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Fire and Rescue and Emergency Vehicles Here is a spot for all them important emergency vehicle builds.


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  #121  
Old 09-06-2020, 10:13 AM
Tgrzes Tgrzes is offline
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Default Re: Scania airport fire truck

Amazing detail throughout! Is all your diamond plate painted styrene?
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  #122  
Old 09-07-2020, 09:36 PM
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Default Re: Scania airport fire truck

Yes, it's all styrene. I don't have the patience or equipment for metalwork. Plastruct 1:16 scale diamond plate number 91683 to be exact. The other styrene is Evergreen.
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  #123  
Old 09-09-2020, 08:26 AM
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Default Re: Scania airport fire truck

Can I also ask what kind of battery setup you have and what kind of run time you get approximately? I picked up a cheap pair of 7.2V 3600mah NIMH batteries to get me through build and testing, but I have no idea whether one will be sufficient or if I’ll need a second battery for the pump, solenoid valves and lights. I assume I could get to it using some math, but I’m just looking for a rough idea so I can plan for battery space.
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  #124  
Old 09-09-2020, 08:58 PM
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Default Re: Scania airport fire truck

I did the planning for a NIMH, but because of the specific mix of electronics I ended up with, I went with a 2s Lipo pack (Standard r/c car hardshell pack, same size as the NIMH stick but rectangular). 7,4v 5000mAh, I think. I ran into some edge case issues because the NIMH pack will start out around 7,8 and discharge down towards 6v and give issues with some of my voltage regulators. The Lipo starts at 8,4 and stays above 7v during its useful range.

Will the solenoids work at 7.2v? I also hope you describe your plumbing in details, including where to find the tubing, valves and connection hardware if you're going that route, as I chickened out and went with tank -> pump -> monitor and an option for a second pump for filling the tank.

If you go with Lipo, there are many sizes to choose from, and even the hardshell racing packs come in a compact "shorty" version.

With regards to runtime, I haven't actually been running it enough to give a good answer. I'd guess 30-80 minutes of real playtime based on prior experience with other cars. I can easily do short test runs and long light/sound testing sessions several times in a week without charging.
Guesstimation factors: 3500 mAh NIMH would give me just under an hour of runtime in a Tamiya m-03 with some lights and with a CC-01.
My LEDs theoretically draw ~740mA. Arduinos + receiver + sound is roughly the same. I think the pump was around 2A last time I checked, but it drains the tank in a minute or so and won't affect runtime much.

If I were to plan it out all over again, I might consider going 3s for something closer to 12v to get some extra power to the 12v pump. That way I could also go with a smaller pump instead of running an oversized 12v pump on 7-8v. I'm also using a boost circuit to boost the battery voltage to 9v for some of the LEDs to allow wiring them in series where the space is extra tight and could avoid that with an extra battery cell.

I don't think I've uploaded a diagram for my power setup yet.
I've set it up so I can use two power sources: An R/C battery pack for everything or a USB port for low power lights only (display mode).
The battery wires split through switches into 3 main branches: pump (esc), drive (esc) and electronics. The drive ESC has an onboard BEC supplying steering + gear servo.
The electronics branch split into:
A: BEC (vBatt->6v for servo and lights).
B: Boost (vBatt->9.5v for high power LEDs)
C: vBatt into Arduino mega (onboard 5v regulator)
D: vBatt into Arduino nano (onboard 5v regulator)
E: sound (vBatt -> 3.3v for sound amplifier board and ESP32)

Most of the LEDs are on a separate voltage bus that I call vLED. This bus can be connected to either the BEC for 6v operation on battery or to USB power for 5v display mode through a switch.
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  #125  
Old 09-10-2020, 12:10 PM
Tgrzes Tgrzes is offline
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Default Re: Scania airport fire truck

Wow! Great info. I have a lot to think about! The pump I have is rated 6 - 12v and the solenoid valves are 3.5-24v. Both seem to be working fine with the 7.2v battery.

I have some windshield wiper tubing that I’ve been using during tests, but I’m going to see if I can get some of the tubing you recommended for the monitor. I picked up 6mm ID x 12mm OD black silicone tube; it’s a perfect scale match for the 6” hard suction that we use for drafting. I originally didn’t think of filling the tank thru the pump, but now that you’ve mentioned it, I think I’ll include another solenoid valve for tank fill while drafting. I’ll post plumbing details in my thread when I get to that part of the build. Thanks again for all the electrical info!
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  #126  
Old 09-12-2020, 02:04 AM
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Default Re: Scania airport fire truck

6x12mm silicone tube is what was included with my main pump. I'm also using some of that for the same purpose. It's very stiff, but I inserted a bent large paperclip to force it to bend the right angle when stored on the top of the tank.

Block diagrams for power wiring below. I don't know how much sense it makes to anyone else. You may have to download the full size version to read anything.
https://i.imgur.com/THFX3gU.png <-full size


One of the most important thing to plan out with a complicated electronics setup is the negative/ground wiring. I have frequently had to rethink and review the diagrams to avoid ground loops or accidentally sending motor currents through signal wires. I've tried as much as possible to send all ground paths in a star pattern back to central points closely connected to the battery.
For example, one critical point is the signal path that sends the SBUS signal from the receiver to the Arduino mega. To ensure that the difference between ground and signal voltage is the same at both places, one might usually directly connect the ground between the two components, but that's risky when they have different power sources. For the final design the signal goes from receiver to esp32 to arduino mega. The ground path goes back to the ESC, through the battery wires to the central distribution board and then to the arduino mega. Including a ground wire with the signal wire could send several amps of servo current through the ground traces on the arduino mega itself, or even motor currents, at best raising the voltage on the ground traces, at worst burning the arduino.

I still feel doing a master battery switch was correct, but now I would have placed a switch on the "drive" branch too, so I could disconnect the motor while testing. A switch on the pump seemed like a good idea to avoid water accidents and the idea behind the switch on the electronics branch was so I could disconnect it while developing the arduino stuff. Of course with the arduino stuff mostly done long before the truck was driveable, that switch is quite useless now.
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  #127  
Old 09-12-2020, 08:48 PM
Tgrzes Tgrzes is offline
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Default Re: Scania airport fire truck

More great info - thanks! I’ve been thinking along the same lines for power distribution and master switches. I’d like to learn Arduino some day, but for my build, I’ll be going old school mechanical switches on servos (except for the drive ESC).
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  #128  
Old 09-23-2020, 06:51 PM
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Default Re: Scania airport fire truck

Just curious...do you have more work planned for this truck?
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  #129  
Old 10-03-2020, 09:44 PM
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Default Re: Scania airport fire truck

It's definitely not done. There is still a long list of exterior and interior details, maybe some waterproofing, some structural fixes.
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  #130  
Old 10-28-2020, 02:18 PM
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Default Re: Scania airport fire truck

I was looking thru your pictures again, specifically ones where you're hiding stuff like switches and pumps in compartments. I was just wondering how the doors to those compartments articulate and how you keep them closed. I'm not at that point yet, but I've started thinking about how to possibly handle it. I was thinking of maybe using very small magnets.
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  #131  
Old 10-30-2020, 01:20 AM
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Default Re: Scania airport fire truck

The only compartments that are actually articulated are the lower rear switch boxes as seen at the bottom of post #2 and #44. I made a reasonably scale accurate but simple hinge with styrene and 2mm brass tube. Keeping them closed was an issue. Friction fit is an option, but in the end I went with tiny magnets and an M2 metal washer in a corner of the door.
The lower side plates (and the rear wheel arches) for the center/tank module are long plates attached with cube magnets. I suggest 1 cube magnet + 1 screw per corner, as that makes it adjustable.
The shutter doors for the front/pump module are pretty much plastic sheets attached with cube magnets in a way that lets me push the top to flip up the bottom (small piece of plastic tube in the middle to force the plate to rotate around the center).
The Rear shutters are not designed to open, but they are slotted in so they're removable after taking off the rear module for maintenance.
You might find that the magnets are strong enough to crack the glue and snap off if you let them slap together, so something softer than CA glue is advised.

edit: I'm using 4 or 5mm neodymium cube magnets. They're very strong, small enough to fit and large enough to not lose track of them. I'd love to use smaller cubes, but the thought of handling those tiny things without losing a couple in my eye or something honestly scares me. There's also an issue of pets or kids accidentally eating them if they fall off. I also have a variety of small neodymium disc magnets for other places like the interior ceiling.

Last edited by Wombii; 10-30-2020 at 01:31 AM.
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  #132  
Old 10-30-2020, 08:34 AM
Tgrzes Tgrzes is offline
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Default Re: Scania airport fire truck

The pivoting door was one I wanted to test, so I'm definitely glad to hear it was something you used. Seems simple to construct and adjust. Yesterday while working at my desk, I pulled apart a retractable pen and started playing around with the push button mechanism, lol. I think something could be done with it and it would be a nice feature, but ultimately too much trouble. The info on the magnets will also save me some trial and error. Thanks for the great info again!!
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