[MOD] Eric Trax's Scorpion 756 mods + SBrick Pro beta vs BrickController2

[pdw]

@eric trax's brilliant CLAAS Scorpion 756 telehandler MOC is the first Lego model that's really inspired me in a long time.  I found the combination of clean, scale looks and a genuinely "playable" but compact RC model very appealing.

My original plan was to build the model and stick a few lights on it, but it transformed into a bit of a project for me.  This has turned into quite a long post, so I've hidden some of the details in spoilers.

The original model has four wheel steering, but the CLAAS telehandlers have four steering modes: two wheel, four wheel, crab and "offset", and I found myself wondering if this could be reproduced in the model.  This meant squeezing another servo and more wiring into an already tight model.

I originally built the model with two SBricks rather than three IR receivers, which bought me a little bit of space in the cab. The bevel gears do introduce some additional play into the front steering but it's not normally too obvious. The next challenge was how to make the steering controllable in the way that I wanted, which lead me on a bit of a software development journey.  More on that below.

The other significant mod is the mudguards.  At first I concluded that there simply wasn't space, but after a lot of attempts I struck upon something that works, and that I'm happy with.

I had to redesign the rear lights in order to get more clearance (I think the result is actually a bit closer in style to the real thing) and the front of the cab and exhaust position also needed tweaking for more clearance.

Lights

Two SBricks for six functions meant two spare channels, which I filled up with lights:

• Six front lights
• Two rear lights
• Front and rear left and right turn signals
• Rotating beacon light

I tried hard to keep the wiring as discrete as possible, but I must own up to drilling through a hollow stud for the beacon wiring.

Spoiler

The wiring ended up being fully custom, using some Light My Bricks components.  I wanted the lights to be remotely controllable and dimmable, which the standard LMB PF connector doesn't allow, as it connects to the permanent PF lines and uses a 5V regulator. 

The LEDs are 0805 SMDs, which are just small enough to fit in the hollow on the back of a stud, and can be fed through just about any Lego hole you can find (e.g. the gaps in hinge joints).  You can buy them pre-wired, but I ended up soldering my own as it's much cheaper and allowed me get exactly the right length and use all black wiring which looks tidier.

The various orange LEDs I tried were disappointing, but I found that warm white through a trans orange tile works well for the turn signals.  Tail lights are red LEDs through trans red tiles, and other lights are normal white.

The wires are spliced onto LMB connectors with suitable resistors to run from 9V.  The beacon light is from LMB, and needs 5V so that's on a 5V regulator and diode bridge so that it's on whenever the output is on.  The main lights are on the same channel, but only come on in one polarity.  Likewise, the turn signals are wired onto a single channel, but with opposite polarity for the two
directions.

Seeing as I was already committed to butchering PF extension cables to make LMB adapters, I decided it was reasonable to also butcher the PF extension cable that drives the fork tilt motor, so that the unused "permanent" lines are used to power the lights on the arm, avoiding the need to run another set of wires from the arm.

 

Other mods

I made a few other "functional" mods which may be of interest to others building this model:

• Slope bricks on the front chassis:

Spoiler

The arm is a tight fit in the chassis, and I found that occasionally it doesn't come down quite straight and the LA mount catches on the side of the chassis.  The slope bricks on either side of the chassis fix this.  I also prefer this aesthetically as they fill the gap when the arm is fully lowered.

• Spacers rather than axle joiners on the arm extension driveshaft, to remove the risk of the tilt motor cable getting sucked through the hole in the top of the arm.  The spacers rotate freely, avoiding the cable getting snagged.  
• Extra half bushes in the lower LA joint to fill the gaps and prevent cables getting caught in the gears.

I slightly redesigned Eric's neat system for quickly changeable attachments so that I could use the bucket on the same system.  The change was necessary in order to get enough clearance for the full range of bucket tilt.  It's a step back aesthetically, but it's worth it for me for the ease of swapping.

Controlling the model

As mentioned above, the Scorpion has four steering modes.  Rather than just putting the two servos on separate controls, I wanted to try and emulate these modes: 2WS, 4WS, crab, and offset mode which allows the position of the back axle to be set, and then the vehicle steered using the front axle whilst crabbing.

SBrick Pro Beta

In order to implement this, I started looking at the SBrick Pro Beta app.  This uses visual programming to allow you to do just about anything with different controls.  I got quite a long way down this path, including things like differentiating long and short button presses on a gamepad, emulating a self-levelling fork by blipping the tilt motor when the elevation motor is running, various steering mode switches, and a "drive mode" switch to temporarily put the accelerator and steering on separate joysticks for better control.

I even implemented a system that ramped up steering sensitivity as you increased the crab offset so that you could have the model crab forwards with the joystick centered, but still reach full lock in both directions.

Unfortunately, and as you'd expect from a beta, it's still quite rough around the edges, and whilst it makes doing complicated things possible, it makes doing simple things quite hard.  One issue is that are no events for joystick input, so you have to run a tight loop to constantly poll their position.  I think as a result of this, the app is absolute power bandit.

Overall, it's a great app with a lot of potential, and I'm really looking forward to future releases.

I found that the drive on the model was a little underpowered, particularly when turning, which I think is down to friction in the CV joints.  The model was also getting enough play that swapping and charging AAA batteries was getting boring.  The new SBrick app supports lots of other devices, including BuWizz.  BuWizz on its own isn't ideal for this model as it doesn't have enough channels, and it'd be a struggle to fit two of them, but the combination of BuWizz + SBrick seems like a real winner: 8 channels in less space than a AAA box + one IR receiver.

Thanks to some great service and very fast delivery from BuWizz, I was able to get a BuWizz out of the EU before the UK, so I swapped the battery for a BuWizz.

Spoiler

Eric's model has a very neat button hidden in the top of the engine housing.  I adapted this to work with the BuWizz.  It can be removed to allow charging with the housing in place, and a trans black tile, clear boat stud and another drilled hollow stud allow the status LED to be just visible when it's in place.

Unfortunately, I immediately hit a problem: the BuWizz only turns on power to the permanent lines of its outputs once it's connected over Bluetooth, which means that if you power an SBrick from a BuWizz, you must connect to the BuWizz first.  The SBrick beta app doesn't do this, and it's close to impossible to get it to connect to all devices at once so I found myself looking at BrickController2.

BrickController2

BC2 has the same problem, but it can be tricked into finding the SBricks by running the BuWizz app in the background.  Even once you've discovered the SBricks, reconnecting was a bit hit and miss.  Fortunately, BC2 is open source, and I managed to fix this myself (hopefully this will be in the next release).

BrickController2 is a great app.  It's fast, reliable and easy to configure, but didn't allow me to implement the different steering modes I wanted.  The joy of open source (and a good few hours of coding) mean that I now have a custom BC2 app with a flexible system of "modes" that can be set or toggled using controller buttons.  This allows me to switch between 2WS and 4WS, and crab and normal.  I can also press and hold a button to set the rear axle position for offset mode, and the position "sticks" when the button is released.

I intend to submit this feature in due course, but the code needs a bit more work first, and I'm happy to have been able to contribute a handful of other minor bug fixes and features to BC2 along the way.

Still to do

The one unresolved issue I want to address is trying to make the fork tilt more controllable as it seems very hard to control the speed of the motor.  Set at 100% power, the fork moves far too fast to be controllable when unloaded, but set at anything less than 100% and it often doesn't have enough power to move at all when loaded.

I also want to try BuWizz's ludicrous mode for drive, but need to add a cable with a voltage drop diode to protect the SBricks.

Once again kudos to Eric for this model, and also to @M_longer for the very high quality instructions.  I see instructions for some new attachments have just been released, so that may be what I'm doing next!

More photos on Bricksafe. I'll try to do a video showing the different steering modes.

[deraven]

I really don't have time to comment on this properly, but I did want to at least say:  This looks wonderful, aesthetically. Very nice combination of technic and system elements to get the look right.  Also a great set of features and controllability worked in, even if there are some bits that need refinement or fixes as you noted.  Fantastic build!  

[1gor]

Since I (try to) work on my telehandler for a while, I have noticed some amount if slack when I add gears to servo and with time tires are not aligned anymore. IMHO the only way is to implement one servo directly per axle, but for that you need more space / bigger model...

[pdw]

Quote

 I have noticed some amount if slack when I add gears to servo and with time tires are not aligned anymore

The slack is only really noticeable because it's 4 wheel steer, and you can sometimes see the front wheels turned a slightly different amount to the rear wheels.  I reduced it a bit by bracing the cross axle as much as possible. Quite a lot of the remaining play is due to the very short axle in second servo.  As you say, I don't think there's any alternative at this scale.

[pdw]

I started fiddling with the bracing for the arm extension worm gear, as with too much load on the fork the driveshaft will bow upwards and the worm gear will slip.  As part of doing this I realised that it was fairly straightforward to increase the extension of the arm to get an extra 4 studs of usable reach.

.

Lift height is now 41cm which is bang on scale - 7m at 1:17.

I've also had some success with making the fork tilt more controllable by dropping the PWM frequency on the SBrick controlling the tilt motor.  This seems to give much more torque at lower speeds.

[eric trax]

On 1/12/2021 at 1:38 AM, pdw said:

is the first Lego model that's really inspired me in a long time.  I found the combination of clean, scale looks and a genuinely "playable" but compact RC model very appealing.

It's it very pleasant to see my model inspire someone to make  improvements. You did everything that limited me when I was designing the telehandler. The limitations resulted from the fact that I wanted to optimize the partlist and make little bit easy a very hard building process.

On 1/12/2021 at 1:38 AM, pdw said:

originally built the model with two SBricks rather than three IR receivers, which bought me a little bit of space in the cab.

My copy has 2x sbrick. I installed them almost immediately after completing the base version. They were not included in the building instructions due to the lower cost of the models. This configuration offers great opportunities and possibility to control model with PS4 pad.

On 1/12/2021 at 1:38 AM, pdw said:

Two SBricks for six functions meant two spare channels, which I filled up with lights:

On 1/12/2021 at 1:38 AM, pdw said:

The other significant mod is the mudguards.  At first I concluded that there simply wasn't space, but after a lot of attempts I struck upon something that works, and that I'm happy with

My lights for the scorpion have been waiting for installation almost half a year. I can't find time for this. Your fenders look great. I doubted that they could be successfully built. Congratulations.

On 1/12/2021 at 1:38 AM, pdw said:

I slightly redesigned Eric's neat system for quickly changeable attachments so that I could use the bucket on the same system.  The change was necessary in order to get enough clearance for the full range of bucket tilt.  It's a step back aesthetically, but it's worth it for me for the ease of swapping.

An interesting change. When designing, I decided that the appearance was more important to me. Attaching the bucket to the frame extends the model and one stud. The bucket mounted directly to the arm is already quite far from the front axle. Your idea makes it very easy to replace attachments.

On 1/12/2021 at 1:38 AM, pdw said:

Unfortunately, I immediately hit a problem: the BuWizz only turns on power to the permanent lines of its outputs once it's connected over Bluetooth, which means that if you power an SBrick from a BuWizz, you must connect to the BuWizz first.  The SBrick beta app doesn't do this, and it's close to impossible to get it to connect to all devices at once so I found myself looking at BrickController2.

 

On 1/12/2021 at 1:38 AM, pdw said:

The model was also getting enough play that swapping and charging AAA batteries was getting boring. 

Buwizz saves even more space in the cab. I decided that it will not be necessary in my model. This causes a problem with the sbrick power supply. I use a rechargeable lego 8878 battery. When the model is working, the next battery is already charging. The exchange takes 30 seconds and the model can continue to run. At the last exhibition, where we presented the first version of the technic mockup Scorpion worked for 16 hours with short breaks. During this time, I changed the battery 4 times. I smeared all axles with Teflon grease. This avoids bricks damage. The model is very effective. The fact that it has been running for so many hours without a breakdown is very important to me. Hours devoted to designing were not wasted.

On 1/12/2021 at 1:38 AM, pdw said:

BrickController2 is a great app.  It's fast, reliable and easy to configure, but didn't allow me to implement the different steering modes I wanted.

I use this application to control all my models. It is great and offers many possibilities. For me, the most important thing is that I can use two buttons to control the engine in two modes. Or activate two functions with one button. Driving, steering, lifting and tilt control is very difficult. So, when using the trigger, I have programmed: forward driving (85%) and lifting (100%). Then I can pay attention to tilt and steering. It's not a problem for me.

You wrote that you have a tilt problem. I use toggle buttons and set the correct position with quick clicks. It takes practice, but is quite convenient.

On 1/23/2021 at 8:33 PM, pdw said:

I started fiddling with the bracing for the arm extension worm gear, as with too much load on the fork the driveshaft will bow upwards and the worm gear will slip.  As part of doing this I realised that it was fairly straightforward to increase the extension of the arm to get an extra 4 studs of usable reach.

I am aware of this disadvantage. Your improvement looks interesting. Can you take a picture of the arm without the side cover?

 

The huge work you put into changing your model is a big compliment to me. I am glad that my work is so motivating for someone.

[1gor]

I see that I'm not the oy one using screwdriver with my MOCs during development (specially when one IR receiver stopped working ; and completely new one from two weeks ago bought 42095 set)... Nice to see that original mastermind is happy with improvements of his own work 

[pdw]

Thank you very much for the positive comments.  It is very hard to improve anything in this model - pretty much all my changes come with some compromise, so I understand the decisions you made to keep the design buildable, reliable and affordable.

I've actually just spent a few more happy hours modifying.  The play in the front steering from the bevel gears was annoying me so I decided to try something which I'd previously declared impossible:

 

This arrangement is much better than my previous effort.  As well as getting rid of the play, it gets rid of the unsightly servo below the cab.  I was concerned that removing the beams between the drive motor and servo would make the chassis too flexible, but the end result is actually very strong.

The only issue is losing the T pieces that brace the steering axles which means the gears slip if the servos force the steering against the stops.  Not an issue for use with SBrick/BuWizz as you can simply limit the servo travel electronically, but would be a problem for bang bang steering.  I had an "aha" moment when I realised why that bracing was needed.

On 1/30/2021 at 6:22 PM, eric trax said:

My copy has 2x sbrick. I installed them almost immediately after completing the base version. They were not included in the building instructions due to the lower cost of the models.

Getting 3 IR receivers in the cab is very impressive in itself!  I've got one of my SBricks in the "upper" position, and one in the middle at the bottom.  Now that I have the BuWizz, I could get rid of one of them altogether. 

 

On 1/30/2021 at 6:22 PM, eric trax said:

Your fenders look great. I doubted that they could be successfully built. Congratulations.

Thank you.  Sadly, I've discovered a bit of a problem with them which is that at full lock and full speed, the play in the hubs allows the tyres to move really quite a lot and they rub enough to be a problem :-(  I think it's the lack of Ackerman geometry that puts quite a lot of sideways force on the tyre as there's no rubbing on full-lock crab steering, only on four wheel steer. I'll carry on experimenting, but I'm running out of ideas.

On 1/30/2021 at 6:22 PM, eric trax said:

When designing, I decided that the appearance was more important to me. Attaching the bucket to the frame extends the model and one stud. The bucket mounted directly to the arm is already quite far from the front axle. Your idea makes it very easy to replace attachments.

I had the same dilemma, it's actually 2 studs forwards.  For me, practicality won out.  The fact that I have impatient children may be a factor in this :-)

On 1/30/2021 at 6:22 PM, eric trax said:

The model is very effective. The fact that it has been running for so many hours without a breakdown is very important to me. Hours devoted to designing were not wasted.

Agreed!  The reliability has been very impressive.  The one question I did have is the use of the half bevel gear to drive the front diff.  Is there a reason for this?  My model eventually spat out the gear and I replaced it with a full 20T gear.  In the rear, there's a stopped axle so it's fine.

 

On 1/30/2021 at 6:22 PM, eric trax said:

I use this application to control all my models. It is great and offers many possibilities. For me, the most important thing is that I can use two buttons to control the engine in two modes. Or activate two functions with one button. Driving, steering, lifting and tilt control is very difficult. So, when using the trigger, I have programmed: forward driving (85%) and lifting (100%). Then I can pay attention to tilt and steering. It's not a problem for me.

Interesting.  You may be interested in some of the mods I've made for controller modes.  For example, with the increased speed of the BuWizz, I have a button that toggles a "slow speed" mode which halves the drive speed, but there's lots more options for changing what controls do on the fly.

 

On 1/30/2021 at 6:22 PM, eric trax said:

You wrote that you have a tilt problem. I use toggle buttons and set the correct position with quick clicks. It takes practice, but is quite convenient

The problem I had was when using the fork rather than the bucket.  In order to get the fork tip under a palette accurately needs a very tiny movement.  I have it set up on the "hat" on my controller, and use quick taps to get small movements, but even that is too much.  So I reduced the power that the tap uses to slow it down, but then when you put a load on the fork it hasn't got enough power to consistently lift the fork.  I've discovered that lowering the PWM frequency on the SBrick increases the torque so I can now run the motor slowly with a wider range of loads.

There's one more thing I want to try which is that the SBrick has the ability to drive a motor for a specified amount of time.  This should allow you to get short "blips" of drive more consistently, as it's not subject to Bluetooth jitter.  The shortest period is 0.2s which I fear may be too long.

On 1/30/2021 at 6:22 PM, eric trax said:

I am aware of this disadvantage. Your improvement looks interesting. Can you take a picture of the arm without the side cover?

 

 

As you can see, there's nothing holding the 4x2 beam except the side panel, and the 13L beam is only held by a single full pin at the rear.  I was doubtful about relying so much on the plates for structure, but it's proven completely reliable and very stiff.  

Another tiny mod is just visible on the grey pin on the arm just in front of the light is a small elastic band holding the motor cable to the underside of the beam.  This solves the problem of the cable not feeding into the arm correctly which is more of an issue with the extended reach.

 

 

 

Edited February 1, 2021 by pdw
Replaced first photo

[lenzie]

It's been good to read this thread and to see this MOC built with official Lego parts.

I recently built CaDa's version of this MOC, which was endorsed by Eric / released in collaboration with him.

I can say that the quality of CaDa's parts is not on par with Lego parts so the end result of the CaDa kit feels slightly sub-par (to me).  But it was a good build, the end model is highly functional and I enjoyed the experience of trying out a 'non-Lego' product for the first time.

I've published a video about the model that you can watch if you like:

Photos of my finished model are available here: