Heavy Duty Power Functions Drivetrain . LEGO Technic Power Functions remote control drivetrain for heavy vehicles. 4 XL motors, 1 Medium motor, 2 Battery Boxes and 2 IR Receivers. .
I've had a few requests asking to see some more details on the Power Functions remote control drivetrain in my Fiat 682 Race Transporter, so here are a few bonus pictures and a (very) short video. There are builders on MOCpages who are loads better at Power Functions than me, so make sure you have a look at their MOCs too so you get the best information available.
- Drive: 4x XL motors
- Steering: 1x Medium motor with clutch
- Power: 2x 9V Battery Packs
- Control: 1x IR Transmitter, 2x IR Receivers
Cargo Area: This has enough room for all the Power Functions components. Here you can see three of the four XL motors driving the vehicle, and the two battery packs. The fourth XL motor is directly underneath the three you can see in this photo (so they make a 'T' formation). Each battery pack powers two XL motors and an IR receiver (mounted in the ramps of the truck). One of these battery packs also powers the Medium motor used for steering.
The Battery Packs' switches are connected together by the black Technic lift-arm thingumy you see arching over them. This makes it much easier to switch them both on/off as it forms a nice big handle that's easily reachable when you remove the roof.
Chassis: From left to right you can see; the differential, gearing down for drive, drive motors, steering motor and clutch, gearing down for steering.
XL motors are extremely powerful (we'll come on to just how powerful in a bit). As such the chassis needs to be very tough. The Fiat's uses four Technic beams, joined by cross members every few studs and plated to at least 2 thick both above and below. In addition, it also uses two smooth Technic lift arms to clamp the chassis together at the area under most pressure. This took a lot of trial and error; every time the chassis cracked I fixed that area - tested it, found the next area of weakness and so on.
Damage! Once the chassis was indestructible the next failure point were the LEGO cogs and axels. This is what happens when you miscalculate the torque being put through them (I also busted about 6 cogs).
This occurred when I went from two XL motors to four. Two XLs needed to be geared down twice (meaning a slower but more torquey model) to take the weight of the truck (4.5Kgs). With another two XL motors added I didn't need to gear the truck down so much, and the torque was so high it was twisting bricks! As such the truck is now only geared down once (as you can see in the second picture), and the gears are doubled and connected by both the axel running through them, and Technic pins, to take as much pressure off them as possible.
The truck is now reasonably quick and pretty reliable too, but it's taken a while to get there, so don't worry if your first heavy duty Power Functions drivetrain requires some tweaking!
I hope this helps answer some of the questions being asked about the Fiat. If you need to ask anything further please feel free in the comments section below. Apologies a few bits in the first picture are wonky - the truck was looking a bit tired that day after much fiddling/turning upside-down etc!
This MOC is part of the Classic Race Teams Project.
Happy Building : )