Jump to content

nbTMM

Members
  • Content Count

    291
  • Joined

  • Last visited

Everything posted by nbTMM

  1. C ratings are marketing bs for the most part. All they really ascertain is that one pack with a certain C rating from a particular manufacturer isn't as good as another pack with a higher C rating from the same manufacturer. In the following link is some real world testing, showing that some batteries marketed as 70-100C can't even do 35C with a reasonable voltage drop, while the best packs around can do about 50C max. Funny that the four packs that passed the 50C test were rated 65-75C, and most of the packs rated >75C performed very poorly. Goes to show that most of the vendors trying to sell you a >75C pack either have no idea what they are selling or figure that they can pull the wool over the eyes of their customers. https://www.rcgroups.com/forums/showpost.php?p=42381735&postcount=7579 Turnigy packs seem to do consistently well in various 3rd party testing, and their Graphene packs are top tier in the above test. Venom and Gens Ace seem like good quality batteries from what I've seen, but are a little overpriced (at least in my part of the world). Maxamps and SMC are bottom tier rubbish with a lot of marketing hype - avoid at all costs. That said, unless you run a fairly 'hot' motor or are a super competitive racer, you don't need much C from your battery. Most RTR setups are lucky to demand more than 20C. That's why the more powerful RTR cars move to more cells and lower kv motors - it allows the manufacturers to put more power into a car without requiring more current from the batteries. So customers can put trash batteries in them without taking a large hit to performance or puffing batteries. On the other hand if you are running a 7000kV motor and 120A esc in your 1/10 touring car then a quality battery capable of 30C+ may help. A pack being able to perform at extreme levels, even if your car doesn't need it to, also speaks volumes for the ability of the manufacturer to source quality cells and manufacture the packs properly, which could lead to longer lasting and safer packs.
  2. The drawbacks of the TT-02 chassis become much less apparent on loose surfaces. I would just buy another, set it up with CVA shocks, raised ride height, sealed bearings, rally blocks, a fabric chassis dust cover and send it... Running the same chassis as your friend could also be more fun than running two different behaving chassis together.
  3. The ESC advertising literature and/or downloadable user manual will tell you what cutoff voltages you can program in to it. If it doesn't have the ability to program the cutoff voltage, chances are it is unsuitable for LiPos. Some ESCs have you set the cut off on a 'per cell' basis and automatically detect how many cells there by measuring the battery voltage at turn on. Other ESCs require you to set the overall voltage for the pack. Both do the same thing however as the ESC can only monitor the voltage of the whole pack, not individual cells. Setting the LiPo cutoff voltage is probably the single most misunderstood part of safe usage of LiPos. 3.0Volts is the absolute minimum you should ever discharge a LiPo cell to however if you have a 2 cell pack that does NOT mean that you should set your LiPo cutoff to 6.0V. This is because the cells in a multi-cell pack are never perfectly matched, so if you set the cutoff to 6.0V, one cell would be >3.0V and the other <3.0V which is no good. To understand what is a reasonable cutoff voltage you must first understand the relationship between voltage and the state of charge of a battery. It is non-linear and goes something like this: >4.2V - permanently damaged, possibly unsafe to continue using, dispose of battery appropriately. 4.2V - 100% charge 4.0V - 80% charge 3.8V - 40% charge 3.7V - 20% charge 3.6V - 10% charge 3.0V - 0% charge <3.0V - permanently damaged, possibly unsafe to continue using, dispose of battery appropriately. I would set the battery cut off to 3.5 or 3.6V per cell. So for a 2S battery you program your ESC cutoff to 7.0-7.2V or 10.5-10.8V for a 3S pack. As you can see from the above, once a cell dips below 3.6V, it is over 90% discharged anyway. This gives you about a 10% safety margin in matching between the cells in the pack, so if the pack advertises that it is 5000mAh but one cell happens to be 5200mAh and the other 4700mAh you will still be OK. When the ESC cutoff kicks in at 7.0-7.2V, although your underperforming 4700mAh cell will be lower in voltage as more % of it's capacity has been spent, it should still be above 3.0V. Most reputable brand packs will have cells matched to better than 10%. Setting your cutoff lower than that won't give you appreciably longer run time and greatly increases the risk of over-discharging and damaging one of the cells in the pack if the capacity of the cells are not matched to better than 10%. If you have a very powerful motor, this can cause the battery voltage to sag under load and prematurely trigger the ESC cutoff. If you consistently measure your pack at say 3.8V per cell after cutoff is triggered, then maybe you might (with caution!) set your cutoff 0.2V per cell lower to compensate. You should check the cell voltages at the end of each run to keep an eye on how your pack is doing as some cells decrease in capacity faster than others as they age. A perfectly matched pack may no longer be perfectly matched after you've cycled it 50 times. If you notice any cells getting lower than 3.2V by the end of the run, consider increasing your ESC cutoff voltage, or retiring the pack as the matching between cells is becoming too poor for the pack to be serviceable. Storage charge should be about 3.8V per cell, or about 40-50% charge. LiPo cells degrade/age faster when stored at 100% charge . Storing at 40-50% gives longer lifespan and reduces the risk of fire as there is less energy to fuel a runaway discharge event. It also leaves enough charge so that the pack can sit on a shelf for a long time (at least a year) before it self-discharges all the way to 0% and becomes unusable. A charger with a discharging function can be useful if you charge a battery and then decide later not to run it, or your car breaks down mid-run and leaves the battery mostly charged. Otherwise you can get away with a charger that has a storage function but can only charge - run the battery down in the car and then charge it back up to storage and put it away. I charge/discharge batteries just on the bench in the open but always supervised for the entire charge. My theory is that if it's going to smoke up on the charger it's better for me to notice it immediately a few metres away and/or set off my smoke alarm. Don't be lazy and store batteries completely discharged or leave them installed in cars. Let them cool for a bit if they are hot, then do a storage charge and put them away in a fire bag. It is however better to put away a completely discharged battery and do a storage charge later if you don't have the time to be supervising an immediate storage charge. The golden rule is never leave charging batteries unattended. Fire bags are not as good as you being there to pull the plug if things go bad.
  4. If it's for bashing I would stick with a sensored setup as they work better if you spin out and stop often. Sensorless systems will hesitate and cog every time you get going from a stop, and they freak out more if the car starts rolling backwards - most will just wait until the car rolls to a stop before attempting to power forward again. If you always keep the car rolling forward a sensorless setup can however be just about as smooth as sensored. For ESCs from Hobbywing the 1/10 scale sensored options are QuicRun 10BL60/10BL120 or one of the XeRun XR10 variants. The 10BL120 will be plenty fine for bashing with a ~7.5t motor. The extra features of the XeRun are really only necessary for racing. For motors stick to 3650/3652/3654 (a.k.a. '540') size sensored motors. Anything from Hobbywing, Surpass, Trackstar, LRP (to name a few) will be fine - just buy whatever is cheapest imo as sensored 540 motors are standardised so any brand motor will work with the hobbywing esc. The power the motor makes is inversely proportional to the number of turns/winds. Below 17.5t is a substantial increase in power compared to a silver can. Roughly: Silver can = 70Watts 17.5t = 190Watts 13.5t = 250Watts 10.5t = 320Watts 9.5t = 350Watts 7.5t = 420Watts 5.5t = 500Watts LiPo batteries will be necessary below 17.5t. Kv depends on the sizing of the rotor and how the motor is timed therefore a 7.5t motor from one manufacturer may have substantially different Kv to a 7.5t from another manufacturer, but they should be similar in power. Therefore higher Kv does not necessarily mean it is more powerful. Some manufacturers don't list how many turns a motor is so you may have to guess what it is based on similar Kv motors from other manufacturers or if a power figure is given in the datasheet for it. Keep in mind also that a silver can is effectively about 2500kV so if you don't change your gearing, a 5000kV motor is asking for the car to be driven twice as fast to avoid running hot. If you aren't altering the gear ratio and plan to run the car in confined areas, a 3500-4000kV motor might be a safer bet.
  5. I've modified this type of Traxxas slash cover for my TT-02s (cut and re-sewn to reduce the length). Would probably work well for a DT-02 too. https://www.amazon.com/Raidenracing-Chassis-Traxxas-Original-Non-LCG/dp/B072KZ57T7/ref=pd_sbs_21_t_1/144-4080382-9035843?_encoding=UTF8&pd_rd_i=B072KZ57T7&pd_rd_r=d2b62ca3-6a5c-40ee-9427-805fbee03c5d&pd_rd_w=1iL9c&pd_rd_wg=QOCVD&pf_rd_p=5cfcfe89-300f-47d2-b1ad-a4e27203a02a&pf_rd_r=X0HWS4F6DDZ03WGC3MW3&psc=1&refRID=X0HWS4F6DDZ03WGC3MW3
  6. With brushless power, RWD isn't easy to control on dusty or bumpy surfaces. If you give it too much throttle the rear can break traction and the car swap ends in the blink of an eye. FWD will tend towards understeer if you give it too much throttle so it is a little easier to manage. 4WD can go either way and becomes highly dependant on the differential setup. With a tighter (thicker oil/grease or lock block/spool) front diff it becomes more FWD biased, with a tighter rear diff it becomes more RWD biased. And then you even play with one-way differentials to achieve even more interesting handling traits.
  7. You can do a lot better for not much more. Look into Flysky/Turnigy GT5
  8. Bricklink.com - the prices here are however more competitive since everyone knows what sets are worth. I don't know about Ireland but in Australia sets go for way more than bricklink prices via eBay. You are best off selling each one individually and offering postage rather than as bulk lot. Take good photos, add an accurate description and set a price on the higher end of Bricklink used prices - in 1-2 months it'll be sold.
  9. 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.
  10. 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.
  11. 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?
  12. 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.
  13. 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.
  14. 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.
  15. 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!
  16. 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.
  17. 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.
  18. 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.
  19. 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.
  20. 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.
  21. 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.
  22. 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.
  23. 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.
  24. Get a hard case pack. Most 2S hardcases which are 25mm tall will fit in a TT02. These are good for anything up to a fairly moderate brushless setup https://hobbyking.com/en_us/turnigy-4000mah-2s-30c-hardcase-pack-roar-approved.html
  25. Had a brain fart and managed to connect a 3S LiPo to a NiMH battery briefly instead of an ESC I was testing on the bench . Luckily one of the batteries was a NiMH with a tamiya plug and adapter, which probably helped limit the current, and I didn't push the connectors home because of the sparks. Still, the current was high enough to blast chunks out of the contacts. Replaced the connectors and both batteries seem fine A lesson to never have more than one battery out at a time if you don't have plugs that are keyed to prevent that situation!
×
×
  • Create New...