Part 2 link here soon: Building a vacuum box, first shell mold, fitting FPV and final video!
So I've done 1:64 and 1:48 scale both of which are massive fun but are pretty much limited to indoors only. When it comes to outdoors I much prefer off-road in some way over on-road only as you always have to find a nice piece of tarmac or similar to use it. With off-road the options for use are much larger.
I decided on 1:24 scale as a nice park type Truggy which is perfect for FPV, so not too large but can handle bumps and knocks without fear of braking the model. Specs are:
- 1:24 scale chassis: 180mm length, 90mm width. Although for THIS truggy I opted for a wheel base of 135mm for stability.
- 130 brushed motor on a 20A speed controller.
- FrSky TFR4 de-pinned and direct soldered.
- Corono MG servo
- 52mm diameter pin tyres.
- 2mm solid aluminium two piece chassis running 4mm steel axle.
- 10mm axle bearings and 3mm front wheel posts.
- EVERY bolt is 2mm (M2) in various lengths.
STL files for 3D printing are below, I did not have to use supports or brim much at all and generally printed at 50% fill for a bit extra strength. Exceptions are the front shock tower needs support enabled to bridge the gap where the chassis slots in, wheel hub may need support for the control arm if your printer fails on it.
The 3D design of this model was designed as a hybrid between aluminium and ABS. The shell design I created after modern day roadsters inclusive of air ducting to each side of the canopy area to help keep electronics cool. All wheel designs are to fit 52mm tyres which are pretty easy to source so that replacements are not a pain to find.
I created a simple chassis template that can be printed out and glued to the plastic coat side of 2mm aluminium sheet to drill out all the mounting holes and slots for the Velcro strap and the sprocket gear to sit in.
I figured I could get 3 full chassis templates cut out from a single sheet but opted to stick with one to begin.
The downside to using aluminium is obviously weight however for the strength and protection it gives I am not at all bothered.
All parts printed out ready for assembly.
I kept the wheel design fairly simple and as light weight as possible. The rim of the wheel is 1.5mm thick. These did not require any special printing requirements like brim or supports as long as you print them face down.
The two chassis sections use a regular hinge to piece together. I opted to do this as it's stupid easy to replace and from pretty much any hardware shop. Past that you can see the sprocket gear cover to protect the gear.
The rear towers double up to provide the shock damper pivot points and house the rear axle 10mm diameter bearings. I wanted to reduce rolling resistance over the last 1:48 model so rear bearings was the best way to do this.
The front wheels being a Truggy require independent suspension. So as well as a wishbone the wheels must pivot with the angle of the suspension otherwise the wheel will camber in (lean in) as the suspension goes up and vice versa camber out the more the suspension drops. So the wheel needs a C cup which can pivot on the wish bone and a pivot arm up top to keep movement equal and keep the wheel camber exactly in place. The threaded rods means I can adjust the camber later also. The wheel hubs pivot within the C cup and house a 3mm threaded bolt for the wheels to sit on.
One of the earlier prototype designs used a cheaper servo which broke pretty fast so I used a Corono MG servo, unfortunately the servo lead comes out the back but the design calls for the servo to sit flat on the chassis. I simply notched out an extra slot for the wire to exit out a different direction.
To protect electronics I designed a RX box which allows the receiver to sit inside and wires come out between rubber pieces to seal the box, everything is designed as push fit so the top doesn't need screws or bolts to stay closed.
The front shock tower design means it slips over the chassis from the front and uses bolts to pin in place, there is zero play and is very secure. With the wheel assembly complete the steering servo can be fitted with the front bumper.
With the receiver installed I could configure the steering and add the steering control arms from servo to wheels. Again this uses 2mm threaded rod so toe in/out angle is adjustable.
Here you can see the last major design change when I opted to move the speed controller off the back chassis and instead have it attach to the lid of the RX box. The bulk of the electronics are now all stacked in the center of the chassis next to the battery. The on off switch is also much easier to access with the speed controller in this configuration.
For now I am using a 450mAh 2S 65-130c lipo battery but it's clear to see that you can fit a much much bigger battery than this if you wanted.
To reduce the complexity of the drivetrain I mounted the motor over the rear axle and again went for direct pinion to sprocket gear on axle. The motor simply plugs into a lead coming from the speed controller.
As I'm not 3D printing a shell this time simply because its too much material and it'll not be strong enough I decided to try my hand at vacuum forming which I have not done in roughly 20 years. But by creating a mold to vacuum form off it does mean I can make as many shells or anything else I want.
The build of the vacuum form box will be posted as an additional project later on.
To create a shell mold was a lot more complex as it's obviously a large shape and I do not like wasting material AT ALL. I spent a long time figuring out the best way to print as hollow as possible to use the least amount of material.
In the end it used a little over 100g of material to print with just enough fill to stop it collapsing on itself during printing. Any defects can be sanded down or filled prior to use.
Now I have a working chassis and a mold ready to pull lexan over to make my own shell.
