[WIP] Yet Another Baja / Trophy Truck

[miguev]

Hello!

I’m not particularly proud of this Technic horror I’ve created, but I’d like to share it with you rather than keep it to myself, possibly forever.

Shortly after I learned about (and supported) SBrick and MiniZip in KickStarter, I started dreaming of building powerful, compact MOCs using a new combo: PP3 NiMh battery + MiniZip + SBrick + 5292 RC Buggy Motor.

This is my first attempt at it, now that Android SBrick app (1.3+) is finally usable

Functions

• Drive: 2x 5292 RC Buggy Motor, each connected to a separate SBrick, each powered by a separate PP3 NiMh 250 mAh battery using MiniZip.
  
• Steering: PF Servo.
  
• Front suspension: independent, soft, long travel, with “fake” positive caster
  
• Rear suspension: solid axle, dragged (didn’t figure out how to do four-link)
  
• 4x Lego LED
  

Still haven’t applied myself to learning proper bodywork, so designing my own was out of the question. I went for an easy, fairly plain one. No openable doors, bonnet or anything. I worked with these two photos and scaled for 62.4mm tires.

Full size (> 1024px): 1, 2.

Photos were made really quick, during a baby siesta (indoor) and in short incursions (outdoors) no more than 20 meters from home. For now, I can only dream of having more time and freedom for this :D

v0.99 without stickers:

v1.0 with stickers based on

video:

Old school navigator refused to deal with GPS and computers, wanted just a compass (70001pb02) and a map with an X that marks the spot. Smart dude, run off with the loot.

Very short of creativity and sleep, the only alternative I could think of to get rid of the demonic Monster logo and brand was a rather lame one: Music Energy. Example diff:

I asked friends to vote in G+ and 3 out of 4 prefer Music, but the one who prefers Monster is my the only one into LEGO. I’m divided, will probably print them and try them on, but still not sure which ones to use for filming.

I started with 1 battery, 1 SBrick, 2 motors. It seemed to run well. Adding an extra battery and Sbrick seems to make it run even stronger / faster, although SBrick developer Zsolt Majoros said it shouldn’t matter. The real reason I added the extra SBrick is that “2 ports 1 function” only works in Android app when those 2 ports are on separate SBricks.

You may ask why use PP3 batteries instead of the acclaimed LiPo batteries… mainly because they are expensive, and a bit of a lottery with their thermal protection. MiniZip + PP3 NiMh 250 mAh wasn’t a whole lot cheaper, but the combo is certainly more compact, half the weight and doesn’t have any thermal protection. SBricks can draw as much current as the motors want, with just a small risk of overheating and possibly catching on fire… ah well, what could possibly go wrong?

I haven’t actually managed to make the batteries warm up, they get warmer when charging. One likely reason for not achieving hotness is short life, according to this battery life calculator, they’d last 3.5 minutes at 3 A, 10 minutes at 1 A, 20 minutes at 500 mA. Can someone make a better-informed / estimation of a more realistic battery life?

But there are more and worse problems, for which I sure can do with your advice!

Caster angle is fake, isn’t? I mean, I just shifted the upper A arms a half stud backwards, but both A arms still move vertically. I think this is why big bumps will throw the truck’s front up rather than only the front wheel/s going up.

When hitting a big bump with a front wheel, the wheel will thrust up and with it the whole car will roll to the opposite side. This results in a raised rear wheel taking all torque to just spin in the air, so the car stops until the raised wheel hits the ground again.

Shifting the upper A arms a half stud backwards messed with the steering geometry, so now there’s a not-so-slight bump steering. I think this, combined with the twisting effect on the solid axle, is what’s causing the truck to steer to the left when accelerating. Too bad.

Motors are hard coupled on their fast output and then geared down 20:12 twice, not including the 20-tooth to differential connection. Maybe I could / should gear down 20:12 only once, haven’t had a chance to try yet.

I suppose integrating the motors in the rear axle and connecting wheels directly to them would help with the last couple of problems, but couldn’t figure out how to fit that in this body just yet. I’m also concerned that if one battery drains faster, the motor (no longer) powered by it will get damaged. With each rear wheel directly on one motor, that would result in the truck going in circles, but motors wouldn’t get damaged. How bad is this?

Steering with SBrick (v1.3) as a significant latency, in the time it takes from the moment I slide my finger to a side (much or little) to the moment when the PF Servo starts moving, the truck is already going the wrong way. It’s really hard to drive straight.

rm8, what’s your experience regarding this latency with your Double Trouble?

If anyone has not seen rm8’s Double Trouble, I’ll put it as “my dream, properly done”

Thank you for reading. If you were looking for a video...

EDIT(25.05.2015): slightly better pics.

EDIT(26.09.2015):

I’m now a little more proud of my creation, at least the suspension seems right to me: it’s long travel and soft enough to reacts promptly to bumps, but the car doesn’t sink too much on it. I dare say it works better than most others, probably because it’s much harder to this the a bigger scale most others have been working with.

The car is still not really fast, so I didn’t bother measuring its speed. I did try putting less reduction in the drivetrain, but that only resulted in lower speed due to lower torque, so I reverted back to my original setup. It’s still fast enough to be impossible to drive well, specially with the terrible latency in the SBrick. Latency is not a problem with the port tester, so it doesn’t look like a hardware limitation. Anyway, it’s fast enough to be fun.

Thanks to Sir Wolf’s help and support, we finally have a somewhat decent video. Enjoy! :)

And we learned many things the hard way: by failing.

Fake caster angle is not good, you need real caster for off-road racing. I took the idea from someone’s supercar project here (sorry, couldn’t find it again) to displace the upper suspension arm by ½ stud backwards from the lower arm (see belly shot above). That gives you quite a bit of caster angle on the wheel (or snowmobile skies) but it does not help reacting promptly to the most serious bumps. It also screws the geometry in that the gear rack should ideally be ¼ stud backwards, but it’s either 0, ½ or 1. This results in notorious bump steering: front wheels are toes out when suspension is fully extended, and toes in when fully compressed. When this adds to the torsion exerted by the powerful motors on the live axle (see in the video how left front wheel jumps up when car starts). All in all: bad Idea.

Portal hubs from 8070 are not good for off-road racing, I should have used the ones from the snowmobile 42021 (2015). They are also too expensive to go on dirt with them, so I didn’t.

Differential slows down or even stops the car when one rear wheel take off. I knew this was a problem with crawlers, but never imagined how bad it’d be on a trophy truck. Damn it, I’ll never do this again. Just use one motor per wheel, and accept that if one motor runs out of battery or losses signal, you might take a sharp turn or find yourself driving in circles for a little, depending how the front wheels cope with the imbalance.

MiniZip are great to get “buggy-motor-grade” power in a smaller size than LiPo batteries. PPA 9V batteries can fit a width of 3 studs, so a 5x11 panel makes for a perfect home. However, MiniZip’s lack of power switch in makes it a complete hassle to replace batteries. Should keep them very easily accessible.

Edited September 27, 2015 by miguev

[MajklSpajkl]

Miguev, dude, why again shouldn't you show this to us??? I think it is a very good build! So lift your spirits a bit higher man. I'm not sure about "fakeness" of your caster angle. As far as my understanding of caster angle goes, it has nothing to do with suspension arms, but only with the inclination of the line between upper and lower pivot point...

Looking forward to your video!!!

Edited May 21, 2015 by MajklSpajkl

[rm8]

Hi very nice and detiled truck!

I thing using trans clear plates 1x2 as front light will be closer to original car.

To di a best working caster angle - just attach subframe with front suspension with angle to the main frame, like Madoca do it in his last buggy, for example. As for steering - yes steering with Sbrick at high speeds is not easy because of 1)latency 2)no feedback at hands. Hand are always out of slider/button. You can try do control with buttons instead of sliders: just 2 big buttons left an right without precise steering. So I solved steering problem other way: just drive at large space locations:)

Edited May 21, 2015 by rm8

[darksheep]

Very cool love the GPS(Map) on the dashboard .

Nice to see its to about the scale for the Technic figure

[Graydingo]

Totally awesome. I love baja trucks. The stickers add nice detail.

[Rishab N]

Not sure why you wouldn't wanna share this man. It looks great

[miguev]

Thank you so much for your kind comments!

I've been rather frustrated by my filming attempts. The truck looks decent, but drives terribly, it drives me mad! I don't have large scale locations near home, and so far don't see a chance to go anywhere with it. It's so hard to drive I can't even film what I want by placing the camera on the ground and driving near it, the truck always goes in a random trajectory quite different than intended. I may have better luck taking the truck to work and asking colleagues to drive it while I chase it with the camera

I have a question for those of you who have the full

as well as the SBrick, and have tried driving fast vehicles with both: should I just buy a full RC set (8376, 8475, 8366) for better driving experience? (re. steering latency).

[PKW]

Thank you so much for your kind comments!

I've been rather frustrated by my filming attempts. The truck looks decent, but drives terribly, it drives me mad! I don't have large scale locations near home, and so far don't see a chance to go anywhere with it. It's so hard to drive I can't even film what I want by placing the camera on the ground and driving near it, the truck always goes in a random trajectory quite different than intended. I may have better luck taking the truck to work and asking colleagues to drive it while I chase it with the camera

I have a question for those of you who have the full

as well as the SBrick, and have tried driving fast vehicles with both: should I just buy a full RC set (8376, 8475, 8366) for better driving experience? (re. steering latency).

this is what i can say :

the latency of the Rc system is not worse than the one of the PF one, it is only that the first stage control of the 3 degree is more or less at 20% lever travel ;) the output still being fast as a servo motor; about you truck you should remove the caster angle and reinforce the suspension using the same piece used n the snowmobile to reinforce steering, I don't have an sbrick but I think that with some practice you can drive it also with the delay I usually drive faster veichle (the same output not geared 1.6:1 twice but with the differential) and with lego remote is not difficult.

one question :3 those batteries has a total of 500ma/h and so the only point it that you have a lighter veichle, shmade with 2 v1 receiver drove 2 rc motors connected to 56x26 wheel at the faster output, why yu don't try to make it of pure lego? maybe it could work better ;)

PS: if your truck is horrible, what is mine?

[flyboy01]

nice truck

[miguev]

this is what i can say :

the latency of the Rc system is not worse than the one of the PF one, it is only that the first stage control of the 3 degree is more or less at 20% lever travel ;) the output still being fast as a servo motor; about you truck you should remove the caster angle and reinforce the suspension using the same piece used n the snowmobile to reinforce steering, I don't have an sbrick but I think that with some practice you can drive it also with the delay I usually drive faster veichle (the same output not geared 1.6:1 twice but with the differential) and with lego remote is not difficult.

Yeah, I think the 3 stages of the RC system, plus the fact that you can feel the lever in our finger/s, help a lot.

Why remove the caster angle entirely? I already have a reinforcement here, it's a thin 5L liftarm betwen the A arms, look for the red 2L axles in the arms. It's weird, but it works.

one question :3 those batteries has a total of 500ma/h and so the only point it that you have a lighter veichle, shmade with 2 v1 receiver drove 2 rc motors connected to 56x26 wheel at the faster output, why yu don't try to make it of pure lego? maybe it could work better ;)

Yes, batteries being lighter and smaller are one of the reasons to use them, it allowed me to build 2 seats in this truck, both suitable for Technic minifigs. It wasn't like I needed that, sure I could have filled the cabin with 2 lipos, but as I noted they're expensive and may shut down under stress.

There are also 600 mAh batteries, but I've read too many horror stories of such batteries being fakes: they're labeled as 600 mAh but in fact are 200 mAh. Besides, I couldn't find them anywhere where I live.

PS: if your truck is horrible, what is mine?

A green apple from 2115!

[PKW]

Yeah, I think the 3 stages of the RC system, plus the fact that you can feel the lever in our finger/s, help a lot.

Why remove the caster angle entirely? I already have a reinforcement here, it's a thin 5L liftarm betwen the A arms, look for the red 2L axles in the arms. It's weird, but it works.

Yes, batteries being lighter and smaller are one of the reasons to use them, it allowed me to build 2 seats in this truck, both suitable for Technic minifigs. It wasn't like I needed that, sure I could have filled the cabin with 2 lipos, but as I noted they're expensive and may shut down under stress.

A green apple from 2115!

it is weird but it makes the car steering while it hurt obstacles and it is less useful due ti the light chassis, that steering seems to have too many play ;)

you should Try with normal lego BB to understand of it is only a problem due to sbrick control xD

these RC motors are wasted with a 3.1 reduction so maybe you can use L motors to gain same speed but test it with the lego bb

mine green apple is faster, stronger and drive better than your beautiful truck ihihih there is a reason for my horrible aesthetics

[sm1995]

A technic horror?! what?! I think it's absolutely awesome. The only thing I don't like about it are the slightly awkward looking A pillars. I think that replacing them with steering links would look better.

Other than that, it looks superb.

Edited May 22, 2015 by sm1995

[miguev]

Yeah, the A pillars spoil the whole thing. I'm still trying to do better but can't find a way with steering links, they're too short or too long, and all my flex axles are too long. Besides, I do want the roof to be really sturdy, the whole truck is stored upside down on its roof, to avoid compressing shocks for a long time.

I just tried removing one of the 20:12 with a 16:16 so there is not that much reduction any more... it's scary! Even the slowest it can drive is a bit too fast for the steering latency, plus the climbing power it had seems to be gone (indoor test only so far). Still, I think I'll leave like this if it can still drive through bumps, it'll be even harder to drive and film but if I do manage to film something it's gonna look more impressive. Thanks for the suggestion

[Zerobricks]

Its looks really great, the stickers sure add a lot. About gearing, I suggest you to use the gearing which still alows the truck to go uphill, yet is fast enough. Also using silicone spray on gears and axles will help.

[miguev]

I had never heard of silicon spray until you used it for your Mercedes C... would this one work?

[Doc_Brown]

This is a really sweet truck, you should be proud! Amazing photos as well, with great stickers!

Looking forward to the video.

[miguev]

Thank you for one more nice comment, appreciate it!

I find it hard to feel proud of my work when I start looking at the works ( of others, specially in this case since rm8 and Sariel are doing the same! Anyway, I won't drop the project, I posted a teaser and now I own it to you all.

Video will take some weeks at least, I think. Filming near home is just impossible, so I'll take the truck to work and try to film it during lunch break with help from the 2nd SBrick's owner, so he'll have some fan too.

Meanwhile, I might be able to put together another teaser trailer with what I've filmed at home so far.

[DamonMM2000]

Heh, I think Sariel also built a replica of the same vehicle you based your MOC off of…

Both are quite nice, to be honest!

Edited June 11, 2015 by DamonMM2000

[miguev]

Yes, and so did rm8 (Double Trouble). Needless to say, I didn't aspire to be at their level, this is only my 2nd finished MOC

[MaxSupercars]

Miguev I like your Rally car... With stickers looks better than Sariel's... The car from rm8 is also classy... I like your front lights... nice detail...

MaxSupercars

Edited June 11, 2015 by MaxSupercars

[miguev]

Thanks Max, I just did something you (and others) may like: please

(it looks terrible embedded).

I reckon this won't live up to the expectations, but I'm afraid I don't have better footage just yet, it'll take me at least a few more weeks for that.

The whole point of this truck is the soft suspension, with plenty of travel and body roll, I hope that can be appreciated in the video.

Any comments about my video editing skills (ahem) will be much appreciated, please leave them there in YouTube or PM me.

[MaxSupercars]

Nice video... I like to look at working suspension... :) Where did you lost stickers? :)

Max...

Edited June 20, 2015 by MaxSupercars

[miguev]

This was prototype #1, before I even thought of stickers.

[__________________________]

Are there more pictures? Would like to make an LXF for the chassis. :thumbup:

[miguev]

Yes, actually, here. I don't think the chassis will be very exciting, but I'll try make a "Jedi Build" video of it later this year. I was hoping to film it better this or next week, but with a red alert for heat wave and me no liking hot air at all, will have to postpone quite a bit. Once I'm done with the filming, I'll take it a part and record that. So it'll be at least a couple of months