already done this with a 10th scale car, so I have some ideas what will work!

I hate to bust your bubble, less you want to take a push broom out and sweep 250 yards of road, a high speed sedan is not going to be too much fun, I tried it with tc3 and 1930/5

Actully I found a decent blacktop area and unprepared it allowed my tt01 based car to do 74 mph. It would have gone faster, but I need a longer space. It is maybe 300 feet long. We actually added about 20 feet to the radar position and gained about 8 mph, so I would love to have about 250 yards. I have a feeling that the car as is would top 80mph, stock out of the box with bl power and foam tires! Plus 10 guys with brooms would make short work of sweeping!

well don't take me litteral on 250 yard, but you would need 10 guys and 10 push brooms to make short of an area needed and phat chance scaring up enough people to do that, I have a hard time just finding a turn marshal or camera man

BG... that Yusa car is cheap enough you could buy a second car for parts... or even a third lol

If a rc car could close in on 100mph, I would easily be able to have 10 guys there to sweep and watch. There is generally at least 6 of when we go out and play.

I ran the 1521/1Y with 10S 4600mAh TP and the Schulze 40.160 and it did not pull that many AMPs. The 1521/1Y was spinning at around 55000rpm. The only problem was the drive train. I drew a crowd of people at the parking lot looking at the truck fly from one side to the other. I still have to try my 1527/1.5Y, but I'm waiting for my custom 58.8V packs and I might have to trim one of the braces from the truck to make the 1527 fit.

About the amp draw: I won't be spinning the motor at ~55krpm all the time - just when I'm trying to hit really high speeds. For normal play, I'll be gearing down and/or using less voltage and/or using the EPA to limit motor speed.

Still not sure about whether to use two speed or not. But, I can decide that on-the-fly since the single speed/2 speed setups are interchangeable. I just have to remember to use mechanical brakes for the 2 speed. 2 speed would be easier on the motor since it won't have to pull such a tall gear on take-off, but the 1515 or 1521 are pretty powerful motors. My 1512/2d on 4s has no problems pushing my overgeared buggy to around 55mph, and I'm going to try to make this vehicle as light as possible.

For the motor mount, I will probably see what Mike has already and go from there - or make my own. Balance will be very important for something like this, so I have to really do my homework on device placement. The plan is to do a typical setup where the motor is on the steering servo side, battery on the other, ESC/Rx wherever it will fit. I'll probably leave the brake servo where it is, just pushed out to the side to allow room for the motor there.

Yeah, the yusa models are cheap, but I tend to break the same part so I don't want to have 5 chassis's laying around. :smile: How long have they been around? I don't want to buy myself into obsolescence.

I just did a little part number research for the center dif uprights on the GTP. They are different than the Jammin center dif mounts so I dont know if the Jammin buggy motor mount will work. If you can give me center to center measurements on the center dif screw holes I can check it against the Jammin buggy motor moount I have in my DM1.

JHautz,

I did the same checking and cam up witht he same thing. I am hoping the OFNA online help comes on soon. I am going to see if the diff units are interchangible. If that is the case then the CRT mount will work.

Just checked with Ofna and the diff unit in there is the only one for that car. Hopfully Mike can come through with a mount for this one.

I'm not too worried about that because I can make my own mount if need be - something like what I did for the CRT.5, except use thicker aluminum. Can't forget to make the mount capable of retaining the mechanical brakes...

hey BG, how about you use lutach's 200a controller when it comes out or maybe a CC HV110, and a neu 1527 1d (2160kv), and 12s 25c lipos (polyquest)?
esc: $270
motor: $433
batteries: $776

how does $1476 for a setup sound?
:party::party::lol::lol::party:

Why not something like a 2230 on 10S using the HV85 or HV110. The 2230 might be better for RPMs since its got the are diameter rotor for the torque needed, but also a shorter rotor which would be better for high RPMs. Basically, less rotating mass.

I agree that HV is the way to go. I am going to order a great planes 60amp hv esc and the programming card. I will try it on my tmaxx first, 10s lipo on a 20xl feigao should be ok, do not think it will overdraw the esc.

Brian, the use of smaller batteries and more cells would probably be cheaper. I have seen 15-20c 2100mah cells go for $10-$15 per cell. And I am sure that a 12s2p setup of those cells would be able to get you about 4hp. Run that thru a decent hv esc, castle, knotronic, etc.

I am actually reconsidering a hv setup for my yusa car. I will test it on 4s with the 2600kv motor, but may sub in a 1300kv and run it on 10s lipo?!?

I agree on parts availability, usually there are one or two parts that break fequently, so you would end up with quite a few rollers!

I would like to go HV, but was thinking the dimensions of a many-celled pack would be physically prohibitive because of the thickness. I'll have one whole side of the chassis for the length, but think I will be width and height limited. Nevertheless, I won't be purchasing any of the electronics or batteries until I get the vehicle in my hands, the motor mount made, and the rest of the layout sketched in.

I'm really anxious to start this now. Might have to check my bank account to see if I can shift funds around a bit. :smile: