Jump to content

nbTMM

Members
  • Content Count

    299
  • Joined

  • Last visited

Posts posted by nbTMM


  1. 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.


  2. 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.


  3. 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.


  4. 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.
    7uZBe2Q.jpg
    yqYq9Md.jpghCekxpc.jpg

    • Like 3

  5. 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.
     

    • Like 1
    • Thanks 1

  6. 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.

    • Like 1

  7. 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 :o. 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 :unsure: 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!
    pJcbrwY.jpg1m0kxIi.jpg


     

    • Haha 1
    • Confused 1

  8. 15 minutes ago, WillyChang said:

    04m & 64dp are the biggest mixup risk :( got near equal population of each size. Easiest way to tell is nearly all my 04m are Tamiya & they're not steel. 

    They are so close (<1%) that they are effectively the same thing though. The teeth on small gears are not usually 100% accurate, they just have to be good enough. The cutting tools that create the teeth have a tooth range, so that one cutter may create the teeth on gears anywhere from 50teeth to 100t. It'll be perfect making teeth on a 50t gear but by 100t is considered just barely close enough - if you want to make a 101t gear you should get a different cutter. For that reason, the inaccuracy between two 64dp or 0.4M gears may be greater than between a 64dp and 0.4M. I wouldn't be surprised if in the industry people use the metric and imperial cutters interchangeably between similar pitches
     

     

    • Like 1

  9. You can gain a millimetre by changing bearings. If the current setup uses 4mm wide bearings, use 3mm inners and 5mm outers. There may also be scope to grind the diff cup joints to get them to sit in a further mm.

    Otherwise, yeah racing make some adjustable universals for their tt02 rwd drift kit. The universals themselves are junk (aluminium) but you can use the adjustable dogbone ends on other shafts by cutting the shaft and grinding some flats into it. I used them to make short double cardan shafts for a tt02.

    • Like 1

  10. Red triangle or red arrow indicates a towing point. Blue triangle indicates battery location. Blue triangle with a red lightning bolt indicates battery isolation switch. Red 'E' is a fire suppression system pull handle

    • Like 2
    • Thanks 2

  11. Brushless aren't that much more efficient. Brushed hits about 70% efficiency, brushless is around 85%.

    The difference in ability of the ESC to handle brushed versus brushless motor comes down to what happens when the motor is stalled, or nearly stalled. Most brushed ESCs have no idea what the motor is doing so if you ask for full throttle and the motor is stalled, significant current will flow and the ESC might not do anything about it until it overheats or the battery voltage sags too low. The stall current of a 27t silver can brushed motor is about 70Amps, which the ESC will handle for quite some time before eventually overheating.

    Theoretically the stall current of a 13.5t brushless motor is about 250Amps. However, since a sensored brushless ESC knows how quickly the motor is turning (if at all) it can reduce the duty cycle of the pulses going to the windings to reduce the current. That's why you sometimes hear buzzing and clunking sounds when a brushless motor is turning against significant resistance, because the ESC is reducing the duty cycle of the pulses to manage the stall current and therefore it's capable of dealing with more powerful brushless motors than brushed.

     


  12. I think all of them are nylon, the parts tree will tell you; "PA" for nylon, "PA-GF" for nylon with glass fibre, "PA-CF" for nylon with carbon fibre. My experience with glass reinforced nylon is that the wear resistance is excellent - the grease or oil doesn't get polluted with dust over time like the cast aluminium gears do. However, since any plastic gear can still bend, if they get put under too high of a load the two gears can be forced apart and skip a tooth, and then small pieces of the teeth can break off. 

    • Thanks 1

  13. 9 hours ago, Yalson said:

    Not sure what you mean by blowing across the paper.

    The ground effect/venturi won't make it lift as you suggest, though. The lower pressure in the expandng section of a venturi can be used for downforce, but won't make a piece of paper lift. There are other effects that will, though.

    Try blowing an air gun into a open plastic bag, or under a sheet of paper held 1cm above a table. The effect is opposite to what you'd expect. The bag gets sucked closed, and the paper is sucked down onto the table.

    You can get the same effect with a flat bottom RC car, although I think the effects of dealing with the fact that the "inside" of an RC car shell is rather leaky (wheel arches and other gaps) makes much more of a difference than ground effects alone.

    • Like 3

  14. You only 'need' to change gearing if the motor or ESC runs too hot. Otherwise, if you aren't racing it's a matter of preference. Less teeth will give more acceleration, more teeth will give higher top speed. If you labour the motor by gearing it for high speed and then running at low speed most of the time it will just run inefficiently, resulting in the electronics getting hot and the battery getting drained faster.

    A 15t brushed should turn about 30,000-35,000rpm if i'm not wrong. If the XV-01 standard final drive ratio is 8:1, at 100% rpm tamiya rally block tyres will be going about 59kmh. In reality, when actually under load you will probably only reach about 70-75% of maximum rpm so about 42km/h or so. If you put a 15t pinion in then you'd have a top speed of 30km/h and the car would accelerate faster and run cooler.

    I would order some other pinions to try anyway just in case it does run too hot on the standard pinion. There are cheap sets of 13t-17t 0.6 module pinions on ebay
    https://www.ebay.com.au/itm/M0-6-3-175mm-13T-33T-0-6-Module-Pinion-Motor-Set-Gear-For-1-10-RC-Car-Truck/333281900182?hash=item4d99263696:m:mzyWDetdZanYSm0Eigv8uHw&frcectupt=true

    Installing a 30mm motor fan will also definitely help keep the motor cool. Again, hit up ebay for "30mm rc motor fan" to find a cheap one.


  15. The quicrun 13.5t motor+esc combo is hard to beat for the price, I'd recommend that. 

    TT02B needs at a minimum the metal differentials from a DF02 to be reliable as a basher, even with the stock brushed motor. A TT02B and Arrma Typhon are opposite ends of the spectrum for buggies. The TT02B being one of the most fragile and the Typhon being one of the toughest. If you want a TT02B to handle big power (<10.5t) and larger wheels than standard, expect to upgrade almost everything in the drivetrain.

     

    • Like 1

  16. 49 minutes ago, Gazzalene said:

    If its anything like when they change food packaging, the food never tastes the same!  I would bet there is something else that's been changed!

    Well it looks like the previous black one was 27t with the timing advanced a bunch to bring the rpm up compared to a normal silver can. The new silver one looks to be 23t with mild or zero timing. Theoretically the new one should be a bit more powerful, but spin about the same rpm. It's likely that the new one is more of a generic motor so is cheaper to produce. Statically advancing the motor timing a bunch isn't usually done outside of RC because it makes the motor less efficient, so the black motor might have cost more to produce as it has non standard manufacturing.

    • Like 1

  17. A 3-cell/'3S' (9.9V) battery will definitely make the car more powerful than a 2-cell/'2S' (6.6V) battery. Just make sure your motor and ESC are rated for 10.8V (fully charged voltage of a 3s life pack). The mAh rating is indeed the capacity of the battery - more capacity = more runtime. Be aware however than if you use a 3S battery, the electronics will draw more power so a 3S 4200mAh battery will have less runtime than a 2S 4200mAh battery. Higher mAh packs also tends to be heavier and physically larger, as will packs with more cells. The nano-tech pack is physically smaller, lighter and has lower capacity. I'd say the reason for the low discharge rate (1C) is because of the low-current plug installed on it.

    All batteries are inherently unsafe, as they can store a lot of energy, and if abused all that energy can be released suddenly resulting in a lot of heat and possibly a fire. LiPos are primarily less safe than NiMH because the energy density is slightly higher (mAh higher for same physical size) and they typically have much lower internal resistance, so will happily release a huge amount of energy quickly. A LiPo pack might happily provide 500-1000Amps of current if shorted out, whereas a NiMH might only do 50-100A. Lifepo and NiMH can cause fires, but you have to try much harder. Lipo and Lifepo are more sensitive to improper charging, over-charging, over-discharging and degrade more quickly when stored for long periods at an improper voltage compared to NiMH. LiFePo4 sit somewhere between NiMH and LiPo with respect to energy density, power delivery and therefore safety. 

    Not sure what you meant by 'keeping stuff on charge isn't an option'? With LiPo you store the batteries at about 40% charge (~3.8V/cell), as this gives the longest shelf life and some buffer so the battery doesn't self discharge to 0% if storage long term (up to 1year). If a LiPo cell goes below 0% (3.0V) charge, it is permanently damaged and attempting to recharge it is risky. The car needs to have an appropriate cut-off so it stops before the battery voltage gets too low. Storing at 100% (4.2V) long term will also drastically reduce the lifespan of a LiPo.
    When it's time to use it you put it on the charger and bring it up to 100% which takes about 30mins to an hour for most batteries. All LiPo battery chargers automatically stop charging when the battery hits 100% (4.2V/cell). Balance charging is typically performed to make sure that all the cells in the pack are charged to equal voltage and no single cell is brought above 4.2v which could damage it.
    After use you should immediately charge (or discharge) the LiPo to the storage charge of 3.8V/cell and put away in a fire safe bag. Typically LiPo fires only happen if the battery is charged improperly (non-balance charger), charged or discharged at an excessive rate, or is continued to be used after being physically damaged or after accidental over-discharge. Because the risk is elevated when charging a lipo, you should never leave a charging lipo unattended.

    Technically Lifepo batteries should the treated the same as lipo to ensure maximum lifespan and safety, the voltages of interest are just 2.5/3.3/3.6 instead of 3.0/3.8/4.2. Using a Lifepo in a transmitter is somewhat at odds with the whole storage charge philosophy so I'm not sure how we ended up with lifepos being primarily sold for RC transmitters. I use NiMH in my transmitter.


    When treated properly and put in a fire safe bag while charging/storing, the risks of lipos are minimised. The exact same battery technology is used in phones and laptops, the only difference is that those batteries permanently have battery monitoring circuitry attached to them to prevent them being charged/discharged improperly, and people generally don't often crash their phones/laptops at high speed, physically damaging the battery. With RC batteries the responsibility is put onto the user to ensure that the battery isn't charged/discharged improperly and inevitably people get it wrong and cause fires.

    NiMH are generally much more tolerant of abuse (over charge, over discharge, stored at 100% charge) so are a better option if you don't have time or patience to charge/store batteries properly. They however self discharge at a much higher rate so you should charge them fully every few months to prevent them over-discharging while sitting on the shelf and degrading.


  18. The silver kit motor is 27turns. The less turns a motor has, the faster and more powerful it is. WP-1060 brushed can handle down to a 12turn motor on a 7.2V battery. Depends what your definition of 'good performance' is as to if the kit motor will be adequate. A 12T is quite fast for most people - I would try the kit motor first, then upgrade later if you feel the need for more power. 


  19. Silicone spray is just silicone oil mixed with a solvent in an aerosol can. It will achieve the same 'wet' look as rubbing silicone oil on the parts, but the solvent in the spray can attack the surface of certain types of rubber and plastic, making them appear milky or hazy when the silicone oil eventually wears off.

×
×
  • Create New...