To complete the work with this MTC (Monster Truck, Crawler) Chassis I had to design some rigid axles, a multilink suspension system and a compatible universal shaft. With these new parts I think you can build a pure Crawler or a Scale RC.
The parts in this publication will let you build a car with a wheelbase from 290 to 330 mm. Maybe 270 mm wheelbase or 280 can be achieved with a sourced universal shaft transmission. The same way you will be able to choose between four different axle widths using the same sourced parts than in previous MyRCCar chassis publications.
A build with rigid axles will use less sourced parts than a independent suspension one. The steering system is much simpler; you won't need bearings for it. The axles assembly is also simpler but there is a little extra hand work while assembling the links.
There are no oficial videos from this Rigid Axles Version by now. Please, subscribe to my Youtube Channel to be updated with the latest videos!
Step 1: Characteristics and Options
The main chassis
One of the best things is the main chassis remain the same, compared to the independent suspension version, so you can convert one or both of the axles to a rigid axle version! The Side bars, the central platform, the gearbox or the top covers are used the same. The front platform is also re-used in other position and the rear one is not necessary.
As you can see there are 3 different center parts for the axles. This will give you 3 different widths for your axles... You just have to choose. But there is also a wider one using the long axle and the "long C-Hubs" or "long rear fixed blocks".
- You can use 4 different CVDs with the long axle plus 2 more with the long c-hubs
- You can use 2 different CVD combinations with the medium axle
- You can use 2 different CVDs with the small axle
The same sourced parts are used for this build, so I have designed different c-hubs, steering blocks, rear fixed blocks and steering plates to use them in this axles.
- There are 2 different C-Hubs, the long one is only for HSP 108015 and HSP 188015
- There are 4 different Steering Blocks, the same types than in all MyRCCar publications
- There are 6 different Rear Fixed Blocks, 2 of them longer for HSP 108015 and HSP 188015
- There are 4 different steering plates or "bars", one for each axle width. XL, L, M and S
Please take a look to the first drawing for more info.
These links are Print in Place ball joint articulated. I use to print with -0.02 horizontal expansion to get the correct results, this time i printed them with -0.03 to be sure i could unlock them.
I have created some fixed length links and other parts to build variable length links.
This links have to adapt to the chosen wheelbase, from 145mm PWB to 165mm PWB. But also they have to adapt to the different axle types, the long, the medium and the short one. There are also 2 possibilities to assemble the bottom links in the long axle; you can mount them in the outer holders of the axle or the inner ones.
But resuming, using the variable length ones, which are available in 2 lengths and for M3 or M4 screws, you will be able to have any of the needed measures.
Use the second and third drawings to choose the right length for your wheelbase and axle width.
The Universal Shafts
If you have the typical sourced parts for the MyRCCar projects, as 02024 with pinion and universal 1/10 vase for the F/R diffs, and a 1/8 center diff as the Trooper or the SST ones, then you can use this transmission.
The Locked 3D Printed Differentials
If you want to go "extra-cheap", you can't wait for your sourced parts to come or if you want a full-locked transmission system then you can print a center differential, Mod1 46T, and also a F/R diff. compatible with HSP 02024. That means you could replace all the diffs with 3d printed ones.
More info about sourced parts, prices, printing tips and more!
Remember I have done all MyRCCar projects around the same sourced parts, 1/10 typical ones. Please, take a look to my previous publications, MyRCCar OBTS Chassis and MyRCCar MTC Independent Suspension Version
I recommend you to take a look to them to have a better global view about what can you do with this projects.
You will also find at the end of those publications a lot of printing tips which are of course also valid for this Rigid Axles Version.
Step 2: Main Chassis Assembly
Printing first parts to start
This time I'm going to list the parts and the number of them you need to print. If you have to choose between versions of a part you will find an "*" in that part.
Remember that every time you have to print a part various times is better to print first just one, test it and then print the clones.
I'll try to reflect the order I would use to print them and assemble them, but of course you can do it in your own order. There we go!
For the first step you will have to print the next parts:
- 2x MRCC_MTC_CentralSideBar
- 4x MRCC_MTC_FrontRearSideBar
- 1x MRCC_MTC_Platform_Central
- 1x MRCC_MTC_Platform_Front
- 2x MRCC_MTC_Platform_Holder
- 1x MRCC_MTC_RigAxles_Links_FrontPlatformHolder
- 1x MRCC_MTC_Cover_TopCenter
- 2x MRCC_MTC_Cover_TopFR
- 1x MRCC_MTC_RigAxles_TopBatteryBox
- 4x MRCC_MTC_ShockHolderPair0cSTRONG
- 1x MRCC_MTC_CD_GEARBOX_BOTTOM_V3
- 1x MRCC_MTC_CD_GEARBOX_TOP
- 1x MRCC_MTC_CD_ADAPTOR *
- 1x MRCC_MTC_CD_GEARBOX-> Gears, pinion and axle *
I would start assembling the gearbox. As you will probably want a "Crawler Style" chassis you will want to use the gearbox reduction. So first of all, go to the end of my previous MTC Chassis Publication to see how to print the right parts for your desired gearbox. I would also mount the motor in the gearbox and do my first tests with it to see if everything is working fine.
After that, use the provided drawings to see how to assemble all the previously printed parts into what I want to call the "main chassis". Many of these parts can be used to build the other version of the MTC Chassis.
Step 3: Axles and Links
Printing Axles and Links
Most of the main chassis parts were "standard" with no options. This time is the opposite! You need to know which axle width you want and what wheelbase you want. If you have already chosen between the axle widths options, the wheelbase and CVDs ones, then you are ready to print the next parts! Remember the "*" means options!
To build your Axles print the next parts:
- 2x MRCC_MTC_RigAxles_Axle_Bottom *
- 2x MRCC_MTC_RigAxles_Axle_Top *
- 2x MRCC_MTC_RigAxles_Steering_C-Hub *
- 2x MRCC_MTC_RigAxles_Steering_SBlock *
- 2x MRCC_MTC_RigAxles_Steering_FixedBlock *
- 1x MRCC_MTC_RigAxles_SteeringPlatform_*_Adjustable *
- 2x MRCC_MTC_RigAxles_Links_Holder_CenterPlatform_pair
- 1x MRCC_MTC_RigAxles_Links_Holder_TopCover
- 4x MRCC_MTC_RigAxles_Links_Adj_66dot5to85 *
- 12x MRCC_MTC_RigAxles_Links_Adj_87dot5to112dot5 *
- 1x MRCC_MTC_RigAxles_BallJointExtreme_70mm
- 1x MRCC_MTC_RigAxles_BallJointExtreme_Normal
Once you have everything printed is time to assemble the axles and the links! Let's first focus in the first part.
To start, insert the 5x10x4 bearings in the Axle top parts. Then insert the HSP 02030 pinions or similar and use your Universal 1/10 cup / vase to fix them in their place.
Go on putting your HSP 02024 or similar F/R differential in its place in the axle top part. Adjust its position with the provided "washers" for the best fit with the pinion.
Now put the axle bottom part to close the axle and see if the differential fits well enough. You will probably have to clean a little the inside zones of the axles where 3d printing bridges are made. The perfect cylindrical shape to house the 10x15x4 bearings of the diff is really hard to print so... clean it with a X-acto knife!
When you have both parts of the axle fitting good and you can feel the pinion and the diff. spinning nice, use the four central M3x10 counter-sunk screws to close the axle.
You can put the front C-hubs in their place in the front axle using the proper screws. Then you can mount the proper 5x10x4 and 10x15x4 bearings in your front steering blocks and rear fixed blocks.
And now is when comes the tricky part! You have to put the axle in vertical position to insert one of your CVDs by the side "hole" of the axle. Let it fall inside and be sure the pin on the head of the CVD is inside the diff output vase. Then try to pass the CVD outer part through the front steering block or the rear fixed block without moving it much and try to get the part to its final position with the CVD inside...
Find the patience to do it for the four wheels! It will be also harder if you are using rear wheel cups+dogbones instead of CVDs... in that case this step turns into ART!
Now let's center on assembling the links with the axles. You will need some spacers for the link holders. I use some silicone tube about 3mmID 5mmOD and I cut about 1.5mm slices. I use 2 slices for each link holder, to the axles the same than to the chassis.
If you have your shocks around there, is better to mount them now with their lower part in the axle so you can assemble the lower links to the axle.
I suggested you to print the adjustable version of the links. You will have to assemble 2 "heads" with a M3x50 or M4x50 screw (for the long ones) and M3x40 or M4x40 for the short ones. Screw and adjust them to be the right length you need for your wheelbase. I think this will give you some freedom to change your wheelbase with very little mods and no re-printing.
Use the last two parts of the list to assemble the servo link with a long M3 screw. This one will probably be the last one you assemble into the chassis.
Step 4: Final Assembly
If you have your "main chassis" and your axles... What more do you need?¿?¿? Nothing!* Just assemble them together!
You will have to partially un-screw the 30mm long side screws from the front part of the main chassis to be able to assemble the other extreme of your front upper links with the chassis. Use the same silicone tube slices than before.
Inserting the central platform holders in their places should be easy. Use the proper screws to fix them in place.
It won't be so easy for the rear upper link holders. There is no hole in the top cover to fix them, so you will have to do them. Find the best place for the holders sliding them through the rear top cover sides. One you have it, mark the top cover with something trough the holder top holes and then use something to make the holes in the marked places of the top cover. Once you have the holes, fix the rear upper link holders in their places with the proper screws.
You almost have it! Just screw the top part of your shocks to the shock holders with M3x20mm Socket Head screws and maybe add your wheels to feel for the first time the height, weight and suspension system of your machine :)
Now put the rest of the electronics in the car. That means holding the Servo with four M3x12mm screws and maybe using the Servo Spacers to bring the servo's final position to the front. You can use some double side tape to put your ESC and Receiver over the top front part.
Step 5: The Universal Shaft
Now you will understand why I used an "*" after "Nothing!" in the previous chapter... You have functional F/R axles and a working gearbox but... As the distance between the center diff. output vase and the F/R diff. input vase changes while suspension system is in action we cannot use a simple "dogbone" as our central transmission.
I did my best to design a double cardan variable length transmission to be used with this chassis to solve the problem without sourcing this parts. Anyway, I could not try sourced metal universal shafts but I'll do. This 3d printable version can do some work but you must build it very good to have normal results, not very good ones.
The main Idea is to print two cardans for each shaft. One must go in the normal 1/10 F/R input vase and the other in the center diff output vase. In the first one you must mount the inner part of the transmission axle and in the other the outer part. You must choose the right length of this parts for your wheelbase.
There are 4 types of forks, they are:
Fork1, for 1/8 diff. This one goes into the 12mm output vase of the center diff and uses a M3x18mm Countersunk screw to act as torque transmitter and also to fix the fork to the vase
Fork2, connected with the Fork1 with the 11mm cube and 3mm piano wire portions, one 3x18mm piano wire part and two 3x7mm parts. I originally designed it to use M3x8 grub screws but they get out of place after some play, so better piano wire and “Loctite” them. This fork also connects with the 12mm outer axle.
Fork3 is the one to mount on the 1/10 input vase of F/R diffs. Use a M4x5 grub screw to fix the Fork to the vase
Fork4 connects with Fork3 with same method than F1 with F2, and with the 10mm inner axle. Use M3x16 countersunk screws to fix the inner and outer axles to F2 and F4.
Take a look to the names of the different inner and outer axles of the universal shaft to have a clue about which ones you need for your wheelbase and riding height!
Use M3x16 counter-sunk screws for assembling the inner and outer parts to the cardans, and also to fix the cardans in the output vases of center diff. Use M4x5 grub screws to fix the other cardan to the input F/R diff. vases.
If you try to use sourced universal shafts you won't need the F/R 1/10 universal cups / vases as one of the sides of the sourced universal shaft will be mounted instead. Maybe designing an adaptor you can "plug" the other side of the universal shafts to the center diff. output vases. By now, you can use a 3d printed locked center diff with some modifications with some 5mm piano wire as the only maker by now of this kind of chassis already did. Take a look to his build and some of his videos here, the only ones by now!
Step 6: The Locked Differentials
The fake SST Locked Differential
Just two parts which must be assembled with two M3x8mm countersunk screws. Then use the normal adaptors and 12x18x4 bearings for your SST diff and mount the fake fixed diff. into the gearbox.
Now there is also another version of the axle to be mounted with 10x15x4 adaptors for the gearbox but the same crown gear. Using the four types of Forks, you should be able to build a universal shaft with the right kind of fork for the 10mm center diff shaft, or you can use the standard one if you use the SST replacement with 12mm axle.
ATTENTION: The position of the motor is very important, and I have designed it to work with the gearbox and 14T pinion for the motor attacking a 28T gear. If this parameters changes then the motor can touch the universal shaft or the lower links, the space is very important in this build!
The fake HSP 02024 Locked Differential
I have made a compatible 3d printable version of the Front / Rear differential, but is a very simple locked version. As many of the people interested in this Rigid Axles Version will want it for crawling, I hope they can give a try to this locked differential. It consists in an axle, a gear and 2 covers for the axle vases. I only publish this 3d printable diff. with this Rigid Axles because is the only scenery in which the CVDs are always aligned with the diff vases, so there is a lot less stress than in other situations.
I could not imagine the effect of the differential until I try to drive without it... OMG I could not expect that extra bad turning...the wheels sound like in a parking when steering and the radius of the circle is extra big compared to the same car just using not locked diffs.
So... how much plastic do you want in your build?¿? This time is more up to you than ever!
Step 7: Files and More!
You can find all STL files for print in one compressed file. The files
has the same license type than this instructables or the other places where they are hosted. Remember you don't need to print all parts in the file, just the ones for your customized build ;)
And Those Were All MyRCCar Chassis Options by Now... :(
I remember you here all the options you have to build your RC Car with MyRCCar projects:
Build On-Road RC Car with MyRCCar OBTS Chassis + Tesla Body with Lights
Build Off-Road RC Car with MyRCCar OBTS Chassis + Buggy / Truggy Shell, Wing, Bumper and Lights
Build Off-Road RC Car with MyRCCar MTC Chassis Indpendent Suspension Version + Typical Pickup or FJ Cruiser Body
Some more work need to be done!
I really enjoy designing and improving these things. I think having the right skills to do it is not for everyone but the testing and improving capabilities are in most of us!
You can't imagine how happy I feel when I see someone as Botyoyo, Saccco or Mario from thingiverse improve or create new parts! Working for no one and everyone same time is a weird feeling you must taste!