Cross-posting this from Tamiyaclub forums, figured that there would be interest here as well 
. There's a few posts to edit and repost here. will throw them up here to get everyone up to speed.
Teaser:
The main reason (other than the price) that I went for the P407 over a real bruiser 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.
. There's a few posts to edit and repost here. will throw them up here to get everyone up to speed.Teaser:
The main reason (other than the price) that I went for the P407 over a real bruiser 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.
)
. I made it work though :mrgreen:
