So the first step in How It Starts for us is Ideas. Why are we designing it and how are we gonna achieve our goals.
First let us start this whole project off with a disclaimer. Nothing we say is the way anyone has to do it. Nothing we say is from years of school or training or even reading engineering books. We are hobbyist and have been for over 30 years. What we design is test-try-refine for a lot of our stuff but its all tested by us. The ideas and designs come from our years in Rock Crawling and much of the history and info we have found from other veteran drivers. Together we all in this community have lent a hand in our designs. For that I say Thank You to all the OG’s of the sport who helped teach us along the way.
Now back to our beginning. For this lets base the whole story off our latest release, the Pneuma and how we came up with some ideas.
The Axial Capra really pushed us to bring back a project we worked on in 2018. Lets go a year before that though and dwell on how our mind was looking to bring portals to 2.2S comp rigs. Portals are not something new to us, many aftermarket companies had options out there. As drivers though we tend to follow the normal and not many look for that odd ball creation. Some do, dont get us wrong but for the comfort zone we tend to stay with what everyone knows.
So after a year of looking around at options and honestly not liking many, we came across what we felt was the best option. High Altitude Performance did the leg work and made portals for through Shapeways. Designed by a veteran crawler we knew we could trust the intention and integrity of the designs. We ventured out and got our parts together.
From that creation we were on a mission. At that time we had the Nationals coming up and quick. With 4 months to put this truck together we had our work cut out for us. We wont go in to much about what we had for obstacles but some may remember our Orange truck from 2018.
This was a big learning curve on everything we knew. From all aspects it wasnt just simply adding portals to an un-Stuck chassis. We had to work in steering, think about our CG, work with different shocks, custom cut tubes and most of all have it done in less then 4 months. This was the project that really showed how important a role our 3D printers were gonna be.
Well we didnt win any title with that truck but the amount of information we got from it was incredible. We knew portals could be and would be the next evolution in comp crawling on a shafty rig.
Now fast forward to the Capra. Having this truck come out sparked our desire for another portal rig. With XR10 width axles, improved plastics and the backing of a company that started the craze we jumped into our notes.
Where do we start? Well first we took our measurements for everything and added in shock/locations and set our drawing out at our maxed wheelbase of 12.5 ”. After that we look at where we think our weight bias would fit best and find our skid center. Now I will say NO we arent gonna give any of our secret sauce to the math we use but the tools to design your own are out there.
First we tackle the skid and lower link lengths and with our 2018 notes and the successful un-Stuck kits we had our baseline. After that we work in our ‘preffered’ shock angles and mark our locations. We have our theories on shocks and it has worked well on all our rigs so we stick with what we know. Again there is no right or wrong way to this, its all from years of trying.
After we have that its just a simple task of designing the truck around that.
We have our v1 chassis at that point. From there we look at what transmissions are available and how to work them in. Now that puts us up to v3 and into our 3D models. We have a chassis – but we arent going to cut material before we know things fit.
Skid plates do so much more then just tie the lower links to the chassis or give the transmission some where to go. They really play a crucial part in things like torque twist and roll centers. This was something we learned much about with our Nationals truck.
Disclaimer: This is our experience and more then likely the wrong way to explain it but here it is. We use this little write up for some key information to how we design our skid plates. Click Me
To quote a piece from there: ” the lower links resist thrust.”
We use this for thinking about torque twist and with portal axles we generate more of it at the wheel due to the added reduction. This triangulation also effects our roll center, with the uppers as well but for now we’ll talk lowers.
More triangulation at the skid is going to let the chassis roll easier under power, lean or torque twist as we think of it. Add that to the fixed upper link mounts and we effect axle steer as well. Basically yes the chassis will roll easier and allow the axles to work smoother but we are fighting the dynamic weight changes from our chassis.
This is taking weight off our front and moving it around. Bad for climbing and side hilling. Now the Capra has a lower link geometry we were familiar with from the Losi Comp Crawler. Different axles that didnt generate the torque twist like the Capra but we worked with a couple variations and found a happy spot to settle it down on the Pneuma. We actually gave the adjustments to change that roll point a bit.
Heres our picture of figuring out all our lower link roll centers. Our theory is simple, what ever axle has their lower links converge the closest to the opposing axle has more control over what that axle does.
If our rear links converge closer to the front then the rear effects the front greater. Lets say a push for lack of terms. But if we converge our front lowers closer to the rear then we may find the rear isnt allowed to work as smooth. An example would be on a down hill and navigating a turn. The front starts to wag the dogs tail and move the rear around too much and hit a gate or not stay on the intended line. Or vice versa where we are trying to climb something and the rear will push the front off line and cause us a reverse or a gate penalty.
Its a balance act but heres where our eyes stair at best possible scenarios. Each line shows us possible convergence points. Trial and error is really the science to this part in our opinion.
Now to the 3D of Autocad Inventor and we work up our first skid.
Heres another skid we’ve worked on for the Gen2 line. You can really see the benefit of 3D printing at home, we can try so many options.
Now we have our chassis and skid designed, its off to the 3D printers.
As much as we wish 3D printing was instant we have to wait. Oh we almost forgot the fun part of 3D designing, seeing it all come together. The best part of modeling everything, putting it together.
So that brings together basically our starting point. We put ourself to the spot of having printed parts to assemble and a working model to think about our decisions.
Keep on the look out for more of how we think our ideas up and what we put into the Pneuma chassis.