Speedy's "Bump Steer" Lunch Box Build Thread

[TA-Mark 196]

no small springs to break

If you have broken the small springs, then you fitted them wrong.

The spring coil must be loose on the screw. An overtightened screw will pinch the coil and prevent the coil from working and shift the entire load to just the bit sticking out. Result is the bit sticking out snaps.

The easiset solution to preventing overtightening the screws is to add a brass tube.

I've been thumping very hard on mine for almost 4 years and have still not broken the set supplied in the kit. 5700Kv Mamba, standing backflips, amounts of thumping on them.

[speedy_w_beans 4286]

Nice smoke unit. I never thought to use an old hair dryer for parts, I even have a couple broken down in my "useful parts" box. Are you going to run a fan with it to get the snorting effect? I'd love to see a video of it running speedy

Thanks. I'll try to post a video of the smoke unit after I get the air source sorted out. I bought a battery-powered aquarium pump for $10 to experiment with. Inside is a small motor with a cam and diaphragm pump. I could run the motor on/off to turn the air flow on and off, but it's not a very nuanced breathing effect that way. I've been thinking about driving the diaphragm directly with a servo and using a transmitter stick to control the "exhale" directly, but I'm not sure if it will generate enough air per stroke. I'll give that a shot too. I also have a few air cylinders on order from HobbyKing that have about 20mm of stroke. I'm thinking I could drive one of those with a servo and use a pair of aquarium check valves to make a rudimentary pump. So, I have at least three ideas to try to get the effect I'm after.

HobbyKing air cylinder:

http://www.hobbyking.com/hobbyking/store/__8351__Air_Actuator_20mm.html

Looking good!

I like the touch from the wheels, it definitely adds to the look. Very unique and cool!

Thanks, guys!

If you have broken the small springs, then you fitted them wrong.

The spring coil must be loose on the screw. An overtightened screw will pinch the coil and prevent the coil from working and shift the entire load to just the bit sticking out. Result is the bit sticking out snaps.

The easiset solution to preventing overtightening the screws is to add a brass tube.

I've been thumping very hard on mine for almost 4 years and have still not broken the set supplied in the kit. 5700Kv Mamba, standing backflips, amounts of thumping on them.

As you point out, I probably did tighten down the screws too much in the past. There's nothing in the instructions to say these should be loose or free to rotate; the instructions just provide a final position for the springs and suggest installing the screws all the way. Tamiya could have fool-proofed this by providing the brass tubing you suggest. Anyhow, locking the rod in position works well enough for me. If I didn't do that I would pursue the fifth shock mod instead. The little springs left a bad taste in my mouth.

By the way, did you notice there is another set of holes in the Lunch Box chassis that will accept the front suspension arms? If you leave the battery tray and front suspension mount off the chassis, there is another pair of holes and another pair of channels that will accept the front suspension arms. Cross-referencing the chassis to other Tamiya models, all I see are Lunch Box, Midnight Pumpkin, Montero Wheelie, and Unimog Wheelie models using it. These are all "Big Wheel" models, but I'm wondering what could be done with the chassis using these alternate holes and some short buggy dampers or touring car dampers. I wonder what Tamiya had in mind when they designed this part?

Thanks to all for the comments and thoughts!

[TA-Mark 196]

The original 58044 Pajero used this chassis tub without the battery holder and extensions. Basically a Hornet setup using this tub instead.

[speedy_w_beans 4286]

I looked through the Pajero manual on our main site, and it explains why there are all these leftover parts from the "A" parts tree. The reason why I didn't see the Pajero earlier is because Tamiya USA's site did not have the kit and parts listing for it. Sometimes I'll go to a model on that site, list out the parts, and then click on the "KF" next to the parts picture to find out what other models use the same part. In this case the Pajero didn't pop up when I clicked "KF" next to the chassis...

[speedy_w_beans 4286]

Just a small update today... I blacked out the "nostrils" on the front grill, blacked out the screws, and added a star on the back. The back end was kind of bland with nothing going on, so putting something there to represent "Tamiya" or "Texas" seemed like a fun idea.

The body mounts are still soaking in bleach and aren't fully stripped yet. Maybe I can address those tomorrow. The last exterior flourish, and the one I've been avoiding, is the set of bull horns to mount under the windshield. In general I know what sort of look I want, but how to fabricate them is the problem.

I'd like to finish the body and body mounts, then go back to the electronics to complete the model.

[biggamehunter 127]

looks much better with the blacked out screws etc , great job , love the star !!!

[30YrsL8r 97]

I know I'm immature but I can't help smiling at the big brown starfish on the rear end!

[mr crispy 2297]

I know I'm immature but I can't help smiling at the big brown starfish on the rear end!

It needs a tail above the "Starfish"!

[speedy_w_beans 4286]

Nice smoke unit... I'd love to see a video of it running speedy

So here's a tragic comedy to laugh about -- "Mr. Crispy" asks for a video of the smoke unit running, and it melts down on the first test run! At least I hadn't installed it yet!

Here's a video of it running and melting...

https://www.youtube.com/watch?v=sBX4uWPDP28

I need to cut how much power is going into the box. Based on first measurements it was about 4.75 A * 4.75 A * 1.6 ohms = about 35-40 watts. Way too much for a small plastic box. I think to make the box survive the heating element can only consume about 3-4 watts maximum. While I could definitely get quite a bit of smoke running at this higher power level, I only need it to puff every so often as Bump Steer snorts. Back to the drawing board...

[bromvw 744]

So here's a tragic comedy to laugh about -- "Mr. Crispy" asks for a video of the smoke unit running, and it melts down on the first test run! At least I hadn't installed it yet!

Here's a video of it running and melting...

https://www.youtube.com/watch?v=sBX4uWPDP28

I need to cut how much power is going into the box. Based on first measurements it was about 4.75 A * 4.75 A * 1.6 ohms = about 35-40 watts. Way too much for a small plastic box. I think to make the box survive the heating element can only consume about 3-4 watts maximum. While I could definitely get quite a bit of smoke running at this higher power level, I only need it to puff every so often as Bump Steer snorts. Back to the drawing board...

Save yourself a lot of effort and buy a proportional Heng Long smoke unit . Fill it with the train smoke oil and its job done Buddie

[30YrsL8r 97]

Save yourself a lot of effort and buy a proportional Heng Long smoke unit . Fill it with the train smoke oil and its job done Buddie

If he's anything like me, he prefers the DIY option - just for the sheer h3ll of it.

What about a metal box? Thermal cut-off?

[mr crispy 2297]

Oh dear. Good to test these things before fitting them! That was putting out a great amount of smoke before things went south, I guess at that rate the oil wouldn't last long anyway. Was that just running off 7.2v?

[speedy_w_beans 4286]

Yes, the smoke unit was running from a 7.2V stick pack. Actually, the experiment wasn't a total disaster. I learned quite a bit just experiencing it in action. I think the small diaphragm pump moves enough air per stroke that I can connect a servo directly to it; that's a success to me. The puff and snort effect will be easier to control than I first thought. Just need to scale back the heating element a little...

[TA-Mark 196]

Using a bakalite type plastic instead of a thermo plastic would solve your melting issues. If you use metals, it will conduct both heat and electricity after it melts the wire's insulation.

A larger bellow with a quicker stroke of the plunger will make a longer, more powerful single 'snort' of smoke. The idea and first concept worked well though, until it got a bit warm.

[speedy_w_beans 4286]

I can't believe two weeks have gone by, but they have... After some household chores today I worked on making the horns. Here's the result before applying some shading... I'm still letting the putty completely dry before getting to that step...

I started with some quarter inch styrene rod and cut just a little shorter than the width of the Lunch Box shell. Then I used a knife and 60 grit sandpaper to taper each end. With an extra piece of styrene I experimented with a razor saw to see how many cuts and what sort of spacing were needed to get the curvature I wanted for the horns. Then I used the razor saw to cut slits about 80% through on the actual tapered rod, and applied cement in the joints to bond the segments together. This provided the overall shape. Then I used some Testor's putty to fill in the joints and coat the rod. Sanding with 100 grit sandpaper smoothed everything out but left some texture behind for dry brushing. Then I wrapped the horns in some twine, and for the picture they're just sitting on top of the fur -- no screws or glue yet.

To all who are following this thread, I'm sorry this is taking so long to finish. Our project team at work is under the gun to maintain a very tight schedule, so it's easy to log onto TC and leave a few comments here and there, but it's difficult to allocate hours for making progress...

[speedy_w_beans 4286]

I'm very happy today as I think a lot of Bump Steer's appearance is finally coming together!

As mentioned earlier, I had sanded the horns with 100 grit sandpaper. It turned out the best technique for getting some shading was to rub a finger on brown and black pastels and then transfer some of the dust over to the horns. The combination of rough sanding and fine pastel dust added some depth to the styrene and putty...

Then I went on a Monster Jam sticker spree, trying to dress up the chassis to look a little more like a real monster truck. I checked the Monster Jam web site for official sponsors and tried to match up as many of them as possible with leftovers from the Parma decals I had used on my Mad Bull. In the end I had to select some real-world sponsors that aren't part of the Monster Jam series just to complete the chassis. It's an ok compromise, and you never know if any of these sponsors will actually be a part of Monster Jam in the future.

[speedy_w_beans 4286]

A few more pictures...

[JeepnMike 150]

That looks badass!! The stickers and the shocks add a lot of realism.

[lawdog 23]

Excellent...all that's missing are these guys:

[mongoose1983 3362]

That is absolutely incredible. WOW!

[Psylence 25]

Hey Speedy, I saw this today and thought of your project. Wonder how similar it is to what you have come up with...

http://www.bigsquidrc.com/burn-effect-smoke-generator-for-rc-drifting/

[speedy_w_beans 4286]

Thanks for the link. It looks like a similar idea with a nichrome wire and smoke oil... I wish they would have shown some video of the cars drifting to see how thick the smoke is; I think you need to generate a lot to make it look realistic.

The hair dryer coils I have actually use two gauges of wire. Initially I started with the thicker wire, but I'm thinking now I should try the thinner wire since it will have higher resistance per unit length. I'm shooting for about 10x more resistance in the next smoke generator to cut the power quite a bit.

[speedy_w_beans 4286]

Well, four and a half years later this is going to be the first of about ten projects I hope to finish completely.  Since the last post in 2013 vaping has become more popular, and that is going to solve most of my smoke unit problems I had earlier.  There's a ready supply of atomizers, batteries, and liquids out there, so I won't have to worry about designing a heating element, the ugly smell of model train smoke fluid, melting plastic, trading off current vs. volume of smoke, etc.  I don't vape personally, but the parts are readily available and very inexpensive.

So the game plan right now is to use a receiver controlled switch to regulate battery power to both the guts of an aquarium pump and two atomizer coils.  The motor of the aquarium pump is meant to run on two 1.5V 'C' cells in parallel, so I'll need to add a power resistor to drop the voltage to the motor.  It's not particularly efficient, but since it will run intermittently it's not a huge deal.  Each atomizer is meant to run on a 3.2V to 4.2V LiPo cell, so to handle a 2S LiPo battery I'm going to wire the two atomizers in series.  So the series combination of resistor+motor will be wired in parallel with the series combination of atomizer+atomizer, and that whole load will be controlled by the switch on CH3 of the radio.

The aquarium pump draws in air through the black nub by the diaphragm; the diaphragm is cycled by the motor.  Air exits the pump through the gray nub; I'll use some silicone tubing to run the air to a small box.  That box will have the battery connectors and part of the atomizers internal to it; I'll probably use rubber grommets to seal the atomizers and some hot melt glue where the wires exit the box.  The tips of the atomizer will be cut down so silicone tubing fits over the ends more easily.  Then the tubing will go to the "nostrils" in the front grill of the body.

If all goes well I should be able to make a simple aluminum bracket to mount the aquarium pump, resistor, and switch to the battery tray at the top/back part of the chassis tub. The box with the atomizers should find a home right behind the steering servo.  One other modification I'm planning is a change to the bottom battery tray so it can accept a hard case LiPo.

More to come...

 

[Kingfisher 1175]

Interesting idea. When choosing the vape juice, you'll have choices of the mixture being more PG or more VG. Choose 100% VG. This gives off the most clouds.

[Grastens 2821]

I looked at the most-recent post and thought: "What has TamiyaClub gone to?!"

Now it all makes sense  Looking forward to seeing what you rig up!