h2e

So the MSX is more and more becoming a close brother to the TRF420X, with the motor central and the drive belt inverted. Now, the belt routing is in a way that it reduces off-power instability and on-power steering. Both traits of a car that I am longing for.

To do so, I flipped bat and electrics, motor mount and servo mount. The drive train is almost like my h2e five now, just with more spacing between motor and battery.

TA07MSX w/ inverted drive belt. Only changes: 2 new topdeck parts. Rest of the chassis is symmetrical.

TamiyaW1688

iTrader: (16)

It is very interesting. Can you take pictures from top too?

h2e

TamiyaW1688

iTrader: (16)

Thanks, just got the MSX. Thinking to buy TRF420 servo mount so I can mount the servo position forward. But it seem do the same if I do like you.
Question, is Tamiya trying to moved spur forward to improve traction? What you doing will be same as MS.

h2e

Well the drivetrains of the 420X and TA07MSX are quite different in their approach.
The TRF420X needed the spur further forward to have more similar belt lengths to have a similar response time of the front and rear axle. As they kept the motor position almost equal, the fore/aft balance was not much affected. The 420X allows for a really narrow spacing between the battery and motor.

The TA07MSX, as it was originally sold, has the single belt routed, such that
a) on acceleration, the rear axle sees drive first, and the front comes 257mm of belt length (stretch) later.
b) on deceleration, the front axle would see braking torque first, and then 257mm of belt length (stretch) later, the rear would brake.

But yes, I did this change to allow for the forward mounted servo mount, as you state, because some people say it gives more steering.

What I am now curious about: Which of the three motor positions are good?


3 kinds of Single-Belt chassis. Left: h2e five, middle: Tamiya TA07MSX with inverted drivetrain, right: Tamiya TA07 with inverted drivetrain.

Right: The TA07 was a bit of a handful on high grip carpet, with typically too much steering. On asphalt a biest with the right amount of steering especially on-power. It has the motor the most rearward of the three (one of the reasons why the TRF420X should be still a great car on asphalt),
Middle: The Tamiya TA07MSX has an inverted battery/electrics position, to allow for the forward mounted servo mount. The drivetrain is similar to the other two cars, but has the motor most at the front and the spur behind. The motor sits almost perfectly on the fore/aft CoG line, which should be good for inertia and thus chicanes etc.
Left: The h2e five with the motor between the two other cars is really balanced, but a bit understeery on carpet.

Considering belt lengths between the spur pulley and spool/rear diff, the following lengths are measured:

Car: h2e five ¦ TA07 MSX ¦ TA07 ¦
Belt length to front @ braking [mm]: 120 ¦ 155 ¦ 137
Belt length to rear @ braking [mm]: 377 ¦ 412 ¦ 394
Belt length to rear @ accelerating [mm]: 205 ¦ 195 ¦ 195
Belt length to front @ accelerating [mm]; 462 ¦ 452¦ 452

This means, given all things equal (i.e. axle weight balance), the h2e five should give the most stable braking (as its front reacts first of the trio), and on-power it should be similar to the other two. Interestingly all cars are relatively equal on-power, despite different motor and pulley positions, due to different distance between motor pulley and counter pulley.

Does this make sense?

h2e

Sorry, I completely overread your post. You need to make a new topdeck if you want to flip the drivetrain. For me that's two wins at once (servo and other belt routing), that's why I did it.

TamiyaW1688

iTrader: (16)

Thanks for engineering analysis, I'm engineer myself and I like to read your post and analysis.

TamiyaW1688

iTrader: (16)

I'm running the MS right now, not sure I can feel any different than MSX.

sosidge

Are you running the motor in reverse to get it work when fitted on the wrong side? How are you compensating for the sensor position?

h2e

Sorry, so far it's just a mockup and I haven't run the msx yet. too nice to scratch

Airwave

iTrader: (1)

I understand how it is reducing there two effects? Could you please explain why?
I was under the impression that with this implementation you are still pulling the belt from the rear differential, so it should not change anything...


I would have imagine that you need this kind of belt layout to ensure that you are first pulling on the front instead of the rear

But it would be ridiculous and it would limit the size of the spur gear to very small models

YFB

TRF420X vs TA07MSX

Enjoy the video.

zaraz

iTrader: (38)

awesome video

MadMac_1977

great video - thanks for sharing

liteweight

iTrader: (12)

guys where can i get aluminum chassis for msx?