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XV-mini - development of XV-01-based 4wd mini chassis

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So this is a project I've been working on for a while, although I got distracted by other project lately, so it's still in very early stage. Anyway, inspired by @wtcc5's thread, I decided to make a parallel topic that follows development of a different kind of a 4WD mini chassis :) Hopefuly I'll be able to finish it.

The idea for this chassis was born at the end of the last year - I wanted to make something more advanced than my MF-01X. The main inspiration is differential in M-07/8, which is the same as XV-01, and long suspension arm design in M07/8, which works much better for rally than the older M05Ra one. I thought that I could use top halves of XV-01 gearboxes with custom bottom halves, which would serve as mounting points for M-07 suspension arms.

Well, that didn't work and I had to change the motor position using custom top portion of the gearbox. And just when It started to look interesting, Tamiya decided to announce the XM-01... I was thinking about ending the project... but realized, that thre's still a point in continuing - XM-01 will allow me to skip design of the bottom gearbox part thanks to the new suspension design, and I can focus on making my designs compatible with a full scale XV-01.

Full scale XV-01? Yes, my plan is much bigger than just shrinking XV-01, that's just one of the three big changes to the XV-01's design. Can you guess the other two? This picture might provide a little hint:

1605260458_XV-minigearbox.png.eba6ddc028d00431d2fb984207421a5f.png

It is nearly finished design of the gearbox. I needed to get the motor lower, unfortunately doing that with the stock gearbox would limit the available gear ratios. So I added another idler, which allowed me to reuse the stock motor mount. You can see that it created another issue, but in fact, it's not an issue at all. Can you guess why? :)

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Very cool, keep motivated with this despite the XM-01! 

Have you brought the motor in-board between the axles, instead of hanging out over the front axle? That's pretty cool. I reckon you could mill the motor mount out of flat sheet metal too for added strength. 

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1 minute ago, ChrisRx718 said:

Have you brought the motor in-board between the axles, instead of hanging out over the front axle?

Thank you for your support :)Correct, this is the rear gearbox :) The front will remain stock, just flipped around. I was thinking about front-mid position, but that would be too complex, if not impossible. This variant should fit Embie's conversion chassis after some adjustments.

14 minutes ago, ChrisRx718 said:

I reckon you could mill the motor mount out of flat sheet metal too for added strength. 

The motor mount is re-used from the stock chassis. I try to use stock parts wherever possible to make my designs more accessible.

now, can you guess the other change to XV-01 design? 😁 

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This is very interesting. Are you making a mid-rear motor 4wd with the belt going over the motor?

If you added an idler to the rear gearbox, how are you going to keep the front spinning in the same direction if you used the stock gearbox in the front?

And you are speaking about Embie racing chassis. Are you utilising the short wheelbase (237mm) version with the XM-01 arms?

I wonder how are you going to fit the electronics there? I am currently building a full size Embie racing XV-01 all-in-one kit with a rear-mid motor RWD, and there is not big amounts of space available for the ESC and receiver. I probably have to have them hanging over the edge of the chassis plate.

 

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Actually now I figured out that the spinning direction issue is not an issue at all, if you still have the rear gearbox output shaft for the pulley in the original place. But it seems to me that you have added two additonal idlers, based on the outside appearance of your gearbox. Do I make a wrong assumption here?

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41 minutes ago, Verskis said:

This is very interesting. Are you making a mid-rear motor 4wd with the belt going over the motor?

Almost, this will be an option if the other solution doesn't work. That's the reason why both idlers are on the same level.

43 minutes ago, Verskis said:

And you are speaking about Embie racing chassis. Are you utilising the short wheelbase (237mm) version with the XM-01 arms?

Embie chassis is meant for full scale variant. The mini variant will use custom chassis - the exact design is still something I have to decide, but I'm thinking about similar concept to my rally chassis prototype - aluminium "backbone" with 3D printed side guards to create the bathtub.

46 minutes ago, Verskis said:

wonder how are you going to fit the electronics there? I am currently building a full size Embie racing XV-01 all-in-one kit with a rear-mid motor RWD, and there is not big amounts of space available for the ESC and receiver.

The plan is to have a shorty transverse battery, similar to MF-01X. Another option would be longitudinal position, but slightly shifted to the side to make space for the servo and electronics next to it. There's no belt or driveshaft in the way, so there's a lot of freedom in electronics layout.

43 minutes ago, Verskis said:

Actually now I figured out that the spinning direction issue is not an issue at all, if you still have the rear gearbox output shaft for the pulley in the original place. But it seems to me that you have added two additonal idlers, based on the outside appearance of your gearbox. Do I make a wrong assumption here?

The opposite spinning direction is actually necessary for what I want to do. I added only one idler, in combination with lowered motor plate/spur layshaft, it moved the motor quite far in the front direction, which is why it might appear that I added two idlers.

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@ThunderDragonCy Hint: take a look at MF-01X 🙂 I thought that not fully revealing my plans would lead to an interesting discussion and might lead to new ideas :) Like your comment, I didn't even realize that I made a 4-gear modification 😁

Once I get the model to presentable state, I'll show it 🙂

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Some progress on the gearbox, so I can reveal the second big change to XV-01 - in order to clear the motor, the belt would have to be lifted by a centimeter or so - which is not impossible, since the bottom of the belt is the slack side with the motor in the back - but I didn't like the idea. So I chose a different approach. This is why I needed the second idler that rotates in the opposite direction :)

The shock tower mount is designed for stock rear tower.

1901507597_XVgearbox.thumb.png.8ddb780c95ee04bea434aa99b467f71e.png

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I'm very impressed by your skills and creativity, but can't help thinking that adding even more gears to allow for a shaft drive makes this thing a bit of a Rube Goldberg machine...

 

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30 minutes ago, Verskis said:

I'm very impressed by your skills and creativity, but can't help thinking that adding even more gears to allow for a shaft drive makes this thing a bit of a Rube Goldberg machine...

The alternative would be belt with 2 extra pulleys to get over the motor and hoping that it won't crash into itself :D 

Overall it's less complicated than MF-01 or TA02.

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I'd love to see an updated and stronger TA-02 drive line.   Do you think its possible to make a M chassis TA-02 style car, but using XM-01 suspension?

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7 minutes ago, Wheel_Nut said:

I'd love to see an updated and stronger TA-02 drive line.   Do you think its possible to make a M chassis TA-02 style car, but using XM-01 suspension?

That's exactly what I'm trying to make. The overall layout will be similar to my MF-01X conversion, but with bathtub-style chassis, which would provide some cover for battery/motor/electronics. 

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It's been a while, but I did some work on the design. I decided to give a try to belt variant first.. and it looks like it could work. I still want to do shaft driven variant as well, I just need to get some TD4 parts.

IMG-20240509-WA0000.jpg.489b5173b911b0900addf122adc4c711.jpg

Back in march, I even tried to print one of early iterations to test how it fits with stock parts. It does quite well :)

Resize_20240329_181815_5162.jpg.5c173c74eb24265bee0d71fa7049849e.jpg

Still deciding whether I'm gonna use M-07 or XM-01 arms. I still like the former more, even though it means that I'll need custom gearbox bottoms.

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I noticed the XM-01 suspension mounts are located on the end of the pins which is typical of touring car racing chassis.  Due to the wider spacing of the suspension mounts I think they are less likely to fail due to crash damage.   If so, it could be an advantage of using the XM-01 style arms.

The M-07 suspension mounts are available as fibre reinforced injection moulded parts from Tamiya, which I'd expect to be quite strong.  I don't know if you intend on using these items from Tamiya.  If making 3D printed suspension mounts, it could be a possible failure point, but it obviously depends on the material.

 

 

 

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2 hours ago, Wheel_Nut said:

noticed the XM-01 suspension mounts are located on the end of the pins which is typical of touring car racing chassis.  Due to the wider spacing of the suspension mounts I think they are less likely to fail due to crash damage.   If so, it could be an advantage of using the XM-01 style arms.

Yes, they use same suspension mounts as XV-01/2, which gives quite wide variety of suspension mounts. I assume they'll use fibre reinforced plastic as XV-02. The disadvantage is, that the arms have no droop settings and suspension mounts are wider than M-07/8 style, giving slightly shorter arm.

2 hours ago, Wheel_Nut said:

The M-07 suspension mounts are available as fibre reinforced injection moulded parts from Tamiya, which I'd expect to be quite strong.  I don't know if you intend on using these items from Tamiya.  If making 3D printed suspension mounts, it could be a possible failure point, but it obviously depends on the material

For the rear, I intend using Tamiya parts. I can use M3 nuts or metal columns inside 3D printed parts they'll mount to to make them stronger.

For the front, I'm not sure yet, but using Tamiya mount could be a viable option.

This solution would provide longer arms and downstop setting, as well as easier rear toe-in setup. I intend to use XM-01 uprights, if they are compatible with M-07 arms.

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Thanks for explaining the benefits of the M-07 arms.  It sounds good to me if you are able to accomodate the Tamiya M-07 front suspension mount or some metal reinforcement.

To adjust maximum droop on the XM-01 arms, it could be done the old fashioned way of building spacers and O-rings internally on the shock shaft as done on earlier M series cars.  Obviously the screws are more convenient.

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The TT02 diffs are pretty big compared to other 1/10 offerings. Perhaps using a 1/10 buggy diff or even a 1/16 buggy diff would allow you to have longer arms and more suspension travel. Some people have put 4s plus through the small 1/16 buggies and they've held up ok so going down the micro scale route shouldn't cause any strain issues. 

I was disappointed when I saw the XM-01 has no droop settings, that might of been down to them having to squeeze a tt01 diff in there. 

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1 hour ago, Alex97 said:

The TT02 diffs are pretty big compared to other 1/10 offerings. Perhaps using a 1/10 buggy diff or even a 1/16 buggy diff would allow you to have longer arms and more suspension travel.

It's based off XV-01, so it does have buggy diffs :) I also didn't like the large diffs on XV-02/XM-01. 

1827875265_TamiyaM08buildreview014(Custom)-1.thumb.jpg.22f7af2be072d19e2a25eb6982455b74.jpg

M-08 uses the same diff, so It should be possible to replicate this setup, (photo by @qatmix) with arms quite close to the diff.

1 hour ago, Alex97 said:

I was disappointed when I saw the XM-01 has no droop settings, that might of been down to them having to squeeze a tt01 diff in there. 

XV-02 doesn't have downstops either, even thou arms support it and all that'd be needed to make them work would be a slightly different skidplate.

Use of XM-01 arms would be shortcut that'd allow me using stock XV-01 gearbox bottoms and simpler chassis plate. But I like M-07/8 arms, so I'll probably do the more complicated route :)

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We hit a big milestone today, with prototype of functional belt drivetrain on a full-scale XV-01 chassis.

Resize_20240601_151950_0172.jpg.51ac0b8951f3b5fd0eddf914fdceb579.jpg

It wasn't build by me, but by a friend, who had parts lying around and was kind to send me these pictures for sharing.

He has been interested in mid-motor conversion for some time, which actually gave me the idea for this whole project. I got some feedback on the model, luckily only minor tweaks were needed to get it working.

Resize_20240601_151950_0820.jpg.9b7b1e2a14cddb40050aa601eeca2a2a.jpg

I was happy to see that the stock motor plate fits perfectly. I just need to model a spur cover.

Resize_20240601_152201_1211.jpg.2eac95e47e771da1673eced3274d8ef1.jpgResize_20240601_152200_0807.jpg.6fbd8a4551faa7c78ebe9982900f0035.jpg

Using stock tensioner assembly with 630 bearings, belt is quite close to the motor, but it doesn't rub even with loose belt. In the case where vibrations would cause contact with the motor, larger bearings can be fitted to keep the belt further away from the motor.

Now I need to get TD-4 bevels and counter shaft for the shaft driven drivetrain

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