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Old 08-02-2012, 04:06 PM   #136
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I've been playing around with my RS4 Pro... I've recently put it back on track with a Tekin 17.5 motor and guess [email protected]@?! I'm running the SAME exact times as with my TCX. Go figure. Here it is with a 3.5 (yes 3.5). I was running it outside (raised suspension) just to see how fast it would go with the 2 speed transmission RUNNING UNDER FULL ESC BOOST!!! Needless to say it was crazy stupid fast. If it wasn't for the 4WD, I would have had some serious traction issues when the 2 speed tranny shifts. I ended up taking it off since I just didn't have enough runway to have a good time. I did hit top speed. Given my Emaxx was GPSed at 41mph, this RS4 with or without the 2 speed was crazily much much faster... Probably well over 60 mph. I will have to calculate the speed since I don't have a light enough GPS that wouldn't affect the speed/handling of the car. The 2 speed tranny is shown in the last pic.

(I tried to attach the pics to be within the file using the IMG command but it didn't work. The file storage I'm using is SkyDrive. Does it not work with Skydrive?)
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HPI RS4 PRO brushless upgrade-wp_000184.jpg   HPI RS4 PRO brushless upgrade-wp_000186.jpg   HPI RS4 PRO brushless upgrade-wp_000185.jpg   HPI RS4 PRO brushless upgrade-wp_000187.jpg  
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Old 08-03-2012, 12:20 AM   #137
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Thats funny, I was just doing some testing on mine this week also. I have an eagle tree logger that I run first for an amp check then I tape my phone to the car and record top speed with my speedometer app. I got the best speed out of it by using my Castle 4600kv and 48p gears 84/33. Top speed was 38mph @ 68amps. I geared down a few teeth because my motor was running 152 deg and the esc was 125 deg. My Rs4 Rally cars both run castle sct escs and the 3800kv motors. one runs a 4pole and the other is the older 3800kv. They don't cog the same so I don't think they are both 4 poles. both cars run the same top speed, 31mph also around 70 amps. These setups are much cooler and I think I can get more out of them but I just haven't messed around with gearing, besides they are plenty fast on those rally block tires. I can't say I'm disappointed but I thought the speeds were higher. In all honesty anyone who sees them run is amazed and if they went any faster I don't think I'd be able to control them.
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Old 08-08-2012, 05:49 AM   #138
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Well I posted a while back about sharing some pics, almost three months ago

Finally, some pics, albeit not great pics but all I have is my phone at the moment:

Here is an electric RS4 frankenstein. Started out as a Rally, converted to on-road so it has 200mm width
MIP nitro RS4 alloy CVDs front and rear
HPI carbon graphite(molded) front/rear bulkheads and front knuckles intended for the Pro 2
HPI carbon graphite(again molded) front/rear ball diffs with ceramic balls
HPI woven graphite chassis, top deck, front/rear shock towers, and side belt tensioner
HPI urethane rear belt intended for Pro 2
HPI heatsink motor mount
Pro 4 threaded shocks
HPI clamp-style alloy hexes
HPI sway bar set
Lunsford titanium turnbuckles and hingepins
Steering bellcrank mod (turnbuckle in place of bent wire)
HPI two-speed currently with 96/90t 48pitch spurs and 19/25t pinions
Novak 3.5R GTB combo
Bluebird super speed servo
Alloy hardware (screws, ball ends etc.)






The other car here is also a frankenstein (on-road converted rally)
Lunsford titanium turnbuckles
RPM ball cups
Bellcrank mod
HPI sway bars
Robinson Racing spur gear adapter

I used this car to race with friends running Sprint 2s, other RS4s, and a Pro 4.
Using the car as shown (has JR sport servo in pic, back when racing I used a JR Z590M), with a D6 quad mag can, 9T trinity armature, and cobalt 2 enbell, and the LRP Quantum Comp 2 esc, I was often the fastest. I was the only one running brushed stuff, others had Castle 5700kv-6900kv, the guy with the 5700 equipped Pro 4 beating me out once my motor was due for a comm truing/fresh brushes. Everyone was also running 2s lipo(notice the holes on battery hold down), and geared for around 50mph top end, with this car bumping 52s when the air was right.




The RX8 was the 'racer', the M3 is the bling car (taken out once in a blue moon)







These cars handle high power very well, as in 'control-ability'. They have tons of grip with HPI x-pattern belted tires and proper setup, and are very light. I've had funky things happen due to high power though, such as shearing the spring pins that drive the plastic pulleys on the top shaft...into three pieces (on the racer), melted a graphite diff due to slip from the rear end hopping during a speed run (on the bling car, approx 65mph), and also this:

That happened on the racer while exiting a corner, no funky jumps or jolts, just pegged the throttle and the car said no... my guess: too much grip and power for an old steel component
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Umm, what does overkill mean again?

Last edited by meno1103; 08-08-2012 at 09:08 AM.
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Old 08-08-2012, 07:30 AM   #139
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Breaking a drive shaft at that point is IMPRESSIVE!!!
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Old 08-08-2012, 09:32 AM   #140
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Quote:
Originally Posted by M3Armand View Post
Breaking a drive shaft at that point is IMPRESSIVE!!!
I think maybe that particular one didn't age well

That was a front one, and I've broken a rear one as well but during a hard tumble and it snapped at the u-joint.


Impressive was one fluke save this car did once:

Again, while coming out of a turn, I was on the inside of the turn trying to cut in front of another driver (me with the RX8 body, other guy with a C6 vette body) my car traction rolled, and as it flipped sideways heading to the vette, the roof of my car met the other's, bounced off, and landed on all four with only one car length behind. Other than the moment my car was airborne, no time was lost. As soon as it landed, I got back on the throttle. Man how I miss racing these things
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Umm, what does overkill mean again?
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Old 08-18-2012, 07:43 PM   #141
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meno, nice cars thanks for sharing!

It's funny I started the thread trying to convert a pro to a rally...
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Old 08-18-2012, 07:44 PM   #142
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Anyone running a 6900kv motor? I'm topping out under 40mph and can't seem to work out the gearing.
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Old 08-25-2012, 05:20 AM   #143
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Quote:
Originally Posted by IH8VTEC View Post
meno, nice cars thanks for sharing!

It's funny I started the thread trying to convert a pro to a rally...
Thanks! Yeah, guess we went opposite directions huh?

Quote:
Originally Posted by IH8VTEC View Post
Anyone running a 6900kv motor? I'm topping out under 40mph and can't seem to work out the gearing.
Have you solved this yet?
What is your current gearing? I've ran a 5800kv and it was happy at 90t/24t for on-road with high speed/sweeping curves. I'd imagine that a 90/20 would be a good starting point while keeping an eye on temps throughout a full charge, especially if using 5000mah batts. For running on lots or street, you shouldn't have too much trouble hitting 50mph with a 6900kv motor unless you have a truck or van body on the car.
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Umm, what does overkill mean again?
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Old 08-26-2012, 03:25 AM   #144
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Quote:
Originally Posted by meno1103 View Post
Thanks! Yeah, guess we went opposite directions huh?



Have you solved this yet?
What is your current gearing? I've ran a 5800kv and it was happy at 90t/24t for on-road with high speed/sweeping curves. I'd imagine that a 90/20 would be a good starting point while keeping an eye on temps throughout a full charge, especially if using 5000mah batts. For running on lots or street, you shouldn't have too much trouble hitting 50mph with a 6900kv motor unless you have a truck or van body on the car.
I have not solved this. I have tried so many combinations that I don't know where I'm at now. Are you talking about 64p gears? I've tried both 64 and 48. I have a lot more combinations in 48 because that's what my rally cars use. the body I am running is the gtr in my avatar. I thought I might have geared too high and it's not letting the motor unwind and get up to speed. I'll see if I have the 90/20 in 64p.
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Old 08-26-2012, 05:30 AM   #145
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Quote:
Originally Posted by IH8VTEC View Post
I have not solved this. I have tried so many combinations that I don't know where I'm at now. Are you talking about 64p gears? I've tried both 64 and 48. I have a lot more combinations in 48 because that's what my rally cars use. the body I am running is the gtr in my avatar. I thought I might have geared too high and it's not letting the motor unwind and get up to speed. I'll see if I have the 90/20 in 64p.
I was referring to 48 pitch gears, lack of info on my part

Technically, in either pitch, you would get the same ratio. However, the ones that will mesh, when talking about a 90/20 combo are the 48p gears (that combo on 64p would be too small for the gears to even touch).

I took a quick look at a good tool here:
http://scriptasylum.com/rc_speed/top_speed.html
NOTE: Aerodynamics, drivetrain drag and tire 'stiction' impact top speed negatively, while in some instances wind pushing the vehicle impacts positively.

Use these numbers for HPI RS4 Sport, Pro, Pro 2, Rally, Sprint 2, and any car with the same diff tooth number and top shaft pulley tooth number (32T for diff, and 15T top shaft pulley)

* Enter Front/Rear Differential Gear Ratio (?): [enter "1"]
* Enter Transmission Gear Ratio (?): (32/15) [enter "2.1333"]
†† Enter Additional Gear Ratio (?): leave as "1"
* Enter Spur Gear tooth count (?): [try different values]
* Enter Pinion Gear tooth count (?): [same here]
* Enter total battery voltage (?): [8.4]<<fully charged lipo
4.2v Lipo max
2 cells
* Enter kv rating of brushless motor (?): in your case=[6900kv]
* Enter tire diameter in inches (?): measured a HPI wheel/tire[2.5]
†† Enter the added radius of tire
"ballooning" in inches (?):
†† Enter Current draw in amps (?):
†† Enter motor resistance in Ω (?):

This will give a good estimate on speed. I leave out the ballooning as doing so counters some of the speed loss due to drag, making the estimate closer to real world speed.
When I ran a 5800kv geared at 90/24, this tool shows that I was around 45mph (45.29).

With a 6900kv and 90/20, this calculator shows 44.9mph as the estimate. Gearing 90/24 shows 53.88, so the 50mph goal is definitely achievable .

You could go straight for the 24t, just keep a temp gauge handy and don't let that motor get over your comfort zone (I'm usually okay with anything under 170*, some opt for under 160*). Keep in mind that the longer the runtime, the higher the gear ratio should be (lower pinion/larger spur=lower top speed) to prevent heat buildup.
In other words, if you gear for some speed, don't run it hard until the whole pack drains, do a couple pulls and let it cool/check temps/drool etc.
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Umm, what does overkill mean again?
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Old 08-30-2012, 09:13 AM   #146
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I played around with the gearing going off your post and clocked 41mph with 90/21 gearing. I need more space for the motor to unwind. The downside is things heat up pretty quickly. I'm only doing this out of curiosity, I kind of want to see what an r/c car looks like going 50. For normal gearing I'll stick to the mid 30mph range.
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Old 09-12-2012, 10:41 AM   #147
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It's so sweet people haven't given up on the old PRO's. I have an old PRO 3 with the Penguin racing upgrade kit, which is a top brace. The car handles great with it. I've dusted it off and now waiting on new tires, and body to arrive. Planning on putting in a new servo, since the one in it now, is just a cheap standard one that came with my radio. Also, after reading this thread, I better go buy some new pinion and spur gears.
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Old 10-10-2012, 01:19 PM   #148
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So glad I found this post... I have 2 original RS4s. My son (who is 10) found it in the garage stored away... Going to do some upgrading! Glad to see there are people who still believe in vintage RC! Now my son and I can enjoy a new found hobby together.
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Old 12-18-2012, 07:51 AM   #149
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Hi everyone, I recently was given an RS4 Pro2 and Pro3 and I upgraded them to brushless and lipos.

What I'm wondering is, are there any parts I can buy to fix up the differentials and perhaps retrofit some kind of slipper clutch setup?

Where is the best place to get spur gears?
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Old 12-30-2012, 04:36 PM   #150
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How much is this car??
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