Samix V2 chassis conversion for the TRF418

I have to confess that I’ve been struggling with the Tamiya TRF418. Although there are a great many things to like about this car, the handling on carpet (for me at least) has not been one of them. I’ve tried all the tricks that have worked with other cars in the past and none of them have made a enough of a difference – the rear of the car has always been extremely edgy and unpredictable.

A radical change was required.

I pondered a complete change of car – the TRF419 is tempting, but after my poor experience with the TRF418 it may well prove to be another failure. The latest Yokomo won the worlds and seems to have the most refined design of any of the traditional 2-belt cars. I could go on. But my decision was made when I noticed that Samix had released an updated version of their chassis conversion. “Buy it now”.

The Samix V2 carbon fibre conversion

Before I go any further let me mention the excellent review of this chassis on kentech’s blog. My conclusions are pretty similar, and my pictures are not as good. But there are a couple of small differences in the V2 chassis that I thought it would be worth sharing.

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In the package (just a plastic bag with a header card, the style of the packaging suggests it is made in a Chinese factory somewhere) you get the bits and bobs pictured above. The full conversion includes both a lower and upper deck, a centre-line motor bulkhead, a front steering bridge and some LiPo mounting jaws. You can buy just the chassis plate if you want, and there is also an aluminium chassis option if you like your car to be too heavy and too stiff…

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If we take a look at the chassis, compared to the original Tamiya plate (on the left) you can see that it is not as waisted between the suspension mounts and the central area, and has slightly different cut-outs (mainly to accommodate the new motor mount). The chassis is drilled for the original Tamiya motor mount too. At the front, you can see that Samix have included an alternative set of steering post mounting holes, further forward than kit. These will give quite extreme Ackermann and I’m not entirely sure when you would want to use them. There are also holes for the battery mounts and the optional fan mount. The Samix chassis is a couple of mm narrower overall, and pretty much the same thickness at ~2.3mm.

The biggest difference is the amount of flex. The Samix chassis is significantly softer than the Tamiya one.

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The top decks are very similar. Same thickness (~2mm) and similar amounts of flex – the main difference being the extra hole at the front of the Samix deck to fit the steering bridge if using the alternative Ackermann setting.

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The other big change with the Samix conversion is the centreline motor bulkhead. This is another step closer to equal left and right flex. Samix have chosen to use a floating layshaft and supply some different flanged bearings to allow it to work with the Tamiya pulleys. The final assembly is pretty solid – just take care that you build it with the right screws in the right places as there are no instructions! The motor is now only held in with two screws at the bottom. I’m not a fan of this design but a lot of cars have been using it recently and I don’t recall seeing any damage because of it. A feature that I do like is the way that the bulkhead post is completely removable – so if you choose to run without the top centre screw, you can remove the part that touches the top deck as well. I’m running mine with the screw to start with.

The quality of these parts is pretty good and although the anodising is not 100% consistent, the colour is very close to Tamiya’s own and you don’t notice anything when they are in the car. For some reason my spur and pulleys would only spin freely when fitted in a particular direction, so keep an eye out for that.

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Staying on the topic of quality, there was only one part that needed a little extra work, and that was the top deck. The leading edge is just a fraction of a mm too long and binds against the bulkheads. A few minutes with an emery board solved this – you want the top deck to drop easily into place to prevent tweak. There is no problem at all with the position of the drilled holes – the chassis builds up as straight as the original. This was something that kentech noticed in his build, so obviously there hasn’t been a change to the top deck dimensions in the V2 kit.

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I also treated myself to Samix’s 40mm fan mount. This is nicely made from aluminium, and as you can see it has a small channel at the side to guide the fan wire. They also offer a 30mm mount. Naturally the chassis comes pre-drilled for this accessory and it fits neatly just behind the motor. I use a 40mm x 15mm fan and I have to say that it is held in place very solidly by a couple of M3x20mm screws – much stronger than servo tape.

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Once completed, the Samix TRF418 looks something like this. It takes a little time to swap over the parts, but as I mentioned before the quality is good and everything fits in place.

I’ll briefly mention the LiPo mounts – the jaws are a good size for the standard race LiPo’s, and have a small range of adjustment. More importantly, the tape slots are in a slightly different place and grip the LiPo a lot better. It’s a small change but one that really gives you a lot more confidence in the battery mounting. I won’t shed a tear for the misaligned servo mounts that Tamiya expected me to use in the original kit!

The final thing I want to mention about the build is the flex (again). Once the bulkheads are bolted on, the extra flex of the lower deck is somewhat reduced. However you can still feel the difference in your hands.

The first race

Of course a car that looks good on the bench is one thing but what really matters is how it goes on the track.

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My debut with the Samix TRF418 was at the second meeting of the CWIC series earlier today. This is a popular carpet series on a 30x20m track with a competitive field of over 50 entries in 17.5 Blinky. The first meeting with the standard TRF418 was a real struggle, I just couldn’t get any consistency out of the car and ended up well off the pace.

The performance of the Samix TRF418 seems to be a solid step forward.

If I could characterise the original 418, it was a car that started the day undriveable, and ended the day tricky. The Samix started the day tricky, and ended the day driveable. I’m OK with that – the track is always low on grip in the first round, and I would rather have a car that is lively when the grip is low than one that understeers when the grip is high. The balance of the Samix throughout the rest of the day was good – neutral, with a nice flow through the corners. It would slide the rear end a little if you were aggressive with the throttle or steering, but this can help get the car into the corners. The original 418 was so inconsistent that you could never tell which direction the rear end would go next!

The car was reliable all day too – nothing came loose, nothing broke. You might notice from the picture above that the ESC is now a Hobbywing Xtreme Stock – this is because I clumsily damaged my LRP Flow while trying to re-attach the switch the the circuit board. Lead-free factory solder is not an easy thing to remove!

Although I qualified in more or less the same place I qualified last time, I was much closer to the A-final on pace and could have got into it without a couple of mistakes in the last round of qualifying. The added predictability of the Samix conversion made it a much easier car to race with and I left with a 1st and 3rd in the B-final. And a smile on my face as well 🙂

Dave

PS I am also racing Mini in the CWIC this year. There is a very tight battle at the head of the grid. My Tamiya M-05 is very well sorted now, and the setup has barely changed for the last couple of years. So far I’m leading the championship but every point matters because there is nothing in it between the top three. Good fun.

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