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About nbTMM

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  1. The problem is that with RCs we have a warped perception of speed. It is easy to make a 1:10 RC drive like that truck by putting super soft springs in it and driving at 10-15kmh (100-150kmh scale speed) but most would be unimpressed with their RC not being able to do over 15-20kmh without bottoming the suspension. When you put hard springs/shocks in it so it doesn't bottom out at 50kmh+, it stops looking 'scale' from any vantage point as everything is happening lightning fast. If you drive it at 50km/h with hard springs and take a slow motion video, it does however look more realistic. The Traxxas UDR is probably the best compromise I've seen. It's reasonably big and has soft and massive suspension travel, so it can go quite fast while still looking reasonably scale. In slow motion it looks 100% scale.
  2. The heavier the car and the higher the center of gravity, the more weight will be transferred from the inside to the outside wheels in turns. More weight on the outside wheels does generate more grip, but not enough to compensate for the grip lost on the inside wheels. Also, if too much weight is transferred to the outside wheels the car can have a tendency to roll over (traction roll). Therefore you want to minimise weight or move it as close to the ground as possible to increase cornering grip and handling. A lighter shell, mounting the shell lower on the body posts and lowering the suspension of the car achieves this. If the body or chassis are too low and bottom out on the road, it could however unsettle the car.
  3. As above, first check that forward is actually forward by changing the running mode in the ESC settings to forward/brake only. On most sensored systems, the direction that the motor rotates is non-negotiable as the motors run advanced timing and make more power/rpm in what is considered the forward direction. The 10BL120 is no exception - there is no setting to make a sensored motor rotate backwards, so forwards is permanently mapped to one direction and brake/reverse to the other. You can't swap the motor wires on a sensored system like you can with a sensorless - doing that will make it run poorly if at all because the windings won't be timed correctly with the sensors. If you swap the direction of the throttle channel on the transmitter, then the ESC thinks you're reversing when moving forwards and may impose a limit on the amount of throttle and you'd only get brakes when reversing (when the ESC thinks the car is going forwards). You can program the ESC to run forward/reverse only (no brake) and set the reversing speed to 100%, but then the motor would also be running with retarded timing when going forwards, and advanced timing when reversing so it would go faster in reverse and run hot/inefficiently when going forwards. The compromise then is to set the timing on the endbell to 0degrees (and disable any turbo/boost timing in the ESC) so the motor makes as much power in both directions. Be aware that the minimum mark on the endbell may not correspond to 0degrees, but instead be 10-20degrees on some motors. Some motors may also physically prevent you adjusting the timing all the way down to 0deg. Also, many shaft driven Tamiya chassis you can install the diff(s) backwards, which will change the direction that the motor needs to rotate. Maybe you've installed your diffs backwards?
  4. Some people drill a small hole in the shock cap which vents pressure from the air pocket inside, therefore the diaphragm acts like a very soft spring until it is deformed hard against the shock cap or stretched to it's limit into the cylinder. Seems to be more popular to do this amongst off road RC racing. I don't recommend this, it puts undue stress on the diaphragm and will add 'slop' to the shock action as the diaphragm has to deform all the way from inverted to non-inverted before you actually start pumping oil past the piston and getting a damping action. Effectively your suspension will have a significant amount of undamped travel. If you pierce the diaphragm, oil will leak past it into the cap area and air will be sucked into the cylinder. Effectively you now have an aeration shock. How it performs depends on how much air and oil volume is contained in the shock when it is built. If your cap does not have a secondary seal, the shock will leak if you do this. Not recommended. If you want an aeration shock fill the diaphragm/cap area with blutack and leave some air in the cylinder. Same effect but won't leak. If you want the most responsive damping action you should build it like tamiya instructs. This makes the air spring as stiff as possible so more oil is pumped through the piston for a small displacement of the shaft as the air spring won't be compressing as much. This results in more immediate damping. The side effect is just that you get an air spring which acts in addition to the coil spring. This doesn't need to be an issue, just install a softer coil spring than you would otherwise. If oil leaks from the shock (which is inevitable), it will revert to having less preload - as if it were built with shaft pushed in. So if you want it to remain like how Tamiya instructs, you need to periodically open the shock and top up the oil.
  5. That TT02B is geared up as well. With stock gearing and a 5.5t it would only do about 50km/h. Coincidentally i have a 5.5t in my TT02B at the moment, but it's geared for about 65-70km/h top speed. Any more than that and it runs too hot.
  6. Hard to go past these ESC/motor combos for value and quality https://www.hobbywingdirect.com/collections/combo-special/products/xr10-justock-esc-g2-1-combo?variant=14796877398131 I use Trackstar sensored 540/3650 size motors and have been happy with them as a cheaper alternative to hobbywing. I have a couple of the Trackstar GenII 120A escs which are a rebranded SkyRC Toro TS120A, which I also have one of. The hardware is good, although the software/programming box isn't very polished. Once in a blue moon I'll have one start acting strange and it'll be resolved by resetting to default settings with the program box. For batteries and chargers, I've had good experience with anything Turnigy. Virtually any 2S hard case LiPo will fit the TT02, although I think you'll need a 'round' LiPo pack to fit the Manta ray. For charging I use a Turnigy Accucell 6 with a 12V, 5A laptop brick style powersupply that I purchased from a local electronics supplier. I see that they (Hobbyking/Turnigy) now offer chargers that run directly from mains as well which are based around the same charging hardware.
  7. Yep, just got to find a suitable road near me after I finish off the final details. Front posts are just regular front posts with the bottom cut off, a 2.5mm hole drilled and then attached through the spare 3mm holes in the standard bumper mount. Front bumper is just the standard tt02 foam one. Not sure if i'll keep it there but it seems to support the body well, going to make a FRP front diffuser which sets at the same level as the side trays. I need to fibreglass reinforce the shell mostly around the rear body posts and front wheel arches as it is too flexible for my liking. 60 spur / 42 pinion will have your peak power at ~125kmh 49 spur / 46 pinion will have your peak power at ~167kmh You can work this out by finding the unloaded max motor rpm: 6900kv * 11volts (a 3S pack under significant load) = 75900rpm Peak motor power will occur at 50% of maximum rpm = 37950rpm Then you can work out your final drive ratio FDR = spur/pinion * 2.6 so FDR = 60/42*2.6 = 3.71 or FDR = 49/46*2.6 = 2.77 Then you can work out the wheel rpms at peak power Wheel rpm (60/42t) = 37950/3.71 = 10229rpm Wheel rpm (49/46t) = 37950/2.77 = 13700rpm and finally convert that to road speeds, assuming 65mm wheel diameter speed (60/42t) = 10229*0.065*3.1415*60/1000 = 125.32kmh speed (49/46t) = 13700*0.065*3.1415*60/1000 = 167.85kmh Now that assumes that your battery and ESC can provide enough juice to actually make peak power. If your battery voltage sags, or the ESC drops a lot of voltage, you may find that you go slower when you gear for peak power. Instead you might gear for 75% max rpm at the motor where you get a bit less power (coincidentally about 75% of the max power) but the motor operates much more efficiently and is less demanding on the ESC and battery. That may make the 60/42t gearing reach a higher top speed even if you're aiming for ~160kmh Hope that helps!
  8. I have owned both JX PDI-4409MG and Trackstar TS-D99X. Not even remotely the same. 4409MG doesn't meet it's specs. It is slow as a wet week and has a big deadband (8-10us not 2us as claimed). It is however reasonably strong. All the JX servos are much slower than their spec from what I have seen. If you want an OK servo for cheap I guess they are alright. The build quality seems to be there, the performance specs are just blantently made up. 8-10us deadband starts becoming unacceptable for racing or on road speedruns. When you steer left and back to center, the car is still steering noticably left, and when steering right and then back to center, it's still steering slightly right. The smaller the dead band, the better it recenters. D99X meets its specs - fast and with negligible deadband (<3us), small enough in fact that it occasionally 'hunts' (buzzing sound as it rapidly alternates back and forth between two increments). Mine did develop a problem with a bad solder joint or some such. When the rear cover was squeezed the servo would rotate all the way to one side. In trying to troubleshoot it with the covers loose I managed to snap the plastic end stop off the front cover. Couldn't work out what the problem was, ended up binning it. I'd happily buy another at the price I paid (AUD$28), but would think twice at their current pricing ($40). The only servo I have that performed as well as that one is a Savox 1252MG but that set me back $80.
  9. The problem with pushing things too far, such as making a fully enclosed flat bottom car that is incredibly low to the ground is that while it may make significant downforce, it may also be aerodynamically unstable vs ride height. I.e. it may change from generating significant downforce to significant lift if the chassis hits a bump and pitches the front up a few mm. We don't actually need significant downforce as RC tyres generate adequate traction with just the weight of the car. What we are aiming for is an aero package which does not create lift. Running an insanely low ride height may also make the car susceptible to rubbing the ground or the wheels rubbing the body which will unsettle it. Keep in mind that the road is effectively incredibly bumpy compared to a 1:1 car and we are trying to drive at 1600kmh+ scale speeds.
  10. I use the same type of paint to back as I do to colour. E.g. Tamiya PS-1 White, then PS-5 Black. When backing white paint, there is the risk that you haven't laid down the white paint heavy enough, then the darker backing colour will show through from the outside. For that reason, if the inside of the shell can't be easily seen (e.g. it has solid or heavily tinted windows) then it is safer not to do a backing layer.
  11. If it has cured partially and is just softer than usual, you may be able to heat it up to speed up the reaction and get it to harden. Putting it out in the sun for a day or two should do it. If it hasn't cured at all the best way is to scrape it all off, sand back until you have only fully cured resin on the workpiece, and start with a fresh batch of resin.
  12. Does it have to be steel though? The only aluminium pinions I've had trouble with are the Tamiya ones made from cheese. All other brands, even cheap chinese ones from ebay, show zero wear unless sand gets into the gearbox - at that point the plastic spur is a throwaway job regardless of which pinion material you are running. If you're pressed for time I'd just go down to your LHS and give whatever they've got a shot.
  13. Just need a front splitter/undertray and a motor fan and I'm ready to get in on the action 2S, LRP 3.0t 11600kv motor to start. 'Legal' gearing as well (gear cover unmodified). Will try it on 90t spur/41t pinion first which I suspect is super conservative - peak power around 100-110kmh but should still have enough power to wind out past that. I have gone 100kmh on a 7.5t trackstar motor on 2S which is only 410Watts, lancia delta shell too lol (aerodynamics of a brick). This motor is 800Watts on 2S, so I don't see why it can't be good for just shy of 150km/h with the correct gearing. Twice the power, 1.5x the top speed - square law.
  14. 6S on a 6900kv 3650 motor is asking for trouble. I'd guesstimate that motor is about 600W on 2S. On 6S it is 5400W because 3 times the voltage is 9 times the power. The motor will burn up very quickly. 1000W on a 3650 is about the max you can run for bashing - it'll be hot after running a full pack, even with a decent motor fan. For speed runs you can push it to about 2000W because you're just doing a run and then letting it cool. Above 2000W is entering the danger zone and it will go from dead cold to overheating in a matter of seconds. Not only that, the rpm of the motor is too high. 6900kv*6cells*3.7v/cell <- i'm being conservative because the current is >200Amps so the batteries will be drooping a lot. = 153,180rpm The bearings in a 3650 motor won't like being operated above 50,000rpm for long periods or about 80,000rpm for short periods. Theoretically max power is half of maximum rpm so if you had your gearing set just right you'd only get up to 75,000rpm which I guess is acceptable for very short periods. I would look for a 3650 motor in the 2500-3500kv range for 6S. That will get you output power around 2000W which is potentially still usable and should last a pass or 2 before getting too hot. You're better off sticking to a higher kv motor on 3S or 4S because you get much higher rpm at the motor for sane (1000-2000W) motor power. Longer can motors (like 3665, 3674, 4074) will handle more power, but the rpm is much lower for the same power output as a 3650, which is a problem in a TT02 where you find yourself gearing limited and must have a motor that runs at higher rpms.
  15. I have a similar LiPo alarm (on ebay as "BX100 LiPo Tester") which looks identical to that one but has a black casing. Works great! I prefer one with a plastic casing rather than just heatshrink because the balance connector on a LiPo does not have current limiting. If it manages to short out, potentially you have a fire. I have the case of mine taped as extra security against it coming apart, and it is zip tied to the battery hold down so it can't flop about in the chassis.
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