nbTMM

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Everything posted by nbTMM

  1. Firstly, lets address the elephant in the room: this isn't a genuine Bruiser, but the chinese HG P407 clone. Tamiya diehards please don't grill me too much, hopefully the amount of other genuine Tamiya gear I own makes up for my sinful purchase . The main reason (other than the price) that I went for the P407 is for the almost completely metal drive train and because I plan on bashing it and as the thread title suggests, shifting gears on the fly (there will be an electronic gearbox controller, eventually!). If I rash up the shell or grenade the gearbox, I won't feel so bad as replacement parts are dirt cheap. I was also curious about the build quality of the clone. The aim of the build is to make something which drives as scale as possible, but not neccesarily look as scale as possible. It should accelerate and handle like a 1:1 version. Everyone is probably familiar with the way electric RC cars accelerate - unrealistically rapidly from a standstill and then the motor power falls off a cliff and the car cruises at top speed. I'll be designing an electronic controller to shift gears automatically and alter the motors power band so accelerates more like a real car. I purposely read as little information as possible about the Bruiser or P407 before buying this as I find one of the most enjoyable parts of the hobby finding mechanical design flaws and working out how to come up with a solution for them. Some of the problems below are probably common knowledge but new to me and maybe I've attacked them from an angle previously not attempted. So, on with the build! What's this then, it's already built?! Let me explain... This won't be a build in the traditional sense of logging every nut a bolt being put together as per the manual, but instead looking at some of the good and bad points of the kit and re-engineering of the parts that don't work so well. The P407 comes as both an RTR which is simply named "P407" and a kit that requires some assembly named "P407A". The RTR adds a transmitter, receiver, ESC, steering and shifting servos and a lipo battery. The RTR doesn't cost significantly more and seems like good value initially, however, I still went with the P407A for a couple of reasons. Firstly, all the extra gear included in the RTR kit would be surplus to my needs as I already had spare servos and an ESC to use, batteries/radio would be shared with my existing RC cars. I wasn't keen on having all that stuff sit around on my shelf, and probably eventually end up in landfill because I have better parts to use. The second reason becomes more apparent when you receive the kit. The 'kit' arrives partially assembled - most of the oily bits have already been assembled for you. The front and rear axles/diffs, motor/gearbox and most of the ladder frame chassis come as pre-assembled modules so the build consists of the suspension, installing propshafts, steering, wiring the electronics and attaching a few ancillary bits and bobs. The problem is that the pre-assembled modules aren't assembled with the care and attention that most members of this forum would be happy with. You will want to loctite almost every bolt too if you plan on bashing so tearing down was expected. Thankfully they include a full instruction manual for the pre-built modules in addition to a cut-down manual which just assembles the modules together, although the 2012 Bruiser manual will probably get you out of trouble too since this is almost an exact clone. I encountered bolts with the hex heads chewed out due to being over-torqued, bearings with rust on their casings and dust covers missing and bearings that were seized. These parts were tossed out and thankfully I had replacements on hand already. I figure the less parts pre-assembled the better as all the non-assembled parts were in good order. The first modules I tore down were the front and rear axles/diffs. There was a good amount of red grease applied in here, except that not much of it was on the gear teeth haha. I opened up a diff centre and there was ample grease in there too. The internal gears are brass - it was a prick of a job to line up all those gears and get the centre casing back together so I didn't bother disassembling the centre on the other diff - just removed the bolts and loctited them. I noticed that the input shaft of one diff bound up a little bit when I turned it by hand and the problem turned out to be the cast aluminium pinion gear. A bearing fits over the back part of the gear (coloured red below) and since the casting is not perfectly true this caused the pinion and pinion shaft not to run true. The outer part of the gear (coloured blue below) was contacting axle/diff housing. I mounted the gear in my drill press and gently ran a file against both surfaces. I stopped when the bearing started being a loose fit. This helped but it still does not run totally true. Thankfully it no longer binds on the casing and the wobble is mild enough for the universal joint of propshaft to deal with. Ideally you want to mount it in a lathe by the shaft hole and turn it perfectly true. Next I tore down the gearbox. There were several dud bearings installed in here, which were thankfully all common small sizes (5x10x4 mostly IIRC). The gearbox uses steel gears and anodised aluminium hexagonal drives and collars to shift. The motor spur gear and the planetary reduction gears are plastic, although that is not of concern since these gears are subject to the least amount of torque in the entire drivetrain. I believe the Tamiya gearbox has some material removed from the hexagonal parts so they are more 'star' shaped, although functionally they are the same. There was some light oil applied to the shaft and some grease on some of the gears but not nearly enough for my liking. I added more grease to the gears and reassembled. I ran the gearbox just with the motor attached and shifted it by hand and it didn't want to go into some gears easily so I ended up tearing the whole gearbox down again and taking some 400grit sandpaper to the sharp edges of all the hexagonal drives and collars (highlighted red below), cleaned/degreased all the grinding dust and regreased them. After reassembly the gearbox shifted much better, but still was hesitant to go into gears sometimes. Later I found this isn't really a problem - when the output shafts are under load gears shift much easier. Once I had the chassis fully assembled and tried shifting via the servo while in motion, I had a lot of problems with mis-shifting. The culprit turned out to be the servo saver. The included ones are not really strong enough to force the hex collar into the next gear when the hexes aren't synchronised initially. When this happens the gearbox can end up stuck in neutral. Sometimes playing with the throttle is enough to align the gears better so that the weak servo spring can get it into gear, other times you have to resort to hunting around for another gear that works. Since i'm going to have electronics shift for me, mis-shifts must be avoided at all costs. If you get stuck in neutral you'll have no brakes and since the controller could decide to shift at almost any time, randomly having no brakes and needing to intervene to get it back in gear is a deal breaker. I tossed the servo saver and put a straight plastic horn on. Shifting became 100% reliable after doing this. Of course, this will cause the servo to stall out until it can get it into the next gear so shifting must never be attempted when the car is stationary. Fortunately, this is easy enough to implement in the electronic controller. I also tossed the stock servo saver on the steering and put in a plastic one from a TT02 kit, which required the horn to be shortened slightly. Speaking of steering, many will know that this is the achilles heel of the Bruiser. This is due to the arrangement of the white plastic lever shown below which translates the fore and aft movement of the turnbuckle coming from the servo to side-to-side movement that turns the steering knuckle via a second turnbuckle. The problem is that the plastic part can rock side to side because the pivot hole is slightly larger than it needs to be. The side to side movement allows the wheels to turn when there is no fore and aft movement of the servo turnbuckle. There is an aluminium bushing inside the plastic part which was slightly longer than it - I shortened it by 0.5mm or so which allowed the steel part to be tightened down fully onto the white plastic lever. I tightened it just enough until I could feel some resistance when I rotated the plastic lever. This tightened the steering immensely however flex in the plastic part still results in a significant amount of steering slop when trying to turn the wheels against something e.g. when rock crawling. Additionally, the stamped steel part flexes. I plan to make an aluminium lever to replace the plastic one and add an aluminium brace from the head of the bolt to the other side of the chassis to stop flex in the stamped steel part. Next we'll look at the suspension. There is much discussion about removing leaves from the Bruiser suspension to make it less bouncy and have more 'flex' - i'll give my 2cents: no combination of the included leaves works perfectly. With just the main leaf, the rear suspension is a little bit too soft as it sags to about 50% of the travel under the cars own weight. This is probably acceptable for crawling but for the ultimate realism and handling over rough ground at speed, it should sag only about 30-40%, leaving 60-70% of the suspension travel to soak up bumps. At the front, due to the extra weight of the motor and gearbox, just one leaf is way too soft and suspension almost totally compresses under the weight of the car, causing the propshaft and front bash plate to hit the gearbox casing when the car drives over a modest bump. The problem with installing the additional leaves is that they do not increase the stiffness until the ends of the leaves 'engage' (touch) the leaf above them. So for the first ~50% of compression the suspension effectively has 1 leaf and is too soft, then the 2nd and 3rd leafs engage suddenly and the suspension becomes way too stiff. This is the cause of the Bruisers standard suspension configuration being comically bouncy. Even with all 3 leaves, the front suspension still compresses too much under the cars weight. The solution is helper coil springs in the front shock absorber assemblies which will increase stiffness through the entire range of suspension travel. I kept the small leaf as I like the 'scale' look of having multiple leaves, and the small leaf doesn't engage until the suspension is almost bottomed out anyway. Speaking of shocks, the ones included with the P407 are rubbish. Firstly they leaked everywhere. After sorting that out by replacing the o-rings with slightly fatter ones, they had way too much damping even with 350cst oil (thinnest I had), and felt really gritty as the shafts moved so I gave up on them. I purchased a set of Yeah Racing Desert Lizard shocks. These have internal springs and are advertised as 90mm but are actually longer than this (~100mm) because they have a 'droop spring' installed on the other side of the piston which prevents the shock drooping all the way. I'm going to leave this spring out - the leaf springs will limit droop anyway. There is a good selection of springs included so I should be able to find a combination which stiffen the front and rear suspension appropriately. The threaded end of the shaft is too short to fit the Bruisers rubber strut top but this is solved by installing 1 nut and then a brass standoff which the rubber bushing fits over, and then installing the second nut onto the thread of the standoff. Since the shock body is longer than standard, the standard shock mount on the axle won't work. I quickly cut an aluminium adaptor bracket and bolt spacer/sleeve to see if it would work. Turns out I don't have long enough bolts on hand, so I put some brass stand offs just to mock things up. Seems to be workable! Now I just need to get the correct length bolts, make enough for all 4 wheels and make them look presentable (round over the corners!) The next problem was that the rear trailing arms made jingling noises as the car drove over bumps. This was fixed by adding a 2nd rubber o-ring to the bottom side where it is attached to the chassis, and adding some adhesive backed closed cell foam around the axle end. A final simple and effective mod is to raise the front of the gearbox. I put 4mm of aluminium spacers at each mount. This gives more clearance for the front suspension to compress and tilts the gearbox at an angle, allowing the front axle to be tilted back at the same angle without causing vibrations of the propshaft due to different universal joint angles. Angling the axle backwards introduces caster to the front wheels which will make it more stable at speed. The angle of the rear axle should be adjusted too - there is no handling effect from changing it, it'll just allow the propshaft to run vibration-free again. Train spotters will notice the red motor. This is a trackstar 13.5t brushless instead of the included 540 brushed motor. There was nothing wrong with the included motor however the brushless is needed for the automatic shifting electronics I intend to build. It probably seems strange that I chose a 13.5t motor when even a 25t is probably overpowered for 'scale' driving. The reason for the motor choice is that I need the 3000kv to reach a realistic top speed without altering the standard gearing and the excessive power of the motor can always be dialled back by electronic control. In fact, having an excess of torque is desirable as torque-limiting can be used to shape the torque curve of the motor in a way that mimics an internal combustion engine and make it accelerate more realistically. We can take away torque at a given rpm but we can't add more, so starting with a powerful motor is more flexible. Also if I get bored with 'scale' driving can just turn torque limiting off and do mad launches Brushless allows motor speed sensing to be implemented with minimal complexity - I went with sensored since it further simplifies the speed-sensing electronics and the motor will run smoother when crawling. Also the spare ESC I had required a sensored motor. As far as the automatic gearbox controller goes I've got an Arduino reading 4 channels from the receiver and outputting 2 channels continuously. Still need to implement reading the motor rpm but that should be straight forward. The controller will sit between the receiver and the ESC / gearbox servo. It'll also tap off the motor sensor cable. By monitoring the motor rpm the controller will decide when it needs to shift gears and can intercept the throttle signal to either blip or cut the throttle to ensure a smooth gear change. Since I'm already intercepting the throttle signal and measuring motor rpm, implementing motor torque limiting/shaping is just a matter of software. Realistically the motor power should be turned down such that the acceleration is the same as the real car - if the 1:1 car does 0-100kmh in 12 seconds, then rc should do 0-11kmh in the same amount of time since the scale is roughly 1:9. With the correct amount of power and a realistic torque curve it should actually accelerate faster to it's top speed by working through the gears instead of just putting it in 3rd gear and planting it from a standstill. Another feature that should probably be implemented is to limit the braking force in 1st and 2nd gear so it matches 3rd gear, due to the braking force being multiplied by the gear ratios. I'll post more when there is something interesting to show! I think that's it for now
  2. 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!
  3. First untethered drive. Needs tweaking to smooth out the shifts, though half of the problem is probably the untamed fury of the 13.5t
  4. 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.
  5. 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!
  6. 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.
  7. 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.
  8. 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
  9. 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?
  10. 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.
  11. 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.
  12. 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.
  13. 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.
  14. nbTMM

    So, What Have You Done Today?

    Made some double cardan driveshafts for a TT02 by fitting Yeah Racing adjustable dogbone ends (from some 'drift' universal shafts) to 3racing SAK-X27 shafts. Changing the 4mm inner wheel bearings to 3mm was needed line up the pinhole. Serrated wheel nuts were needed since the threaded section of the shaft is too short for a nyloc nut. Runs heaps smoother than CV/dogbone shafts or universals. Top: CV/dogbone shaft Middle: Universal shaft Bottom: Double cardan shaft
  15. nbTMM

    Cad design for fibre lyte

    Depends how tight of a fit you want and how well made the screws are. I think ideally M3 screws are maximum of 3.0mm but they are always smaller because the threads are a bit rounded over. If the material that the hole is in is hard (e.g. stainless steel), you will want to make your hole at least 3.0mm to ensure that the threads don't bind up in the hole due to slight misalignment. If i want an M3 screw to self tap into soft plastic, use a 2.5mm hole. If a bit of slop is no problem you might even make your holes 3.2mm for ease of assembly, especially if you've got a lot of holes to line up. If you want an optimum fit then you can always start off with the holes small and re-drill them larger as necessary during assembly.
  16. nbTMM

    Cad design for fibre lyte

    They will import your file into their software and do the necessary editing to ensure that it is cut as intended with their machine. Usually they will want a dimension to confirm the scale of the drawing so there isn't some misunderstanding and you get parts that are overall bigger/smaller than expected. It can also clarify if the finished dimension of the part is inside, outside or down the centre of the lines if the lines are drawn with non-negligible thickness. Labelling the finished sizes of some holes (e.g. 'ΓΈ3mm') will also help communicate how you've drawn things.
  17. What has changed in the last 10 or 15 years is that social media and streaming video has enabled instant gratification. Thinking is mentally taxing and doing stuff is physically taxing. Posting a picture of cat or a stupid meme and getting 'likes' gives instant gratification with minimal effort. Giving and receiving 'likes' reinforces the feeling of belonging to a group and/or being socially accepted. Watching someone skilled accomplish something lessens the need for us to learn that skill for ourselves - by simply watching them succeed, we too get the gratification of succeeding. I mean, people even watch videos of other people playing video games because it gives them the gratification of playing a game without the effort of actually playing it... Even on this forum we are guilty of it - looking at build logs and photos of others working on RCs, giving and receiving 'likes', gives us our 'hit' and lessens the need for us to do significant work on our own stuff, or actually get out and drive our RCs with like minded people to be content.
  18. nbTMM

    So, What Have You Done Today?

    Trialling these 76x32mm ebay tyres on the TT02 rally build. Lookin' phat on 24mm wheels.
  19. nbTMM

    tble02s esc

    Is the battery fully charged? Have you followed the "high point setup" procedure in the manual (https://www.trap.co.za/tamiya tble 02s.pdf) ? Also check the throttle direction is not reversed on your transmitter.
  20. nbTMM

    measuring flexibility/stiffness

    I can see how a bike would benefit from a flexible chassis because when the bike is tilted the motion ratio of the suspension has changed and the suspension is significantly stiffer. Allowing the chassis to flex in the horizontal direction only lowers the effective spring rate when leaning without affecting the suspension operation when the bike is upright. In an off road RC car I can't see this being the case nearly as much because flexible chassis such as those cut from CFRP/GFRP sheet are mostly flexible in the vertical axis and almost ideally stiff in both horizontal axes. The chassis only wants to flex significantly in almost exactly the same axis as the suspension hinges, so it doesn't really change much in the case of the wheel being compressed at an extreme angle such as landing off a jump crooked. The only significant difference is that the chassis will flex across it's entire length/width, effectively acting as a really long suspension arm so it will give more effective camber gain versus the suspension arm pivoting with a softer spring/damper. Dial in more camber gain and a softer spring/damper with a rigid chassis and you achieve a similar spring rate and geometry as the flexible chassis however it is now a properly damped system.
  21. nbTMM

    measuring flexibility/stiffness

    My train of thought is that flex in the chassis acts as part of the suspension however it is an undamped spring which is not good for car control. A rigid chassis allows the wheel movement to be fully controlled by the intended suspension which can be properly damped. If the car seems to drive better with a flexible chassis compared to a rigid chassis then either the suspension spring rate and/or damper rate is too high, or the geometry of the suspension (particularly camber gain) needs tweaking. Lower spring and damper rates, and more camber gain should make a rigid chassis feel more like a flexible chassis however with more control (less bouncy) Same goes for flexible suspension arms, links, strut towers etc - they add undamped springs to the suspension.
  22. If there is a gap then it'll leak and there is always a gap. 1M cst will still leak through a hairline crack, just 1000 times slower than 1K cst, which may make the leak rate acceptable in a poorly sealed diff. Having O-rings and gaskets just reduces the leak rate substantially so thin oils can be used with an acceptable leak rate. There's no such thing as perfectly sealed, especially when outdrives have to rotate inside an o-ring, and hydraulic pressure can force the oil past a flexible seal.
  23. nbTMM

    Slash 4x4 heat on 3s.

    Both esc and motor both have resistive losses which increase with the square of electrical current (if current doubles, heat quadruples). In the motor, the resistance of the windings, in the esc the resistance of the MOSFET transistors. Current is highest at stall, so the slower the motor is turning the hotter BOTH motor and esc get. When you increase the FDR (smaller pinion), the motor rpms increase for the same road speed and acceleration increases so you spend more time at high motor rpms where the current is low, therefore both motor and esc run cooler. Additionally, the esc has switching losses, which occur due to the transistor resistance being at an intermediate value between on and off resistances. Technically if operating at higher RPMs, more switching is occurring therefore there are greater switching losses in the ESC and it heats up a bit more, although I suspect this effect is negligible compared to the current as long as the ESC is designed properly and doesn't spend too much time with the transistors 'half on'.
  24. nbTMM

    Slash 4x4 heat on 3s.

    A low kv motor will have less torque than a high kv motor on the same battery. A lower kv motor will be slower in every way. The only advantages of a lower kv motor is that it runs cooler and doesn't drain the battery as fast, and well... it is slower which is advantageous if you want to crawl or run an entry level racing class. As far as high kv low voltage vs low kv higher voltage, it doesn't make too much difference as long as kv*volts is the same. More important is the overall power output and gearing. Motors have horrible efficiency down low in their rpm range so if you have the car geared for 100kmh unloaded wheel speed, but spend most of the time full throttle at 20kmh the efficiency will be terrible, probably less than 20%. That means that 80% of the power coming from the battery just gets turned in to heat. If you change your gearing so the unloaded wheel speed is only 50kmh then it'll ran way cooler when you're driving at 20kmh due to operating the motor at much higher efficiency, perhaps 60% - now only 40% of power is turned into heat and everything runs much cooler. The sacrifice is in top speed. A high power setup (higher kv, lower turns, more cells battery) will run hotter than a low power setup, so it makes sense to try to operate it at higher efficiency to manage heat. That is why with a high kv / low turns motor, it is usually recommended to run a higher FDR than a low kv / high turns motor. If you want to run a high power setup with a low FDR, either you need to increase the amount of cooling (use a physically larger motor e.g. 550 size motor instead of 540, ESC with lower resistance MOSFETs and/or larger heatsink/fan), or just accept that it's not going to be able to run for very long before it overheats. Melted as in warped, or just discoloured? If the former, it sounds like something has gone horribly wrong. Plastic doesn't melt until >120*C, and I would think the velineon esc should go into an overheat protection mode before it gets to that. Perhaps your motor and/or ESC have been damaged.
  25. Ignore them. They are just looking for a reaction. If you give them nothing they will get bored and find something/someone else to amuse themselves. They are probably killing time in the street because their druggy parents haven't provided them enough resources to amuse themselves at home.