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Schumacher Mi4

Old 01-02-2013, 12:55 AM
  #3736  
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Originally Posted by JohnPrz
I like that idea ... I'll feel more comfortable sanding a $0.10 screw than drilling out 10 holes on a $70 chassis. I do think that some of my screws have the thicker than usual head.

Even with a brand new belt, with the front diff on the center setting, I can push the belt down a good centimeter easily, probably more (not at home now to do the measurements). I think belts can be run a lot looser than people often think and I'm probably dealing with chassis tweak more than the belt issue. It's just that my old belt (which admittedly had been in there a while) was pretty beat up, but it could have stretched too.
I wouldn't worry about the screws, unless they're causing problems with tech.

For the belts, I do usually aim to have the front tighter-feeling than the rear, because I feel the transition onto power is squirrely if the rear is too tight. You might just need new belts. Also, make sure the top teck is on and tight before you look at tension. There's a surprising amount of flex without the top deck.

-Mike
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Old 01-02-2013, 08:20 PM
  #3737  
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They are funky and itís all been done in an effort to tame the rear. So first off, itís an MI4LP, donít know if I mentioned that. Although probably moot at this point since the car is now down to the bare frame. So I also canít give you everything you asked for. Iím going to rebuild the car, checking for binding, bends and cracks everywhere and will report back. On the tear-down I realized my right rear arm wouldnít drop of its own accord Ö something was binding, so maybe that was it. Beyond that, Iíve been running:
- Yellow springs in front, white springs in back
- Shocks fully laying down in front and fully standing up in back
- Stock anti-roll bar in front, none in back
- 35 weight shock oil all around
- Spool in front, Spec-R gear diff in back
- 2 degrees negative camber all around
- No toe front or back. (will add a degree of toe in on the rear in the rebuild)
- 85 spur / 30 pinion
Back when I was allowed to run hi-flow bodies, I had been running an LTC-R, then recently switched to a Mazda Speed6, which I thought helped a lot. In the new class that requires the X-Pattern tires and more realistic bodies, Iím running an Acura NSX body, but I will move to something else as itís too low in front and I have to mangle the body to get it to fit over the shock towers. Any recommendations on a realistic body that handles well?

Also, not sanding down the screws for any other reason than to be able to lay the chassis flat on a piece of glass to check for binding.
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Old 01-02-2013, 08:59 PM
  #3738  
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Originally Posted by JohnPrz
They are funky and it’s all been done in an effort to tame the rear. So first off, it’s an MI4LP, don’t know if I mentioned that. Although probably moot at this point since the car is now down to the bare frame. So I also can’t give you everything you asked for. I’m going to rebuild the car, checking for binding, bends and cracks everywhere and will report back. On the tear-down I realized my right rear arm wouldn’t drop of its own accord … something was binding, so maybe that was it. Beyond that, I’ve been running:
- Yellow springs in front, white springs in back
- Shocks fully laying down in front and fully standing up in back
- Stock anti-roll bar in front, none in back
- 35 weight shock oil all around
- Spool in front, Spec-R gear diff in back
- 2 degrees negative camber all around
- No toe front or back. (will add a degree of toe in on the rear in the rebuild)
- 85 spur / 30 pinion
Back when I was allowed to run hi-flow bodies, I had been running an LTC-R, then recently switched to a Mazda Speed6, which I thought helped a lot. In the new class that requires the X-Pattern tires and more realistic bodies, I’m running an Acura NSX body, but I will move to something else as it’s too low in front and I have to mangle the body to get it to fit over the shock towers. Any recommendations on a realistic body that handles well?

Also, not sanding down the screws for any other reason than to be able to lay the chassis flat on a piece of glass to check for binding.
I think you've gone way off the reservation trying to calm the rear and made the problem worse.

For setup, I would start with the kit carpet setup, and then make the following changes:
+ Springs: Blue front, white rear. If you have HPI Pro 4 springs, start with Pink front, Silver rear. That may be a touch on the soft side.
+ Ride Height: 5mm front and rear
+ Toe: zero or just .5* out in front, 3* in rear (which should be kit, as there's toe-in built into the rear suspension blocks)
+ Camber: -1* all around. The X-Patterns don't seem to like a lot of camber. EDIT: I think this is partly due to the tire itself, but also partly due to the taller tire with lower ride height putting the stock geometry into a more aggressive part of its camber curve.
+ Droop: 1.5-2mm up travel in front, 2-3mm uptravel in the rear. That will be something in range of 6mm on a gauge, maybe 7mm, measured under the arm at the outer hinge pin. Measure the front under the front of the arm, as it's thicker than the back of the arm. I usually adjust to the same gauge value both front and rear, but .5mm higher number in the rear is probably better. Too much droop will make the car wallowy and harder to drive, and possibly traction-roll prone.
+ Shocks: 45wt AE or equivalent. 100% rebound. I've been running drilled caps recently, but I think undrilled might actually work better, since the extra rebound will help support the car with the softer kit springs and help give more response. I like thick shock oil, so depending on your tastes, you might have to go down.
+ Shock Positions: 1-hole up in front, all the way down in the rear.

I'd be surprised if that doesn't get you in the ballpark.

As for bodies... I've had good luck in the past with the 190mm HPI R34 Skyline GTR4 #7327. It's low and very light. It doesn't have any easily-cracked features on the front end. One of the guys I run against is using the Mercedes Benz CLK DTM #7357, and doing very well. I run the Subaru Impreza 7399, and it's heavy and can cause traction roll when driven hard, so I would steer clear of that. Any of the HPI 190mm Sedan-type bodies that are low and have a small TC-style wing (as opposed to the big heavy one like the Impreza has), are probably safe bets.

If you've got a droop gauge with blocks, just put the blocks on the flat setup surface across the chassis under the droop screws. That will make sure they don't hit any screw heads, and if the chassis doesn't rock on the blocks, it's not tweaked.

Are you running boosted 17.5? That gear ratio sounds awfully high for blinky. The X-Patterns are taller than typical TC tires, but not that much taller. If you're running blinky, I'd drop down to about 4.2 and go from there. A 5.1 could be giving you way too much rip. If you do that, consider dropping down to a 74T spur. That will move the motor back, putting more weight on the rear, which might help to calm it down.

Make sure your hinge pins are still straight while you've got it apart. If you're using the screws in the hinge pins, you'll have to sand the kwik-klips quite a bit to keep the arms from binding.

Also, make sure your tires are well-glued. If you're running chrome rims, don't do that again on your next set.

EDIT: Also, turn the dual-rate down on your transmitter. If 85% doesn't get the car turned, your setup is too pushy.

EDIT2: Also, the X-Patterns are touchy with sauce. 1/2 to 2/3 front sauce is good, depending on grip level. With Jack the Gripper, I keep them wet for a long time. With SXT3.0, which seems more aggressive, I give 'em about 15 minutes. I haven't tried sticky fingers (I have some, just haven't gotten around to trying it), but since it's allowed at our track, it must be somewhat similar. I clean thoroughly with motor spray after each run.

-Mike
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Old 01-02-2013, 09:22 PM
  #3739  
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Thanks Mike; lots of good advice and I think you're absolutely right about putting the car back to stock carpet. I'll check out those bodies, maybe also the HPI BMW M3 GT body #7352, which seems to fit your criteria.

Will definitely check all of the hinge pins. I've got the ultrasonic parts cleaner and will cleaner everything up before reassembling. While I've got it apart, right?

And I'll also try your way of checking for tweak ... much easier than filing all of the screws down.

Just a few more questions:

I'm running white wheels ... and my LHS only had +3 offset, essentially making the car 196mm wide, so I have to make extra large wheel wells, but I can get past that. I can also always go to a 200mm body, but from a handling perspective, any thoughts on wheel offset? Should I try to find 0 offset, and if so, do you have any that you recommend? I'm having a hard time finding wheels that list their offset. I prefer white wheels for the visibility.

I also have a big heavy wing on my body, because the original wing cracked off and I couldn't reattach it, and well, this is allowed me to run the body I brought. I didn't even think about the implications of the extra weight ... I was just going for downforce. So I should definitely order up a new body.

I was surprised that you suggested moving weight back to calm the rear of the car. I run high performance DE events in 1:1 cars (another hobby) and Porsche 911s (especially the older ones with less sophisticated suspensions) can be very tricky to drive specifically because of all of the weight in the back, which can induce oversteer very easily. The example that is always given is that if you slide a hammer across some ice, the head of the hammer (the heaviest part) will usually wind up leading the way. Mid-engined cars with more weight in the middle tend to be very neutral but can wind up spinning like tops and front engined cars are usually more biased to understeer (forgetting everything a manufacturer can do to tune this out). Again, this is in the 1:1 world, so maybe things are a little different here.

I really appreciate your time and thoughts.

John
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Old 01-02-2013, 11:02 PM
  #3740  
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Wheels: Try looking here for part number reference:
http://www.hpiracing.com/hpiwheels/touring/

I personally like the Split 6 #3795 (it doesn't list an offset, but I don't see any non-zero offset part numbrs), because they look cool and seem pretty sturdy. I have also used the TE37 (#3835 for white +0 offset) which also look awesome in white. They also have #3695 Super Stars, but HPI Europe says they're 1mm offset.

Anyway, I don't have any experience with non-zero-offset rims. Even the Vintage fronts are 0 offset. You could try the narrower hexes, but everyone runs those in front already anyway. You could try less shims behind the hinge pin blocks, but that affects a lot of things, like camber link length and shock positions, and you need to be careful about the CVD bottoming out and binding.

Or, you could just not worry about it, and run a 200mm body. I've seen locals do well with the Pagani Zonda, Ford GT, and Mercedes Benz CLK GTR. I think they may have all been running the Vintage rims / tires, though. Someone in the USGT thread had success with the Toyota MR-S GT. I have one of those, but haven't gotten around to trying it. The 200mm shells tend to be heavier, though, but you can run a wider track width with them.

As far as moving the motor, it's a tuning option. When I ran VTA on asphalt, my car was super loose entering corners, and going to a larger spur/pinion helped tame that. I've tried moving the battery to the forward position in 17.5 TC a couple times, and it's interesting. It was pushy on entry, but rotated a bit more under power and the back end felt livelier. So it kind of depends on your other electronics and how the car is working.

-Mike
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Old 01-02-2013, 11:24 PM
  #3741  
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Just thought of something else. I've been running the diffs in the high position with the X-Patterns, to keep the axles straighter. It's not something I've thoroughly tested in isolation, but I seem to think it makes the car more predictable.

Of all the stuff I mentioned, though, I'd say the droop is probably the single most important. Droop will be different (on the gauge) compared to TC tires, becaue the X-Patterns are taller, and if there's too much (particularly in front), the car will just drive like poo on carpet. It'll roll alot and the front end will dig in and be really unpredictable.

-Mike
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Old 01-03-2013, 05:26 AM
  #3742  
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Awesome; hadn't thought of adjusting the diff position for the taller tires; will try that as well. I like the TE37 wheel in white, so I'll order that up in 0 offset. Which foams are you using? I'm looking at the HPI pro-molded green. Since I've only run one place, I'm not sure how to classify it. Although it's carpet, it's not a virgin rug so to speak, and is often a bit dirty.

Now just waiting on some parts ... ordered new new spool outputs, ball bearings all around and new titanium hinge pins. A new front belt is going on, back one looked fine. One of the front arms had a hairline crack ... nothing that would affect handling though. I think the real issue might have been a bit of binding. Will make sure there is free movement everywhere (and also check out that front belt on reassembly!)
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Old 01-03-2013, 10:53 AM
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I use the inserts that come with the tires, because that's what our rules mandate.

-Mike
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Old 01-03-2013, 12:02 PM
  #3744  
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Just thought I'd chime in on the body subject, The HPI Mercedes is a great body, as it's light and has a decent wing. I would recommend the HPI Porsche 911 Turbo over the Merc. The wing is better, and is 2g lighter even with paint. Great handling as well.

Everything else Mike has pointed out is spot on, especially with the x-patterns. I do feel these are a faster option for me over the vintage tires, but they do require some extra care because of how they wear/grip on carpet.
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Old 01-15-2013, 01:25 AM
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I am getting the SpecR gear diff because I dont want to clean ball diff all the time. I want to know if there is any building tips to make them durable. every one in my local track who run mi4 with gear diff has stripped many time including one very experience racer. please let me know what should I be looking into while building the diff
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Old 01-15-2013, 04:36 AM
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Originally Posted by Car Breaker
I am getting the SpecR gear diff because I dont want to clean ball diff all the time. I want to know if there is any building tips to make them durable. every one in my local track who run mi4 with gear diff has stripped many time including one very experience racer. please let me know what should I be looking into while building the diff
If you race modified or run on a grippy track don't bother
They are no good, found out from my own experience
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Old 01-15-2013, 07:00 AM
  #3747  
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Originally Posted by Car Breaker
I am getting the SpecR gear diff because I dont want to clean ball diff all the time. I want to know if there is any building tips to make them durable. every one in my local track who run mi4 with gear diff has stripped many time including one very experience racer. please let me know what should I be looking into while building the diff
I run mod on a very tight carpet track, I like the feel and consistency of the gear diffs.

I have run into the same issues, but have been starting to get them to work properly.

All the SpecR diffs are the same, only thing that ever differs are the outdrives and housing. Have a look around and read up on them.

Make sure you shim them, not too tight, but enough to make sure the gears mesh comfortably. I was always stripping the deep end, never the top.

Choose the right oil for what you are running. I go by faster you go, faster the corners, and more stress on the diffs, the ticker the oil.

When driving the car, make sure you are not lifting and spinning up wheels on corners, when the wheel hits the ground again the stress goes straight back through the diff. If you have an off or get stuck somewhere, get off the power don't try and force your way out of it, wait for a marshal. i have stripped a few diffs doing that.
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Old 01-15-2013, 12:12 PM
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They are absolutely fine if you shim them properly - note, properly, not as the instructions tell you!!

The most important thing is that there is no play in the output shafts - to get this, you need at least 2 x 0.1mm thick shims between the output cups and the casings on each side. I often have 3 shims on one side. You usually get 2 off these shims in the pack (the smaller diameter ones) so you will need to get some more.

In all the time we have had the diffs, I have probably broken 2 gears max - running mod etc.
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Old 01-15-2013, 12:47 PM
  #3749  
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been following this thread for months. finally ordered one. gonna start off on the x-patterns as you guys have recommended. any insight on largest mah lipo to run ont his? looking at road racing it and want longest possible time avaialble.
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Old 01-15-2013, 01:44 PM
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Johnprz: I was having the hardest time taming the rear for my Mi4 ever since it came out. Car was great...except the rear would occasionally jump out mid to corner exit. While I didn't read everything you posted on your problem, I quickly saw that you were running the same thing that I was that, once I changed, corrected everything.

DO NOT RUN WHITE SPRINGS!!! Especially in the rear! What happens is the chassis can hit the track causing the rear end to loose traction.

In Europe they don't run on the pristine, high traction tracks we have in the US so a soft setup is needed (I actually still have a setup sheet for the Axis or one of the other vintage cars that described the track conditions as 'wet, leaf covered track'). Once I gave up on trying to soften up the rear (the old cars we ran STIFF springs all the way around... like 65-100lb springs) and just increased the spring rate all around, the car came ALIVE! Run the setup that Gripgoat posted as a starting point and if you still need help, ask again, but I feel VERY confident your problem is the white springs.
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