nbTMM

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Posts posted by nbTMM


  1. 15 hours ago, markbt73 said:

    Good grief - what are you doing to that poor car that's breaking stainless bolts? In a 1:1 car, I agree; don't use them for anything structural or drivetrain-related. But for our little RC cars, I just can't see it being a problem. The loads aren't that big. I've never even broken an aluminum screw, let alone a stainless one. Bent, stripped, rounded heads, sure, but never broken.

    When the car does it's best cartwheel impression at 80kmh :). They usually bend a little before they snap. And yes, the heads getting ground off where there is a ground clearance issue - that's a problem for any type of screw though.


  2. So, the body. The body was sprayed with TS-38 Gun metal. The idea is that it is close enough to the black plastic that if it scrapes through it won't be overly noticeable. This was my first time painting a hard body so I made plenty of rookie mistakes. Minors runs, dust and dirt, that kind of thing. Also made the mistake of spraying the cab and tray separately from different angles so the metallic flake doesn't match up where they meet. No matter, the aim here is that if it looks cool from a metre away, mission accomplished. I think the bruiser's 'sleeper cab' looks ugly as sin so I built the body as a single cab ute instead. Of course, there is no back window supplied with the body so I laser cut one at work out of two pieces of 1.5mm acrylic. The interior was painted in TS-46 Light Sand, with some matte black and silver brushwork for the floor, dashboard and steering wheel. The dash decals were pre-applied to the interior tub and not easily removable, so I just painted around them.

    ss66iZL.png

    QaQ57Gy.png

    ogGluU4.png

    Aluminium tape inside these light buckets improves their realism
    y2naTXF.png3aSqI3Y.png

    PFTyLTN.png

    Some choice decals from the sticker sheet were applied, I might get a white tailgate logo as I didn't think the included red logo would go well with the gun metal.

    IkLXPr5.png

    ZqnahTQ.png
     

    YVP67A5.png

    ZLd4ziQ.png

     

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  3. Stainless bolts are weak - don't use them anywhere they need to take a big load, especially a shear load, because they will snap. Get 10.9 or 12.9 alloy steel bolts ('grade 8' for imperial folk). They will rust if they get wet, but they won't break. I've filled my spare parts bins with most lengths of M3 button head hex 12.9 bolts, the cheapest from ebay, and never had an issue.

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  4. This week it was time to replace the toy-like bumpers and side sliders/steps

    i got these generic steel side steps from ebay. The main square section extended past the step part and had mounting holes at either end. I cut these off and drilled two new holes underneath the step so I could utilise existing chassis bolt locations for mounting.

    pRvKukw.png

    p4MuNnc.png

    Up front, I made an aluminium part which ties together the 6 bolts that the standard bruiser bar mounts to
    T0k2E5Y.png

    This allows a steel front bar to mount securely, and the chassis probably won't get bent if I accidentally bulldoze a small country. The front bar is the same as an RC4WD Trail Finder bar, but it's a cheap knockoff / factory second or some such that I found on ebay. The quality is not A1, some bars are off by a mm to two, but it's good enough for my purposes. I had to bend the steel plate section of the front bar a little as the bruiser chassis has a downward slope towards the front - I guess if I have a hard crash this is the part that is going to bend. There's a spot for mounting a winch on the plate section of the bar - I decided to put an LED light bar there instead.

    jkvUfMM.png

    kr3cBCO.png

    Down rear is another knockoff RC4WD bar. It turns out the bruiser body is about 1cm wider than the trailfinder body around the rear tail lights so the bar wouldn't fit. Fortunately, I was able to tilt over each corner/taillight section with the persuasion of a hammer so the top bar sits out 5mm wider than the bottom bar - as supplied top and bottom bars were equal width. I was worried the welds (or brazes?) would crack when I tried to do this, but they held up. Some paint cracked at the joints, but I just gave it a touch up with a brush and you'd never notice if I didn't point it out ;). The bottom bar sits underneath the body so it doesn't need to be wider. Another aluminium mounting solution mates it to the bruiser chassis.
    UlV4OJL.png

    More black paint keeps things stealthy and factory looking
    dLDqWOA.png

    Ready for a body - that's the next post!
    qixn0my.png


  5. The metal balls upgrade should help a lot. The TT02RR upper arms are fairly fragile. If (when) they break, you can just screw a ball into the top of the upright, then get some aftermarket adjustable aluminium arms and put a regular ball joint end onto the turnbuckle instead of the huge TT02 style ball end. This works because the upper ball joint doesn't take the weight of the car so the upper ball needn't have such high retaining force. The bottom ball joint does, because that is where the shock is attached so you have to retain the big ball joint.

    ejrCWgg.jpg

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  6. even if the bevel gears in the diff were totally locked up, it wouldn't cause any drivetrain loss when driving straight because those gears only rotate when one wheel is spinning faster than the other. Try removing the propshaft and turning the front prop joint by hand. If it spins easily then the front diff isn't the cause of the sluggishness in a straight line. If it is hard to turn then at least you know the problem is something in the front gearbox.


  7. I was tempted to do that initially but thought I'd see if the standard configuration could be made to work properly. The standard setup also has an advantage that the turnbuckle going to the steering knuckle is longer and less angled than when you do the front servo mod, which gives less bump steer. Ideally the servo should be mounted exactly where the standard lever pivot is, and that just isn't possible.


  8. The rear shocks were mounted exactly the same way as the fronts were. I had to cut away parts of the rear swing arms for the aluminium spacer to fit - this isn't an issue as the swing arms are just for show and don't bear any suspension loads. I could have reversed the mounts so the shocks were to the rear of the axle instead of the front as there are additional holes in the chassis to do this, however I think it looks better this way as my shock mount is tucked away and better hidden. I'm glad I didn't attempt to narrow the rear axle any further - the shocks are close to the tyres. If one rear wheel is fully drooped and the other is fully compressed the shock body does gently rub the tyre but not enough to be a problem.
    IK10mEK.jpg


    For springs I used the same configuration as the front with just the main leaf and the softest spring inside the shocks. This was a little too stiff since there is less weight over the rear axle than the front. The roll stiffness is higher at the rear because the springs and shocks are mounted further outwards from the centre of the car than on the front axle. This made a rear wheel lift off the ground first when flexing over uneven ground. Making the rear springs slightly softer than the front would match the roll stiffness between front and rear and give the most flex. Removing the internal shock spring made it too soft, so I kept the soft shock spring but moved the mounting position of the leaf shackle on the chassis. By moving the mounting point forward the shackle lays down slightly which results in a softer spring rate from the leaf. I also moved the shackle mount down slightly to regain some ride height. When the suspension is bottomed out the shackle is almost horizontal so this is as far forward as the shackle can be mounted without it trying to over-centre. The red circles show the original mounting holes on the chassis.

    8NKlorF.png

    I made an aluminium steering lever to replace the plastic one which flexed a lot. Also fashioned up an aluminium brace which ties the bottom of the lever pivot to the other side of the chassis. The steering is far stronger now. The weak point now actually seems to be the plastic rails that the servos are mounted on - it flexes under steering loads.

    fVx0xZ4.png


    The front bash plate also got a trim so the front suspension can now compress fully without the edge of the plate hitting the gearbox

    MTFmiVW.png

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  9. That circuit board is just an Arduino Pro Mini development board that they have loaded their custom 4WS software on - the holes are 0.1" / 2.54mm apart so not too difficult to solder. Shouldn't need a special tip on your soldering iron but having a vice or 'helping hands' to hold the circuit board and wires still while you solder will be invaluable. It looks like they get you to cut the two 3-pin cables in half, strip and solder the bare ends to the Arduino board. The hardest part will be stripping the 3 wire ends to the correct lengths without breaking off too many strands of copper which will cause the wire end to be weak. The insulation on those 3-pin cables usually is PVC instead of silicone like is used for RC power cables, so you have to work quickly with the solder iron to prevent melting the PVC insulation too much. Some glue (epoxy glue, hot glue) for strain relief is usually a good idea where you terminate bare wire to circuit boards too.


  10. Different model servos can rotate different directions. The choice of clockwise or anti-clockwise operation by the servo manufacturer seems completely arbitrary. If you have a few servos lying around you might be able to find two different servos that rotate opposite directions, then you can just use them with a Y cable. Reversing the external wiring of the servo will just cause it to stop working. It is possible to reverse the wiring of the internal potentiometer and motor which has the effect of reversing the direction of the servo:

     

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  11. Just now, graemevw said:

    If i had an adjustable psu id use it. I havent though so im hoping by using an alarm too, i can get it to cut before the alarm reaches what ive set it to. (Esc should cut at 6.3v, alarm is set to 6.2v)

    Sounds like a logical solution to me B)


  12. 1 hour ago, Juls1 said:

    The stock esc is set to 3v per cell, so 6v cut off.

    Actually the TBLE02S is configured to 2.45V/cell = 4.9V cutoff, way too low for regular LiPo chemistries but OK for NiMH and LiFePO4 which Tamiya recommend. Both the link in the previous post and my own testing confirm that it is 4.9V.

    The correct way to test the cutoff voltage after doing the resistor mod is to power the ESC with a variable DC powersupply instead of a battery. Hold the throttle down (doesn't have to be full throttle, just constantly running the motor), and slowly lower the voltage on the powersupply. When you reach the cutoff voltage the motor will stop running.

    You could also run down an NiMH battery until cutoff kicks in, but be aware that a NiMH battery's voltage will sag significantly under load, causing cutoff to trip, and then the battery will quickly recover in voltage possibly 1 volt or more. So you have to be measuring the voltage with a multimeter at the exact moment that the cutoff circuit trips. If you can run down the battery enough that you can get the cutoff to kick in while holding the car in the air and only being partly on the throttle, I'd recommend measuring the battery voltage under that condition.


  13. 1 hour ago, salvine said:

    Important to note that "0 offset' RC touring car wheels are not actually 0 offset in the traditional sense. The surface on the wheel that mates to the hex adapter on a +0 wheel is actually about 6mm from the wheel centerline. I assume this is because the offset is measured with a hex adapter installed (6mm hex thickness perhaps?).


  14. If you replace +0 wheels with +6 wheels of the same width then the car becomes 12mm wider overall (6mm each side) measured from inner tyre edge to inner tyre edge, or outer tyre edge to outer tyre edge. Replacing the wheel hexes with different thickness ones has the same effect e.g. replacing a 6mm thick hex with a 12mm thick hex is the same effect as going from a +0 wheel to a +6 wheel. You'll need longer axles if you want to increase the hex thickness that much though.

    If you replace 24mm wide wheels with 30mm wide wheels, same wheel offset, then it becomes 6mm wider overall (3mm each side) measured from the outer edge to outer edge and 6mm narrower overall (3mm per side) measured from inner edge to inner edge.

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  15. These ones?
    https://www.fastrax-rc.com/index.php?_route_=fastrax-tamiya-tt02-aluminium-rear-hub-carriers-2&search=tt02&page=2

    Looks like they are just the Jazrider ones:
    https://www.jazrider.com/tamiya-tt02-aluminum-rear-hub-carrier-light-blue-p-90061693.html

    I actually have a set of those, and mine fit fine... until I stopped using them - get hubs with 2-3deg toe, much better than these which have no toe. If they are too tight, just gently hand file/sand the hub or arm until it fits. You actually want a tight fit on these because slop in the pivot will make the wheel flop around and lead to unstable handling. More often than not I find myself actually throwing 3mm shims in that joint to tighten it up, especially after parts have worn.

     


  16. The chart below shows you the possible gear ratios (aka final drive ratio or FDR) using the standard plastic motor mount and either the 68T (high speed), 64T (option) or 70T (standard) spur gears. You don't need the high speed gear set nor an aluminium mount to use a 22T pinion. It will fit with the standard 70T pinion gear just by moving the motor to a different set of holes in the plastic motor mount, see the chart below. 

    The lower your final drive ratio, the less acceleration/torque you'll have but the higher your potential top speed will be. If you change to a 22T pinion from a 17T the car will certainly reach a higher top speed on smooth asphalt but it may go even slower on grass or gravel because it may no longer have enough torque low down to power through the rough ground. My advice would be to buy a 22T 0.6mod pinion since they are cheap, install it and see the effect for yourself. 

    The main advantage of the high speed hopup is not to change the 70T spur gear for a 68T, since that is an almost unnoticeable change. The purpose is that you get the aluminium gear mount in the set so you need not restrict yourself to tamiya spur gears anymore. Any gear with 4 mounting holes that line up with the aluminium gear mount can now be used. Common aftermarket gears have a tooth pitch of 48P or 64P. 48P is a finer imperial tooth pitch than the metric '0.6mod' pitch that Tamiya normally use. 64P is an even finer tooth pitch again. As a rule of thumb, the finer the teeth the quieter and smoother the gears run but the more fragile they are. If you buy high quality 64P gears they will still be stronger and last longer than low quality 48P or 0.6mod gears however.

    When you start using 48P or 64P pitch gears instead of 0.6mod then you also need the Yeah Racing mount because the holes in the Tamiya mounts only give you adjustments which mesh 0.6mod gears properly. The Yeah Racing mount allows one motor screw to slide in a slot so that it is infinitely adjustable. That can be advantageous when you want to achieve a much lower final drive ratio than possible using 64T-70T spurs. Brushless motors typically have much higher torque than brushed and lower maximum rpm so they require a lower final drive ratio. Similarly, touring cars which race on smooth tracks will favour a lower final drive ratio since torque will be traded for higher top speed down the straights. It would not be unheard of for instance to run a final drive ratio of around 3.50 1 on a TT02 touring car with a 21.5turn brushless motor.

    There is honestly not much difference between the different tamiya 23-27turn brushed motors (silver can, sport tuned, torque tuned, super stock, etc). If you're after a significant jump in speed and power you'd be far better off going straight to a brushless motor and playing with gear ratios later. 13.5turn sensored brushless motor would be a good starting point and will work with the TBLE02S ESC if that's what you've got at the moment.

    Chart_zpsrtd4lzwn.jpg

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  17. 20Amps is the current rating. About 60-80A would be considered average for an 1/10 scale ESC these days. The higher the current, the more torque/power your motor will make when it is at stall (not turning, or turning very slowly) such as when climbing a rock or steep hill very slowly. Many ESCs like the Tamiya TBLE02S will go into a torque limiting mode when the maximum current is reached (such as when the motor can't turn the wheels because they are jammed by an obstacle), at which point you hear a buzzing or hammering sound coming from the motor, this is to protect the ESC from overload. Cheaper ESCs will simply just try to put out maximum current at all times and if pushed too far, blow up.  If you get a beefy ESC you have to be mindful that the motor can't take a huge stall current indefinitely. Too much stall current for too long will make your motor overheat and fail.

    Looks like you're paying a premium for the Servonaut one for the integration with the Servonaut light and sound modules. They also make a claim about having more steps of speed control, which would give you finer throttle control, especially at low throttle which might be important for crawling. Without actually checking, I would hazard a guess that most half decent (>$80) escs would have fine enough throttle control for crawling anyway. The servonaut also switches at 16kHz so won't make an annoying squealing sound when at partial throttle. Other than those points, the servonaut one doesn't look like anything special to me, seems quite expensive for what it is.


  18. Less pinion teeth = more acceleration/torque, lower top speed

    More pinion teeth = less acceleration/torque, higher top speed 

    The difference between 18t and 20t will be barely noticeable. For crawling you want lots of torque and a manageable speed so use as few pinion teeth as possible. For speedruns/bashing you probably want more teeth. 


  19. the telemetry capable receivers (e.g. GT5) cannot because they rebind the TX. I can't bind two GT5 RXs to the same model memory in my GT5 TX. I can however bind one GT5 RX to one model memory slot and another GT5 RX to another model memory slot. It's probably unlikely that you'd actually want to use two RXs simultaneously unless you want to double up on RX outputs in the same model, or drive two cars simultaneously using one TX.

    On my old GT2 TX I could bind as many GT2 RXs as I wanted to it and they'd all work simultaneously. I assume GT3 TX/RX work the same as GT2.
     


  20. The rear axle required a bit more work. RC4WD supplies replacement rear axles for their hex conversion kit, which have 4mm threaded ends and a drive pin hole. They are otherwise exactly the same as standard - or they would be if you had a real Bruiser. The real bruiser has splined ends where the axle goes into the diff. On the HG P407, the axles have flats instead as this is probably cheaper to make.
    ZzsPaLQ.png

    Fortunately the outer diameter of the splined section is the same as the rest of the shaft, so I could file some flats in the splined section to make them compatible with the P407. The presence of the splines instead of a smooth shaft seemingly has no impact on functionality.

    eeDvamV.png

    With that solved, the rear axle can be reassembled with the new shafts, drive pins, rc4wd hex adaptors and wheels, much the same as for the front axle. The fit was too tight and the bearings bound up exactly the same as the front, but I'll fix that later as the primary concern right now is to correct this:
    r4QPcO3.jpg

    2ykXa4S.png

    As seen above, the track of the rear axle is about 15-16mm wider than the front. This isn't too noticeable with the bruisers monster truck wheels but looks weird with skinnier wheels and tyres. I've seen other people narrow the rear axle in various ways usually involving removing the large outer wheel bearing and cutting the cast axle casing with a hacksaw. I didn't want to do that. First, it's a non reversible mod. Secondly, removing one of the wheel bearings isn't a good idea, especially on a car as heavy as the bruiser as it transfers the wheel load via the axle to the bearing near the diff, and the axle will inevitably bend a little when this happens which causes friction and things wearing out faster than they should. I saw the opportunity for a less destructive narrowing mod in the standard bearing arrangement. The standard setup uses a 10x5x4mm inner wheel bearing and a machined aluminium sleeve which the 16x8x5 outer wheel bearing is located by. If you remove the aluminium sleeve, a second 10x5x4 bearing will fit inside the axle casing. It's smaller than the standard bearing but is much better than no bearing.
    d2PemeU.png

    5r9tWXL.png

    This allows the hex adaptor to sit about 5-6mm further inward as the width of the 16x8x5 outer bearing has been eliminated. It also converts the outer bearing back to a conventional configuration where the inner race rotates with the axle and the outer race is stationary, which in turn removes the requirement to use the special hex adaptor. A thinner 12mm hex adapter can be used. As can be seen above, the pin hole in the axle needs to be moved in about 5.5mm to suit the new setup. Much cursing at blunt drill bits later was have this:
    12VWXV6.png

    bHOLug9.png

    The only thing left to do is shim the axles so they don't have end play nor bind the bearings when the wheel nut is tightened. This can be done in 4 places (below) between the e-clips and bearings to either shift the axle inwards (tighter) or outwards (looser). There was about 2mm of space to take up at the two outer locations since I removed the standard machined aluminium sleeve parts and the bearings need to be pressed outwards as the e-clip riding against them prevents the axle being pulled out, while the e-clip riding on the bearings near the diff prevent the axles being pushed in. After taking this pic I actually replaced each of the 10x5x4mm bearings in question with two 10x5x3mm bearings, therefore only a couple of shims were required instead of like 20 shims.
    vuRRSsV.png

    The next obstacle was that some of the unthreaded 5mm shaft was now poking through the hex, and the wheel hubs only have 4mm holes.
    2J35AQS.png

    I drilled the wheel hubs to 5mm. Now the wheels fit all the way on, but some unthreaded shaft still pokes out the front of the wheel, so the wheel nut won't go all the way on. I threw some 5mm washers on as a dodgy fix just so the wheel nut would tighten down. I'll probably grind that part down and cut the threads further on to the shaft with a die. The axles need to be cut shorter as all that thread sticking out looks silly.

    mPQoNT0.png

    The blue hexes can barely be seen once the wheels are mounted 

    seuVVKc.png

    And most importantly the rear track has been reduced almost to that of the front axle. There's still a couple mm difference although I don't think it'll be noticeable. I could always space out the front wheels slightly (although that increases scrub radius which is unrealistic), or find/machine thinner hexes for the rear.

    3Uo9uIh.jpg

    That's all for now!

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