Build Thread 1:12th Scale Rollback Truck Ideas

[James A. Doty]

I found an stl file for rims I'll be using. I think they'll look great.

I have the parts off the print bed but haven't had time today to remove all the support material and put them together.

 

[James A. Doty]

Here's two of them ready for screws. I have enough M2.5 screws but they're all too short, so I'll have to order more of them. At least 36 of them.

Also, this is turning into a 1:15th scale rollback truck, unlike my initial desire for 1:12th scale, I decided to use the chassis from a WPL B16 and it's left and right wheels aren't far enough apart to make the truck larger without it looking odd. Still, I'm making progress.

Major items left to do:
design and print mount for lift servo
finish designing and print the front cab to chassis mount
design and print the sub-frame for the rollback bed
design and print a headache bar for the back of the cab
design and print a holder for the battery, receiver, and esc

 

[WickedFog]

Looking great so far!

 

[James A. Doty]

The rims I chose kept breaking when I tried to put them together so I found one piece rims I liked and printed them, it was a single tire rim and a dually rim. The dually rim worked great, I printed four of them. But the single tire rim is the wrong size for the WPL C94 tires I'm using for the front axles.

So I spent the last two days designing new rims for the front axle. I have one printing now in draft mode to see if they'll work for me. If they will I'll design dually rims for the back axles.

 

[James A. Doty]

I think I've finally finished the mods needed to use the WPL B16 chassis. The rear wheels are moved back, I've installed a longer driveline to go from the gearbox back, the two speed gearbox is setup and the servo is properly adjusted, and I designed rear rims that fit the front tires of the WPL C94.

I'm not 100% happy with my electronics tray so I redesigned it but I'm waiting for four rolls of PETG I ordered to arrive so I can print it.

I'm measuring out the dimensions I'll need for the sub chassis the flatbed will sit on. I need to design the sub chassis so neither it or the bed have clearance issues with the electric motor and gearbox. I also need to design the servo carrier for the tilt assembly, but need to get the sub chassis designed first.

I've designed the front cab mounts and will print them when I print the cab since they're integrated.

I think my rim designs are fantastic, they're currently my favorite part of the build. Those rims were the most challenging parts I'd ever designed in Fusion. It's a bit of a challenge to mount the tires on the dually rear rims, but worth the effort.

I'm a putz, you can see in the photo that I didn't make the opening in the back of the electronics tray large enough to get more than one servo cable through it. I need to get no less than four servo cables through it.

I'm trying to leave enough room above the electronics tray to add a partial interior to the cab. Maybe I should start over on the electronics tray and design it so the battery is centered so it would fit under the engine hump in the cab.

I'd have to do something about the giant eight channel receiver. I have a slightly smaller ten channel receiver I wanted to use but it won't work with the RadioMaster MT12.

 

[CertifiedMike]

I think I've finally finished the mods needed to use the WPL B16 chassis. The rear wheels are moved back, I've installed a longer driveline to go from the gearbox back, the two speed gearbox is setup and the servo is properly adjusted, and I designed rear rims that fit the front tires of the WPL C94.

I'm not 100% happy with my electronics tray so I redesigned it but I'm waiting for four rolls of PETG I ordered to arrive so I can print it.

I'm measuring out the dimensions I'll need for the sub chassis the flatbed will sit on. I need to design the sub chassis so neither it or the bed have clearance issues with the electric motor and gearbox. I also need to design the servo carrier for the tilt assembly, but need to get the sub chassis designed first.

I've designed the front cab mounts and will print them when I print the cab since they're integrated.

View attachment 275956

I think my rim designs are fantastic, they're currently my favorite part of the build. Those rims were the most challenging parts I'd ever designed in Fusion. It's a bit of a challenge to mount the tires on the dually rear rims, but worth the effort.

I'm a putz, you can see in the photo that I didn't make the opening in the back of the electronics tray large enough to get more than one servo cable through it. I need to get no less than four servo cables through it.

I'm trying to leave enough room above the electronics tray to add a partial interior to the cab. Maybe I should start over on the electronics tray and design it so the battery is centered so it would fit under the engine hump in the cab.

I'd have to do something about the giant eight channel receiver. I have a slightly smaller ten channel receiver I wanted to use but it won't work with the RadioMaster MT12.

Are you sure the receiver won't work with the MT12? Just wondering.
Ultra compatability is one of the greatest features on the MT12!

The chassis is looking great! Nice work!

 

[James A. Doty]

Are you sure the receiver won't work with the MT12? Just wondering.
Ultra compatability is one of the greatest features on the MT12!

The chassis is looking great! Nice work!

Thanks, the chassis' from a WPL B-16, though I did move the rear axles back as far as I could without drilling new holes.

The ten channel receiver I was going to use is a HotRC F-10A. I was stunned to find a ten channel receiver for under $9.00. That's crazy. All the looking around told me it couldn't be done, so I'm just not sure. In the process of trying to make the F-10A work with my transmitter I did install the most recent updates for my MT12.

I'm still a novice when it comes to setting the MT12 up but I've learned a lot and I absolutely love that radio. But I never did find a way to bind it to the HotRC receiver. I have the MT12 4in1.

I'd like to buy the ELRS add on, but admit that I'm not really sure which one the MT12 4in1 uses. I think it's the Ranger Nano though.

 

[CertifiedMike]

Thanks, the chassis' from a WPL B-16, though I did move the rear axles back as far as I could without drilling new holes.

The ten channel receiver I was going to use is a HotRC F-10A. I was stunned to find a ten channel receiver for under $9.00. That's crazy. All the looking around told me it couldn't be done, so I'm just not sure. In the process of trying to make the F-10A work with my transmitter I did install the most recent updates for my MT12.

I'm still a novice when it comes to setting the MT12 up but I've learned a lot and I absolutely love that radio. But I never did find a way to bind it to the HotRC receiver. I have the MT12 4in1.

I'd like to buy the ELRS add on, but admit that I'm not really sure which one the MT12 4in1 uses. I think it's the Ranger Nano though.

I don't own an MT12 but I sure do like them! I am not really into programming stuff. My laptop isn't even on line. Lol!

I don't know which ELRS is correct either.


$9 is crazy cheap for a receiver! I hope you can find a way to make it work!

 

[James A. Doty]

I've made some pretty good progress. I printed the sub chassis today but missed four things in the design so I'm printing it for the third time.

I have the incorrect sub chassis mounted so I could check for other issues. It's almost a perfect fit, the slight redesign resolves that.

Then I have to print the scissor mechanism, make final adjustments to the pivot servo mount, print a hinge pin for the pivot at the back, mount the sub chassis to the chassis, print the scissor mechanism, and mount the sliding bed on the frame it sits on. I should get about 30mm of front to back travel. I'm worried about the bed height though, if it can't contact the ground with only 30mm of travel and I'm going to have to completely redesign the sub chassis and will have to print it on my Troodon V2.0 Pro since at the moment it just barely fits the bed on my Bambu Lab P1S.

Once all the mechanical issues have been resolved I can print the cab then wire everything up.

 

[James A. Doty]

So close! except for the cab I'm printing all the remaining plastic parts of the truck, including printing the electronics tray again because I've been struggling to make it level on the chassis. I'll live with how ever the current print of the electronics tray goes as long as the print is good.

I'm reprinting the lifting servo mount because I decided to add some cable management to it. I'm also printing the lower and upper pivot bars, the pivot nut holder, and the four pivot arms. Hopefully I don't have a design issue with my sub chassis, though it's an easy part to make corrections to.

I took some measurements the bed can slide forward and backward 65mm which in full scale would be about thirty inches. The angle is a bit steep though. I might have to do some additional modelling later on to allow the bed more room to slide back but that would involve making the chassis longer by a lot (I haven't measured it, redesigning the sub chassis moving the twin axle rear end back, and finding a much longer rear drive line. I'm not sure I'm ready for that just yet. I did check measurements to see if I could make the flatbed a bit lower, but there just isn't room to do so. Also I don't have space on the twin rear axles to mount them above the leaf springs even though I'm pretty sure I can do that with the front axle.

I'd like to do lights, I've done some research but I have to admit I'm confused on the whole light setup thing. I bought two six channel receivers with built in two pin light control sockets, the Dumborc P6DCG, but have no idea what light sets it'll support. I also bought an amber emergency light bar for on top of the flatbed, the instructions said to plug it into a servo channel and use that channel to control it but it didn't give any specifics on channel setup involving if it's just a trigger to turn the lights on then they do their own thing or if the light bar acts as a servo would and changes modes by reading proportional control movement, like the steering and throttle do. I do know this though. I plugged it into a servo port on my receiver and it came on, but even though I set up that channel on my MT12 transmitter to just trigger it on or off, it just sits there doing patterns for a few seconds then locks up, and it drains the poor battery that came with the WPL B16 truck I've stripped down as the donor vehicle within five minutes.

If I could figure out what light kit the P6DCG supports I could go ahead and design the cab to fit those lights and print a tail light mount for the rear of the truck.

I also need to find a 1:12th to 1:15th size winch kit to add to the front end of the flatbed.

Still, this is a fun project.

 

[CertifiedMike]

So close! except for the cab I'm printing all the remaining plastic parts of the truck, including printing the electronics tray again because I've been struggling to make it level on the chassis. I'll live with how ever the current print of the electronics tray goes as long as the print is good.

I'm reprinting the lifting servo mount because I decided to add some cable management to it. I'm also printing the lower and upper pivot bars, the pivot nut holder, and the four pivot arms. Hopefully I don't have a design issue with my sub chassis, though it's an easy part to make corrections to.

I took some measurements the bed can slide forward and backward 65mm which in full scale would be about thirty inches. The angle is a bit steep though. I might have to do some additional modelling later on to allow the bed more room to slide back but that would involve making the chassis longer by a lot (I haven't measured it, redesigning the sub chassis moving the twin axle rear end back, and finding a much longer rear drive line. I'm not sure I'm ready for that just yet. I did check measurements to see if I could make the flatbed a bit lower, but there just isn't room to do so. Also I don't have space on the twin rear axles to mount them above the leaf springs even though I'm pretty sure I can do that with the front axle.

I'd like to do lights, I've done some research but I have to admit I'm confused on the whole light setup thing. I bought two six channel receivers with built in two pin light control sockets, the Dumborc P6DCG, but have no idea what light sets it'll support. I also bought an amber emergency light bar for on top of the flatbed, the instructions said to plug it into a servo channel and use that channel to control it but it didn't give any specifics on channel setup involving if it's just a trigger to turn the lights on then they do their own thing or if the light bar acts as a servo would and changes modes by reading proportional control movement, like the steering and throttle do. I do know this though. I plugged it into a servo port on my receiver and it came on, but even though I set up that channel on my MT12 transmitter to just trigger it on or off, it just sits there doing patterns for a few seconds then locks up, and it drains the poor battery that came with the WPL B16 truck I've stripped down as the donor vehicle within five minutes.

If I could figure out what light kit the P6DCG supports I could go ahead and design the cab to fit those lights and print a tail light mount for the rear of the truck.

I also need to find a 1:12th to 1:15th size winch kit to add to the front end of the flatbed.

Still, this is a fun project.View attachment 276651
View attachment 276652

Like you, I am in the dark about lighting set ups.

See what I did there?

I really am curious to see how the lighting and light bar get set up in your truck. Great job getting it this far along!

 

[James A. Doty]

Like you, I am in the dark about lighting set ups.

See what I did there?

I really am curious to see how the lighting and light bar get set up in your truck. Great job getting it this far along!

Thanks. It's been a bit of an up hill struggle, but I think I'm finally seeing the light at the end of the tunnel. Yup, Seeing what you did lit the light bulb over my head.

After three attempts last night I got the rest of the bed lift parts printed last night. Two of the parts are basically cylinders which wouldn't stay stuck to the bed even though I washed the bed with soap and water, cleaned it with isopropyl(sp?) alcohol, used bed glue, and added a brim around the parts, so I printed them vertically and problem solved.

Today I need to design the front bumper mount and tweak then reprint the electronics tray. Then I need to put the lift mechanism together and bind the receiver to my MT12. Once the electronics tray is complete I need to load up the PETG I bought for the cab and print it. The cab will be printed in three different colors and I expect it'll take at least six hours to print. The cab has a flat back so I could print it facing up but I think it would be best to print it angled back at 45 degrees to cut down on support material inside the cab.

 

[HPIguy]

All that wiring would drive me insane. Hats off to you for such a daunting project, it's turning out great!

 

[James A. Doty]

All that wiring would drive me insane. Hats off to you for such a daunting project, it's turning out great!

Once I have it all working I'll have to do some serious wiring management.

Does anyone know of a good winch in the 1:12th scale world I could use?

 

[CertifiedMike]

Once I have it all working I'll have to do some serious wiring management.

Does anyone know of a good winch in the 1:12th scale world I could use?

I'm glad my comments were so enlightening.
Great progress!!!

I think Reefs makes a good winch but not sure how small it is.
Could you use a regular mini servo and print/fab the rollers and winch mechs?

I agree, all that wiring would move me to a whole different department at the mental institution!!!

Good luck!!!

 

[James A. Doty]

I'm glad my comments were so enlightening.
Great progress!!!

I think Reefs makes a good winch but not sure how small it is.
Could you use a regular mini servo and print/fab the rollers and winch mechs?

I agree, all that wiring would move me to a whole different department at the mental institution!!!

Good luck!!!

I think it's possible that I could 3D print a winch of some sort, using a continuous rotation servo like the two I'm planning on using to move the bed forward and backward and to tilt it. I have no experience doing so though. I bed I could make one work though, I was just being lazy.

 

[James A. Doty]

I found out this morning that the pivot arms and associated parts won't work for me, these are parts I got from someone else's stl file on a rollback truck he made that I had to scale up 35%. The lower pivot bar is too short but will be easy to reproduce.

I'll have to redesign the pivot arms to make them no more than 4mm thick and constrain their width to no more than 10mm because the pivot arms I printed won't clear the mount for the twin rear axles.

I have to redesign the pivot nut holder as well so that the cylinders that hold the pivot arms where they articulate in the middle are 8mm long each and that the nut holder box in the middle that the threaded rod needs to pass through is longer from side to side. The overall width of this assembly needs to be 45mm so it fits within the sub chassis I made, the original sub chassis was narrower than the one I designed and I forgot to take that into account.

At this point there's no way I can finish this project by the end of the day tomorrow, but if I don't have too many weekend distractions I should be able to complete it by sometime Monday.

 

[James A. Doty]

My pivot arms to lift the flatbed are too short by 3.207mm. The upper pivot bar is CA glued in place which traps two of the four pivot arms so I can't change them, but I can get the bed tilt mechanism apart to replace the other two pivot arms, so I made a copy of one of the trapped pivot arms, cut it down the middle between the two ends and added 3.207mm to the middle. My current print job just finished, when the bed's cool enough to remove it I'll print the two remodeled pivot arms.

The pivot arms were just short enough that the bed wouldn't lay flat. It was either redesign the sub chassis or redesign the pivot arms. The pivot arms is my easiest choice.

 

[James A. Doty]

I had to redesign my bottom pivot pen bar due to clearance issues and installed them. I ran a test by plugging the pivot servo into channel two on the receiver, instead of the drive motor and using the throttle and brake on my MT12 to operate the continuous turn servo and all worked well until I CA glued a nut on the threaded rod and tried to lower the deck. The stop nut I glued to the threaded rod banged into the mounting plate for the rear suspension. It was hard to get in there but I used my battery powered Dremel to grind a divot for the nut to clear. It helped but it's not perfect. I'm going to have to grind down the corners of the stop nut to fix it. I could try to break the nut free with a stout pair of pliers and a nut driver but I could end up accidentally damaging plastic parts.

Once I verified that the tilt mechanism worked I grabbed my good print of the bed my long threaded rod and a nut to capture under the flatbed and put together the bed slide. I had to grab a servo extension to test things, I'll also have to use that when I organize the cabling, and plugged that into channel two of the receiver in place of the lift servo and gave it a try. The slide works perfect and didn't need any modding of any kind.

I then installed the joystick on my MT12 which I'll program later. I'll use left and right to slide the bed forward and backward, and up and down to tilt the bed up and lay it flat again.

I don't like my servo to threaded rod couplers, too much wabble and the little M2 grub screw by itself couldn't hold the threaded rod in place. So I backed the grub screws out a bit and pulled out the threaded rods and put a dab of CA glue on them then put them back in the threaded rod adapters and re-tightened the grub screws. Man the hex driver for an M2 grub screw is crazy tiny. Also I dropped on of those M2 grub screws on the floor in my kitchen and it will never be seen again.

Here's a video of the pivot servo at work. There's more wobble than I'd like to see, and it's very slow. But it does work and I think it's damned cool.

pivot servo test

I decided to buy four rolls of Bambu Lab PETG-HF to print the cab since it'll be at least a three color print. I did so because the PETG-HF provides a nice mat finish and prints something like 30% faster than their PETG Basic filament. The cab will be either blue or red, I'll decide once the rolls of PETG-HF arrive in a few days.

Up next will be designing the mounting bracket to attach the front bumper to the front of the cab. I'll do a join and make the bumper part of the print, or maybe not It would be nice to be able to replace the front bumper if I damage it. I could design a pair of mounts using self tapping M2 screws to hold two shafts together, an exterior hollow shaft attached to the back of the bumper with an opening to pass the M2 screw through and a solid shaft attached to the cab which will fit inside the inner dimension of the hollow shaft with a hole that lines up with the hole on the bottom of the bumper shaft. Just slide the bumper on and use the screws to hold the bumper on.

I suppose I should make the cab side mounts replaceable but that seems like work and more fasteners.

 

[CertifiedMike]

I had to redesign my bottom pivot pen bar due to clearance issues and installed them. I ran a test by plugging the pivot servo into channel two on the receiver, instead of the drive motor and using the throttle and brake on my MT12 to operate the continuous turn servo and all worked well until I CA glued a nut on the threaded rod and tried to lower the deck. The stop nut I glued to the threaded rod banged into the mounting plate for the rear suspension. It was hard to get in there but I used my battery powered Dremel to grind a divot for the nut to clear. It helped but it's not perfect. I'm going to have to grind down the corners of the stop nut to fix it. I could try to break the nut free with a stout pair of pliers and a nut driver but I could end up accidentally damaging plastic parts.

Once I verified that the tilt mechanism worked I grabbed my good print of the bed my long threaded rod and a nut to capture under the flatbed and put together the bed slide. I had to grab a servo extension to test things, I'll also have to use that when I organize the cabling, and plugged that into channel two of the receiver in place of the lift servo and gave it a try. The slide works perfect and didn't need any modding of any kind.

I then installed the joystick on my MT12 which I'll program later. I'll use left and right to slide the bed forward and backward, and up and down to tilt the bed up and lay it flat again.

I don't like my servo to threaded rod couplers, too much wabble and the little M2 grub screw by itself couldn't hold the threaded rod in place. So I backed the grub screws out a bit and pulled out the threaded rods and put a dab of CA glue on them then put them back in the threaded rod adapters and re-tightened the grub screws. Man the hex driver for an M2 grub screw is crazy tiny. Also I dropped on of those M2 grub screws on the floor in my kitchen and it will never be seen again.

Here's a video of the pivot servo at work. There's more wobble than I'd like to see, and it's very slow. But it does work and I think it's damned cool.

pivot servo test

I decided to buy four rolls of Bambu Lab PETG-HF to print the cab since it'll be at least a three color print. I did so because the PETG-HF provides a nice mat finish and prints something like 30% faster than their PETG Basic filament. The cab will be either blue or red, I'll decide once the rolls of PETG-HF arrive in a few days.

Up next will be designing the mounting bracket to attach the front bumper to the front of the cab. I'll do a join and make the bumper part of the print, or maybe not It would be nice to be able to replace the front bumper if I damage it. I could design a pair of mounts using self tapping M2 screws to hold two shafts together, an exterior hollow shaft attached to the back of the bumper with an opening to pass the M2 screw through and a solid shaft attached to the cab which will fit inside the inner dimension of the hollow shaft with a hole that lines up with the hole on the bottom of the bumper shaft. Just slide the bumper on and use the screws to hold the bumper on.

I suppose I should make the cab side mounts replaceable but that seems like work and more fasteners.

Grub screws and eclips... Somewhere in my house, theres about 30 or 40 of each all neatly stacked in a corner waiting for me to find them.