nbTMM

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Everything posted by nbTMM

  1. Taking a break from electronics to work on mechanical stuff again. The plan was always to do some de-monsterfication and step 1 to accomplish that was to get some more realistic wheels and tyres. The standard tyres were too big and wide anyway - the new shocks wouldn't fit between the chassis and rear tyre if I mounted them the same way as the front. The front tyres could also rub the body on full lock full compression (more about the body in a later post ;)) Enter RC4WD 1.9" steel 'wagon' wheels and 4.19" Goodyear Wrangler MT/R tyres: I've wanted to do a build with these wheels ever since seeing some on a CC-01. These are called 'sunraysia' wheels in Australia and are hugely popular aftermarket off road wheels. The 4.19" tyres are small enough to fix the fitment issues and monster truck look, but still big enough that they don't look weird with the amount of lift that the bruiser has. The wheels come with hubs that accept a standard 5mm shaft and pin (left). To mount these wheels on the bruiser, I'd need the hex hub for the wheels (right) and an RC4WD bruiser hex conversion kit. For whatever reason, the hex conversion kit came with bolts that were 2mm longer which looked a little weird as too much thread stuck out of the wheel nuts. The shorter bolts that came with the wheels had heads which were just a hair too big for the hex hub, causing them to bind on the hex adaptor, so I ground them down to suit. This is the standard 3-lug bruiser hub, which obviously won't work with the RC4WD wheels. Up front, the hex conversion kit (left) consists of a wheel axle which is basically identical to a standard TG10 wheel axle, except that it has a black finish, and a 12mm hex adaptor which has a skirt to accept the large wheel bearing. Both bearings are reused from the standard hub setup (right). The TG10 style axle simply inserts into the steering knuckle from the rear, then the large bearing and drive pin are installed onto the outside of the knuckle. The hex adaptor rides on the axle/pin and outside of the bearing. The inner race does not touch the hex adapter. If you're familiar with 1:10 TC cars then the outer bearing is the opposite to normal - the inner race is stationary while the outer race rotates. Upon installing the wheel and tightening down the wheel nut, all was not well. The bearings bound up a little so the wheel was hard to turn. Usually you design for a loose fit and add shims to tighten it up until it is just right. Here it was already too tight with no shims, so the only easy solution was to install a thinner bearing. I first tried replacing the inner 10x5x4mm inner bearing with a 10x5x3mm, however the engagement with the dog bone end on the driveshaft was marginal so I decided not to go that route. Instead I changed the 16x8x5mm outer bearing for a 16x8x4mm. This solved the binding issue. Three 0.2mm shims between the hub and bearing had it running just right. The other side required the same treatment however with only two shims.
  2. nbTMM

    TT02 vs TT01e for average use

    The TT01 has cast aluminium diff gears if i'm not mistaken. While they may be stronger in the short term (support a higher power motor), in the long term they will probably wear out faster than the glass-fibre reinforced ABS plastic gears in the TT02. Cast aluminium gears create aluminium dust which pollutes the grease/oil and turns it into a grinding paste which only increases the rate at which the gears wear. They require more frequent servicing to clean and replace the polluted grease/oil, especially when they are new and 'wear in'. The TT02 glass-fibre reinforced gears don't appear to create any appreciable dust or have any wear from my experience. The TT02RR I have has cast aluminium diff gears and the diff oil does get polluted with alu dust over time. Haven't had any issues with gears or shafts breaking in my cars: one car has a 7.5t on 2S, other car has a 21.5t on 3S. The plastic TT02 driveshaft is perfectly fine, I wouldn't even bother upgrading it. I run aftermarket hardened alu pinions and nylon spurs - the aluminium spur provided in the kit is known to turn into aluminium dust at an alarming rate. I tossed the standard motor gears very early on because I wanted the cars to go a lot faster than standard. Excepting aftermarket parts, I've needed to replace the upper TT02RR suspension arms, which are a far more fragile design than the normal non-adjustable TT02 arms. Also, I've replaced the front suspension arms and plastic ball joints after 20-30 packs or so because they wear out and become sloppy at the ball joint. They were still usable at that point but had enough slop that they were making the car noticeably less stable at 50kmh+. A few wheel bearings have have died (gritty or completely locked up) after crashes at 50kmh+.
  3. nbTMM

    Do touring cars have any front kickup at all?

    Kick-up is basically synonymous with caster for TCs because the track is (usually) perfectly smooth. Having independent adjustment of kick-up and caster is only required if you want to alter the jumping/landing/bump and cornering behaviour of the car independently. Tuning of suspension in TCs is more focused on weight shift during cornering than handling bumps in the road.
  4. nbTMM

    The Day eBay Killed RC

    Ever since ebay introduced automatic bidding, sniping software is moot because whoever puts in their highest maximum bid will still win the auction. If I bid a maximum of 150 when the auction starts and then you bid a maximum of 148 just seconds before it ends, I still win. The only way for you to win is to bid more than 150 any time before it ends. It's not unreasonable to bid in the last <5 seconds without sniping software anyway. The only advantage is that a few seconds isn't long enough for the average bidder to change their mind about how high they're willing to bid, and manually raise their maximum bid after seeing that the bids have gone above their maximum.
  5. Yeah racing 4.8mm rod ends are stout, but far more bulky than tamiya 5mm ones and take about 3x the force to get on/off the balls. The hole in the top has the advantage that you can unscrew the ball without removing the rod end if the ball is hex keyed. Disadvantage is that it lets dirt in. These: https://www.ebay.com.au/itm/Yeah-Racing-BN-0011-Nylon-Ball-End-Set-3-8-4-8-5-8/361763110989?hash=item543ac3004d:g:Ki4AAOSwGPNcUEWQ&frcectupt=true For turnbuckles just take a gander through yeah racing or 3 racings websites and see if you can find something that fits the bill or can be cut to length, then search ebay for it. If you need the ultimate durability and lightness then don't do this as most of the cheap ones are fairly low grade steel, are heavy and bend easily.
  6. nbTMM

    The Day eBay Killed RC

    Also, allegedly the GSP warehouse selectively open and re-pack items where they feel they can reduce the dimensions of the package to save cost. If it's a fragile item that requires significant packing material to protect it, avoid GSP at all costs because they might remove all the packing material and shove it into a smaller box.
  7. nbTMM

    Gear ratio

    unloaded wheel speed (kmh) = V * K * Tpinion / Tspur / Rdiff * Wdia * pi * 60 / 1000 Where: V = battery voltage K = motor kv Tpinion = number of teeth on the motor pinion gear Tspur = number of teeth on the spur gear Rdiff = the differential gear ratio Wdia = the wheel/tyre diameter in meters pi = 3.1415 As an example we can calculate it for my TT02 which has a 5130kv brushless motor, 2S Lipo pack, 61tooth pinion gear, 69tooth spur gear, and touring car wheels/tyres which measure about 65mm diameter. Therefore: V = 8 <---- 4 volts per cell is a good guesstimate for a freshly charged lipo, accounting for some voltage sag under load K = 5130 Tpinion = 61 Tspu = 69 Rdiff = 2.6 <----- this is the standard diff ratio for a TT02. Unless you use over/under-driven 'drift' spools with different numbers of teeth of the diff crown/pinion gears, it will be 2.6 Wdia = 0.065 unloaded wheel speed (kmh) = 8 * 5130 * 61 / 69 / 2.6 * 0.065 * 3.1415 * 60 / 1000 = 171kmh So if I hold the car in the air and floor the throttle the wheels will spin at 171kmh. Will the car actually go that fast? No. In reality the fastest it's gone on GPS is 100kmh. This is because DC electric motor power peaks at half the unloaded rpm.so the motor power is starting to reduce when the car exceeds about half of the unloaded speed, ~85kmh. At some point, the amount of power the motor is producing will become exactly equal to the forces of aerodynamic drag and friction from the drivetrain and the tyres rolling on the road. At that point, the car will not go any faster and you want this to occur where motor power is maximum to achieve the fastest possible speed for your setup. You can calculate drag and motor power and so on, but honestly the simplest way to work out if you have the right gears is just to do a speedrun and then compare the actual top speed to the calculated unloaded speed. Since my car already goes faster than 85kmh it means that I'm undergeared - the motor power has already reduced somewhat when it hits the maximum speed of 100kmh. I could put a pinion with more teeth and/or a spur with less teeth to achieve an unloaded speed closer to 200kmh, so motor maximum power would occur around 100kmh where my car currently tops out. Unfortunately I physically can't fit a bigger pinion or smaller spur so the only solution for me to go faster is to get a motor with higher Kv, or wheels/tyres with a larger diameter. A more aerodynamic body shell might get me a few kmh too. Similarly, if my car topped out at 60kmh with the current setup it would mean that i'm overgeared - the motor wouldn't be reaching maximum power before the effects of aerodynamic and mechanical drag became too much. In that case, a smaller pinion and/or larger spur would be required to go faster. If it topped out at exactly 85km/h the gears are probably just right and the only way to improve it is a more powerful motor, more aerodynamic shell or higher voltage battery. Be warned that running your motor full throttle for long periods near half it's unloaded speed or less will cause it to get very hot! Most RC cars need to be undergeared to keep the motor rpms up and therefore motor temps under control. The gears that achieve your maximum top speed will generally not allow you to run the car for very long before overheating the motor/esc. The TT02 is very undergeared out of the box (22t pinion 70t spur) so you will find that the actual top speed with those gears is very close to the unloaded speed. Effectively the top speed out of the box is more limited by the gear ratio and kv of the motor because it's going so slow that aerodynamics and motor power are barely a part of it.
  8. nbTMM

    WR-02CB straight steering

    I actually find that some amount of slop/flex in the steering is required to track perfectly straight without having to constantly re-trim the steering servo. This is because no matter how good your steering servo and servo saver are, they will never return to exactly perfectly centred after performing a turn. The trick seems to be to make sure that the slop is only in the steering axis (toe). Slop that can cause significant changes to caster, camber, offset, or shift the entire wheel forwards and backwards in the chassis, seems to hurt stability. The rear wheels obviously should not have any slop in the toe axis. A little slop/flex in the steering, when combined with positive caster will allow the wheels to self centre even if the servo/servo-saver are doing their best to steer slightly off centre. More caster = more straight line stability. After removing unwanted slop from all four wheels, it's the single most important thing to tweak for straight line stability on a flat road. Note that increasing positive caster increases oversteer when turning due to jacking forces which unload one of the rear wheels - when you turn the wheels with a lot of caster one wheel literally gets lifted up and the other forced into the road, which changes the weight distribution across all four wheels. I'm not familiar with the WR chassis but on the other tamiya chassis I've used the bump steer was far from optimised. As far as I know, in a double wish bone suspension you want the the tie rod to be as close as possible to the geometry of either the upper or lower arm to minimise bump steer. Looks like they are drooping down on an angle with respect to the wishbones in the above picture - that will probably give more bump steer than if they are parallel with the wishbones. Are the tie rod ball ends supposed to be on the top side of your knuckles? You can space the ball joints up/down as required to improve the bump steer with washers, or if they need to be spaced a lot I use brass standoffs (below photo). If you increase caster, you will need to space the ball higher off the knuckle end to correct bump steer. Note the tie rod and upper wishbone/arm being parallel. Personally I've never noticed any improvement in straight line stability by toeing in the front. Slight toe out produces sharper corner turn in so I usually adjust the front to either 0 toe or slightly toe out. Toeing in the rear wheels produces a noticeable improvement in straight line stability on my cars - just don't go too crazy (>3deg) with it or you'll scrub speed and wear out tyres.
  9. nbTMM

    The Day eBay Killed RC

    The ones that list 2nd hand items for more than new are dreamers. Any buyer with a brain will do some research on the value of an item before buying second hand. The fact that the listings are still running means that no one who has seen it is willing to pay the asking price... As far as selling on ebay I've only had positive experiences. Describe the item accurately, provide good pictures and there should be no reason for a buyer to give you the run around. Don't start an auction at a price you aren't willing to sell for. More often than not you will get a better price with a 'buy it now' listing instead of an auction but sometimes you will have to wait for the correct buyer to come along. A lot of people don't want to have to wait a whole week to have a punt at an auction and then be outbid. If it's buy it now it's theirs immediately and they are willing to pay a premium for this convenience. Always offer postage if possible. Again, people are willing to pay a premium if the item can be posted because they live in a remote area or don't have the time to go and pick up the item. If you only offer pickup you are drastically reducing the number of interested buyers. Some times I've listed an item for over a month before the right buyer came along and paid my asking price. Plenty of people probably saw my listing and thought I was dreaming but in the end I found a person willing to pay my price. For buying, if it looks too good to be true it probably is. If the seller doesn't list it as working perfectly, expect something to be not quite right with it. It's also worth firing the seller a message to query them about their item if the listing is vague - if they provide better photos/description via private message that puts you at a competitive advantage over everyone else who comes across the vague listing and decides that it's too risky to purchase. Other times I've bought items with totally vague listings because everything appeared to be there in the photo and the price was dirt cheap buy it now. So cheap that even if I had to fix it I'd still be in front by a fair bit. Plenty of those times, the item turns up and it is mint! The few times I've been burnt doing that have been more than made up for all the times I bought something very cheaply and it turned out to be as-new or easily fixed and I've moved it on for a massive profit. If you want a deal on ebay you need to save searches and enable notifications so when someone does list what you're looking for at a reasonable price you can buy it before other people who know what it's really worth snap it up.
  10. A little driveway run to test out the electronics - it's getting there! This is still a bit too fast to be realistic. The torque limiting doesn't work 100% as expected - I think the TBLE02S has it's own throttle curve or does some kind of rudimentary torque limiting at low rpms because it seemed to have too little torque down low and too much up high. I turned up the torque at low rpms to make it driveable for now. More investigation required.
  11. Front shock mounts are complete (until I decide to build something better/cleverer, which likely won't ever happen ). The white plastic parts flex a bit due to the torsional load, it'll be fine... I got rid of the small leaf spring because it was just too stiff when the suspension was more than 50% compressed. The shocks have the softest springs installed. Bash plate installed: Flexin':
  12. nbTMM

    replacing an ESC connector safe?

    The main risk is the tape coming off, tearing or wearing through and allowing the exposed metal connector to short to another exposed wire/connector. A short could damage your ESC, battery and/or the wire could get very hot, melt or start a fire due to a huge short circuit current flowing in it. I would use some thicker tape like electrical tape, duct tape or gaffer tape rather than the thin sellotape. A neater solution than tape would be to slip some heat-shrinkable tubing over the connector and shrink it down with a lighter or hairdryer. The tubing is also thicker so it provides better resistance to abrasion. Buy the size of tubing that just barely fits over the connector in it's un-shrunk state. A few messy strands of copper won't hurt anything, as long as they are inside the insulator and the wire is securely crimped and/or soldered in the connector so it can't be pulled out.
  13. nbTMM

    Quietest ESC / Motor combo?

    My TBLE02S whin This. If you can find one with 16kHz or higher drive frequency then the high pitched whine from the motor when at low throttle will be inaudible unless you have very good hearing! Both my TBLE02S and Trackstar GenII 120A escs must switch at only a few kHz because they emit a few kHz tone from the motor when at low throttle. The disadvantage of higher drive frequency is slightly lower efficiency of the ESC which will make it run hotter (probably by a negligible amount).
  14. More progress on software today. This might be over the heads of non-engineers however it was a necessary step to work out how to implement a torque-limiting algorithm to make the electric motor behave like an internal combustion engine. Below left we have the typical torque vs. rpm curves of a DC motor for various throttle positions. Below right we have the throttle signal vs. rpm without any torque limiting active - if we apply 50% throttle at the transmitter, the ESC receives 50% throttle regardless of motor rpm. Pretty straight forward stuff. Below left we have the torque vs. rpm curves that I want the motor to have to mimic an internal combustion engine. I constructed them from linear segments as it simplifies the algorithms/code to implement them. Maximum torque occurs around the middle rpms and there is a drop off in torque at low and high rpms. Also, at low throttle positions the motor has a powerband that extends up to much higher rpms than normal for a DC motor, making it behave more like an internal combustion engine which does not experience the effects of back-emf. Note that all the curves just have to fit within the triangle made by the 100% throttle curve in the previous graph. This is because we can always apply up to 100% throttle signal to the ESC to produce the desired torque, even if only a very small % of throttle is being applied at the transmitter. The reason for choosing a powerful motor now becomes apparent as the bigger the triangle the more flexibility we have in drawing curves which have more torque at higher rpm versus lower rpm. On the right we have the throttle curves that are needed to implement the torque curves - note how when a constant 50% throttle is applied at the transmitter the throttle signal going to the ESC varies from ~10% to ~75% depending on the rpm of the motor to achieve the desired torque. The result of all this is that I now have a set of equations which take the motor rpm and transmitter throttle % and calculate the throttle % that should be sent to the ESC. Simple!
  15. First untethered drive. Needs tweaking to smooth out the shifts, though half of the problem is probably the untamed fury of the 13.5t
  16. Another demo with 3 gears, a timeout period after each gear change and throttle blip/cut between gears. It isn't the best demonstration because with the wheels in the air as soon as it upshifts from 1st to 2nd it wants to upshift again to 3rd because the motor speed hasn't dropped - the wheels just speed up instantly. Same thing when downshifting. It'll work properly when it's actually driving, you get the idea though. Another to-do that I forgot: -Alter the shift points when at partial throttle so it cruises with lower motor rpm and downshifts if you floor the throttle.
  17. Got the motor rpm measurement working on the arduino today. It's measuring both rising and falling edges of the hall sensors on all 3 motor phases, so there are 6 counts per revolution. It calculates the rpm based on a rolling average of the counts in the last 0.13seconds, which results in a pretty accurate and responsive rpm measurement (blue trace on oscilloscope). Quick demo shifting between 2nd and 3rd gear only (yellow trace on scope showing gearbox servo signal): Currently it isn't doing anything to the throttle signal, just passes the incoming value straight through to the ESC so the gear changes are jerky. It shifts up when the motor rpms exceeds 58% of the unloaded motor rpm and shifts down when the motor rpm is below 44% of the unloaded motor rpm. The former is determined by the graph below which shows the torque vs rpm curve at the wheels for the bruiser ratios, assuming the torque curve of an electric motor. Under acceleration we want to select the gear that provides maximum torque at a given rpm. Conveniently this occurs around 58% of the unloaded motor rpm at the crossover between 1st/2nd and 2nd/3rd gears for the bruiser. The rpm where a downshift occurs is subjective - it needs to be lower than the upshift point to provide hysteresis otherwise it would constantly hunt back and forth between gears when you're cruising at a speed around the shifting point. I set it to around 75% of the upshift point for now. To do: -Add a brief timeout period after each gear change so it doesn't change gears again immediately before the motor rpms settle in the new gear -Override ESC throttle signal and apply correct amount of throttle to synchronise the motor rpm to the next gear -Reduce ESC throttle signal while braking in 1st and 2nd gear to match 3rd gear -Don't attempt shifts while braking -add code to select gears manually or enter automatic/'D' mode, according to auxiliary receiver channel(s) -implement motor torque limiting/shaping, controlled by auxiliary receiver channel(s) -implement a way of calibrating the servo end-points and detecting unloaded motor rpm with hardware (buttons, leds), instead of entering numbers directly into the arduino code -Miniaturise the hardware!
  18. nbTMM

    Best esc for 6.5t motor

    A quicrun 6.5t as in a 540 size motor? That's pushing it on 3S. With any sane gear ratio it's going to be on the verge of overheating with 3S even with a decent fan. To run a 6.5t on 3S reliably you need about a 200A ESC and a powerful motor fan, then adjust your gearing to keep motor temps under control. On 4S don't expect anything more than a single speed run before you need to stop and let the motor cool off. 5S+ is instant meltdown territory. If you want more power you need to look to a physically larger motor for reliability.
  19. I think it is possible to select 1st gear 2WD and 1st gear 4WD independently with careful EPA setup so the plan is to be able to configure the 3-position switch on the transmitter which is currently used to shift gears, to one of two modes. One mode would select between 1-4WD, 1-2WD and 'D' like a conventional automatic gearbox where you use D for driving around at speed and 1-4WD and 1-2WD for crawling. Another mode would have 1-2WD, 2-2WD and 3-2WD, allowing somewhat 'manual' selection of gears with the benefits of smooth gear changes by having the electronics do rpm-matching on gear changes. No gear changes, but they produce maximum and constant torque (electronic limited) from 0-50mph or so. Above that torque falls off almost linearly just like an RC car.
  20. We have? It says that "aftermarket internal gears that fit in stock Tamiya gearboxes and on stock gear shafts are also allowed". By drilling a tamiya gear, it has become an aftermarket gear. Though, I think the line should be drawn at regular pinion/spur gears with a grub screw or bolt hole pattern. If it's a tamiya-specific gear (e.g. a gear in a Bruiser 3-speed transmission) then it shouldn't be allowed to be replaced with an 'aftermarket gear' since it will almost certainly have to be custom made to suit and that's outside the capability of most members. Imo if you're modifying an existing gear (tamiya or otherwise) by drilling the bore or bolt pattern to be the same as a regular pinion/spur gear that you could find off-the-shelf then that's just being thrifty. Would also be good to have some clarification on the yeah racing TT02 mount (which almost everyone in this thread would be using if not using 0.6mod gears) and also aftermarket diffs which are TT01/TT02 specific
  21. Doesn't appear to be anything special about the standard pinion though? How's drilling the standard one any different to finding an aftermarket one that would fit the bill?
  22. nbTMM

    Environmental Impact of our hobby.

    Sifting past the tinfoil hat sceptics with inflated numbers we find this: https://www.bgc-jena.mpg.de/bgc-systems/pmwiki2/uploads/Site/sanderson_1997.pdf 2% meanwhile, atmospheric CO2 has increased more than 33% in the past 100 years. Something tells me termites aren't to blame for climate change. I don't know if increasing greenhouse gases are solely to blame for climate change or if humans are 100% to blame for either. What is undeniable is that climate change is real, and humans are definitely responsible for exponentially increased gas emissions and hard waste in the past 100+ years. It would be a good thing to at least try to eliminate our potential contribution to the problem.
  23. nbTMM

    Environmental Impact of our hobby.

    In Australia it seems that the process goes that they illegally stockpile large amounts of recyclables at a holding yard until a fire mysteriously starts and destroys it all.
  24. nbTMM

    Environmental Impact of our hobby.

    The same argument could be made for standardising parts in internal combustion powered vehicles. To some degree it does already happen with multiple models and even car makers sharing the same engine and chassis designs. Ultimately logistics and marketing gets in the way and there is the necessity to design bespoke parts. With regards to standardising electric motors in 1:1 cars, even that idea has been turned on it's head recently as Tesla used a totally different brushless motor architecture (reluctance motor) in the Model 3 vs the previous models (Model S, Model X) which used induction motors. They claim that the different design requirements meant that an induction motor wasn't suitable for the Model 3.
  25. nbTMM

    ESC fans on run time

    Most fans draw 0.2-0.3A. A motor that needs cooling is drawing 20A+ most of the time. So, the fan is robbing perhaps 1% of your runtime. The wilder the motor setup, the more a fan helps and the more insignificant its power draw becomes in the scheme of things.