Try a smaller Bass Reflex speaker, so long as it has the correct rating will be fine if not cheep but better than building another vehicle to add to it. I have used a couple in my 2 space challenged Steam Trams.So a little progress (photos to follow), I tried the MFA 12 - 24 volt motor, first with 7.2 volts and then with 12 volts (NiMH), and with the lower voltage poor and the higher okay ish. So I tried the "cheap" Chinese" 6 - 12 volts motor on 7.2 volts, wheels spun well, so a uncontrolled test around railway. I hadn't considered weight, and being ply the the wheels spun and almost no traction, just over 1kg of weight added and it ran very well, fast than I would normally run it but with the RC added this would be controlled.
So I will be powering this with Li-Ion 2S (7.2 volts), and I was considering a MR001a Rx and 12 volt 30 watt ESC. Also sound with a MLS Railcar card, however the speaker could be fun to position, and I was considering a "baggage car", just for the speaker, however I would assume if run without the speaker the MLS would have to have a dummy load, or be switched off.
I now need to go and take some photos of the progress before I get any hassle
Oh just had another thought my other get out of trouble with speakers is roof mounted either on a luggage rack with a tarpaulin to cover it or inside under the roof.Yeah, the problem with tiny prototypes. If you go for a mini speaker, you'll get some realistic noise from an MLS sound card (I've used that set-up on my Yeti)
I don't seem to get much speed variation in the sound - it picks up from idle and then seems fairly constant and that's running 12 volts - but the gearing is fairly low, about 1:30 and the motor is fairly light. I boxed the speaker in to set it back about 3mm from a plain oval aperture to give it a little bit of resonance. When you decelerate, the motor shuts off nicely for a very brief spell - that also sounds realistic, but that's a diesel loco sound card, not a railbus. (My railbus card is set to US sounds for the Goose so I don't know what it would produce for an Irids railbus Probably, instead of 'All Aboard' it says 'Guinnes is good for you.'
There still won't be much room in there. Compare it with my VW, and I have a manual speed control because I don't operate the drasine, I just pop it on the track and watch it run, the motor gearbox is pretty small, and then I have the three AAA batteries sitting on top of the rear wheel arches. I have retained the front seat, and the Chinese manual speed controller is much larger than a Deltang Rx / ESC.
It's a challenge; looking forward to the photos