Jump to content

nbTMM

Members
  • Content Count

    248
  • Joined

  • Last visited

Posts posted by nbTMM


  1. My understanding is that aerodynamics does not scale down perfectly due to how boundary layers act on scale wings and bodies versus 1:1 vehicles. Basically, wings on scale vehicles which are profiled like airplane wings do not work as effectively to create lift/downforce compared to their 1:1 counterparts. That's why you see Lemans/'Pan' style shells with a rear 'scoop' with aggressive attack angle, instead of a separate wing with shallow attack angle and a gap between it and the body for the low pressure zone to form. It's also why RC airplanes have to be extremely light weight or travel at insane scale speeds, because their wings are not very effective at creating lift.

    I think most of the downforce on an RC car comes from it simply displacing air, creating a high pressure zone above it, which pushes the shell downwards as long as the air inside the shell is lower pressure. A big scoop on the rear creates yet higher pressure over the rear of the shell as it increases the amount of air displaced, and therefore produces more downforce at the rear, at the cost of higher drag.
    If cut out the the rear of the shell, the low pressure zone generated behind the car will suck air out from the inside of the shell and maintain a low pressure zone inside the shell (or at least lower pressure than 'outside'), therefore maintaining downforce. Undertrays/diffusers/splitters on rc cars probably create less actual ground effect under the car and instead just act to better seal up the shell, preventing air from entering the shell and therefore allowing the low pressure zone at the rear to more effectively maintain low pressure inside the entire shell. If too much air enters the shell and too little air is sucked out the back, it becomes pressurised, creating lift and the car takes off.

     


  2. Patience has definitely paid off for me when selling niche items. It only takes 1 buyer to pay the price you want and they may not be looking at the time you create the listing, so you have to wait for them. I've listed and forgot about items, and then had them finally sell 3+months later. Offer postage otherwise you are dramatically reducing your pool of interested buyers. The automatic postage calculators on eBay etc work great for this so closer buyers get cheap postage yet you don't eliminate buyers who are really far away but prepared to fork out for the postage. 

     

    • Like 1

  3. Upgraded the TT-02 fun car to a Surpass hobby 3650 4 pole 5200kV motor. On 3S lipo, this makes for a healthy 1200W mechanical output power :D. Enough to destroy and blow fully glued tyres off the front wheels, because when the front diff unloads the inside wheel spins up to 150kmh+. Thicker diff oil required. 
    vU3yl0D.jpg

    lT8uCcW.jpg






     

     

    • Like 2

  4. If you use rubber tyres, making it rwd will just make it very difficult to control. With rubber tyres, as soon as the rear breaks traction the car will swap ends, faster than a steering gyro and lots of steering lock are able to react to. With the hard plastic drift tyres, things happen a lot slower so a gyro can sense the car rotating and start steering the wheels into the slide to prevent the car spinning all the way around. Money is better spent on a dedicated RWD drift chassis if that is what you want to do, instead of modding the TT-02 imo.

    If you want to give your TT-02 more drift happy on rubber tyres without converting it to RWD and making it almost impossible to control, try stiffening the rear diff by adding AW grease, and adding stiffer rear springs and softer front springs.

    • Like 2

  5. I would say that you might need an esc fan with a 4300kv motor on a cheaper 60A esc. Many higher quality 80A and 120A ESCs would have a better chance running that motor on 2S without a fan as they have lower resistance transistors so generate less heat in the ESC. 

    If the ESC has overheat protection functionality, then it should be safe to try without the fan - worst case it should just stop running if it gets too hot. After cooling off and power cycling, it'll run again.

    Running a higher FDR will make both the motor and ESC run cooler, so could be the ticket if absolutely cannot fit the ESC fan. You can also try mounting the ESC in an unconventional position (e.g. on its side) if it achieves a lower profile. 


  6. I agree with others re: just do the bare minimum to get them running and have fun! Better performance or better control does not always equal more fun, and older Tamiya cars have a certain charm or quirkiness to how they drive (and in some cases being a bit temperamental!)

    That is not to say don't upgrade them to newer electronics (which are dirt cheap these days), but part of the fun of this hobby for me is to perform incremental upgrades and discover for myself how one part makes the car drive differently to another.

    • Like 2

  7. I would completely rule out any 1/10 road chassis based car like the TT-02 and XV-01 if "run decent on grass" is a hard requirement. In my experience, with narrow 1/10 rally tyres (like Tamiya rally blocks), you will struggle to make forward progress with <20mm ground clearance on most grass. If you have an excessive amount of motor power (>4000kV motor, 2S LiPo), you can hit the grass at speed and as long as you don't stop, keep moving, but forget that if you plan on running the silver can brushed motor. With >30mm ground clearance, things will go better but then the car will traction roll easily, and it's a bit too much droop for the drive shafts to run smoothly. A 1/10 rally car will be great on dirt and gravel, but I think you will be seriously disappointed with it's ability on grass.

    • Like 1

  8. That part is called the horn. If using a servo saver it is specific to that particular design of servo saver, e.g. Tamiya #51000 high torque servo saver. A lot of tamiya kits come with a cheaper all-plastic servo saver on the parts trees, which will be different for each kit.

    If you don't need a servo saver, you can buy sold aluminium servo horns for a couple dollars on ebay/etc.


  9. 8 hours ago, Jonathon Gillham said:

    1400mah last about 10mins - I generally feel nostalgic about this hobby but not the 10min run time

    If I get 10minutes from a 5000mAh 3S LiPo it's a good run. Guess I'm doing this hobby all wrong :lol:

    • Haha 3

  10. If you only ever intend to run them stock, then there is not much difference. 

    Some notable advantages of the TT-02 however:
    - The differential cover is split horizontally instead of vertically, so grease/fluid leaking from the differential gear over time is captured, instead of leaking onto the ground. 
    - The chassis supports square profile 2S lipo batteries without modification. TT01 requires the ribs to be cut/dremelled to fit packs other than a typical round cell 7.2v NiMH.
    - Way better aftermarket support. Aftermarket TT01 parts dried up quickly after the TT02 was released.
     

    • Like 2

  11. They are HXT connectors - prevents plugging in batteries / ESCs backwards accidentally. For inline connections there is zero chance of them exposing metal and shorting together unlike heat shrunk bullet connectors. Not pretty, but functional.


  12. Probably all the hopups trying to turn a TT02 into a plastic tyre drift car. It never handled how I wanted it to and just wasn't enjoyable to drive, probably because I didn't have the correct surface to run it on. It's much more enjoyable as an overpowered rubber tyre go-anywhere basher.   

    • Like 1

  13. From hobbyking: https://hobbyking.com/en_us/turnigy-receiver-pack-2300mah-4-8v-nimh-flat.html

    Generally with NiMH you get what you pay for however. In my transmitter I use Energizer 'recharge' AA NiMH, the made in Japan ones which are well known for being some of the best cells around. You will likely need to source them through an electronics distributor though as Energizer sell several different types of NiMH cells under similar names and appearances - the ones sold at mum and dad brick and mortar type stores are almost always crappy chinese made cells. There are also fakes being sold so avoid trying to source quality cells from places like eBay. A a low-power device like a transmitter isn't very demanding though, so likely cheap NiMHs will get you decent runtime and lifespan.


  14. I think even if you cut it and glued it back together perfectly, it would still be out of round because the tyre is going to want to maintain the radius that is was molded as. It will probably assume an egg shape not unlike your last picture.


  15. Drift car is no more. I ended up making it RWD, which required some yeah racing parts such as the aluminium steering and suspension arms to get adequate steering lock while maintaining reasonable steering lock. I decided though, that plastic tyre drifting wasn't really for me. It requires a really smooth surface like polished concrete, otherwise the 'tyres' get scuffed up too much and generate too much grip, and constantly wear into a conical shape on rough surfaces which means that how the car handles constantly changes as the tyres wear. 

    Left: drift car. Right: a new TT02 project that I'll cover at a later date.

    IR3nVyJ.jpg

    The drift car was converted back to 4WD and rubber tyres because I had way more fun with it like that. My goal with this car is to make an all-weather all-terrain car that I can beat on and doesn't require much maintenance. I always avoided running my TT02s in the rain or gravel/dirt because the tub just ends up getting drowned or filled with debris and bearings rust solid. With this car, that will change! Also, I will try to use as many stock and half-worn parts that have come off my other cars. The first phase of making it weather proof was to retro fit a set of XV-01 mudguards or wheel arch liners. This was accomplished with some aluminium mounting bars which I attached by using longer bolts at the front propjoint bearing cover, and the rear upper suspension arm mount respectively.
    Dh8jXGT.jpg

    rylB4fC.jpg

    I also made some custom side trays to block water and debris being thrown up between the chassis and body shell. These are made from FRP - actually 1.6mm printed circuit boards that I had made. I goofed some of the hole locations, but managed to salvage them by drilling some new locations. They were designed to make the chassis exactly 190mm wide to suit another project, but I cut these ones down to the same profile as the Lancia Delta Integrale shell so they aren't so obvious.
    Rxi7fNO.jpgZD84cbB.jpg

    Some closed cell foam seals the gaps between the guards and body. Just in case water does get in, waterproof electronics were installed. The ESC is a Hobbywing WP-8BL150 which is overkill but waterproof (electronics completely potted in resin) and reasonably cheap. The motor is a Trackstar 7.5t brushless which is run as sensorless, effectively making it waterproof. Due to running sensorless, the motor endbell now has no effect but I can set the timing to 26.5degrees in the ESC which makes this motor about 4400kv. Spur gear is a 61t 0.6 mod from a TT01, which if ground down slightly fits on the TT02 shaft. Pinion is 27t. The GT5 receiver I pulled apart and gave the circuit board a generous coating of epoxy resin.

    765V6Bz.jpgAOVbQNE.jpg

    lNeDRQe.jpgy2b221l.jpg

    For the steering i'm using the stock plastic parts, however with some aluminium bushings that I found in my parts box pressed into them. Together with M3 bolts that have a smooth shaft near the head, this reduces the slop in the steering a little bit. Not as good as aluminium ball bearing steering, but cost me nothing and is more resistant to water and dirt.
    The steering servo is a Goteck BL1511S brushless, which has rubber o-rings so should be water resistant even if they don't advertise it. This servo is extremely fast and quiet, but its deadband does not meet the advertised spec at 6.0V (ad: 1us, reality: >10us) so I don't recommend it. At 7.4V it is better (<3us) however I don't have any ESCs which have a high voltage BEC, and don't plan to get one anytime soon so I'll manage with the slightly sucky dead band for now. As usual I use a Tamiya #51000 servo saver and 3racing aluminium horn since they just work.
    1ys9V5Q.jpg

    Continuing the theme of using parts already on hand, I installed a 30mm motor fan using the plastic mount that comes with the TT02 kit. I opened up the restrictive grille with a dremel to aid airflow and cut away the switch mount to clear the terminals of the brushless motor. I usually use a 40mm fan with a custom mount, but thought I'd give this a try. It works well!
    8RBieI8.jpg

    Suspension was changed to ZD racing front buggy shocks all around. They are huge/long compared to regular on-road shocks. For the rear, i'm using a custom made FRP shock tower which has additional mounting holes to accommodate longer shocks, together with a 6mm spacer installed internally on the shock shaft to limit droop.
    Diffs are TB01 diffs which are cast aluminium and will take more power than the standard plastic ones. Drive shafts are metal dog bones and cups as per TT02RR - I chose these as they are more resistant to water and debris than 'CVD'/universal shafts. When they get dirty they clatter a bit, but it's better than a universal jamming up from dirt or rusting solid. Currently the rear diff is filled with 1million cst oil and the front with 100k cst oil, but I'm still playing around with weights. 
    p0zhppR.jpg

    At the front, the droop of the shock needs to be limited more because the front suspension lower ball joint and drive shafts do not support as much travel as the rear while turning. Putting 9mm of spacers internally achieved the right amount of travel but was too stiff as making the shock overall shorter pre-loads the spring. The front springs need to be softer on a TT02 to utilise the travel of the front suspension because the chassis has a rear-biased weight distribution. I ended up using a 3mm droop spacer internally and put a 6mm spacer externally. This makes the shock too long to work with my FRP tower, so I reverted to a setup I had used to run long shocks on a TT02 before - an aluminium plate which bolts to the standard plastic shock tower. 

    RJi2IW8.jpg

    The new front shocks are too big for the standard front bumper arrangement to work, but some trimming and a bolt solves that.
    HpPNK8H.jpg

    The guards and foam are really effective at preventing water and debris getting thrown directly by the tyres from entering the tub. 
    wk0nA9H.jpgcTtw5nO.jpg

    cX9pKEW.jpgCygq0mZ.jpg

    They are less effective against fine dust, or if you slide the car sideways through a deep puddle. When driving on gravel, the steering can be jammed up occasionally by larger rocks. Nevertheless, the car is definitely easier to clean after use. I have all rubber sealed bearings which I packed with wheel bearing grease (for 1:1 cars). After use I remove the battery, hose it down, shake it out and leave it to air dry - no issues yet! The side trays are less pretty after being pelted with gravel though I can't say I didn't expect that.
    fPNM7Ur.jpg3mjvNex.jpg
     

     


  16. On 9/25/2019 at 9:51 AM, BoraBora said:

    Great info, thanks, love my tt02s, which one of these motors would you reccommend to swap onto a prebuilt with the brushed setup, a 20t or a 15T, Arrma sells them for pretty cheap  https://www.ebay.com/itm/292843307820  /   https://www.ebay.com/itm/ARRMA-Mega-Motor-Brushed-15T-540-AR390031-Fast-Ship-wTrack/183672041374   , 20$, just want something a bit quicker then stock, nothing too fast,  dont want to do to much upgrading right now either just want to mainly drive and break things and upgrade on the way lol. I have a STI NBR kit with a full YR aluminum conversion i plan to build that one up with a nice brush less setup. 

    I'd go with the 15T if your esc supports it. It'll be substantially faster than the stock motor, but shouldn't push the standard TT02's drivetrain past it's capabilities. 20T will only be a little bit faster than stock, so probably not worth the upgrade. 


  17. I just drill a smaller sized hole (e.g. 4mm), then the final size (e.g. 6.5mm), with regular drill bits. I then clean the burrs with a step drill bit by hand. Press a piece of wood up against the back of the polycarbonate shell when drilling to avoid tear out. 

    • Thanks 1
×
×
  • Create New...