Gr. CM Hillclimb Prototype Project

Hello Everyone!

I recently joined Racecraft HQ to expand my knowledge about chassis and suspension setup and I'm also super interested in the Data Analysis Courses and can't wait to discover what come next!

So this topic makes sense I'll sum up my background. I've always been interested in cars and motorcycles, but it was only on my second of my Bachelor's in Mech. Engineering that I decided to pursue a degree in Automotive and after a Masters in Motorsport to better understand race cars and design my own! And work in motorsport of course, altho I'm still not sure in what field 🤔

Anyway, (I hope this makes sense being posted here) I'm here to ask anyone that could help me gather as much knowledge and advice for the project I've started a few months ago where I'm researching and intend on designing a Hillclimb Prototype to compete in the European Hillclimb Championship! I am very new to "Race Car Desing" let's call it and I haven't the faintest clue what to look out for or where to put my chips and the design path.

Can anyone give me advice on this? Anyone who has developed or built a race car and/or a tube frame chassis and composite fairings with aero development.

Hope that this topic is appropriate to post here :)

Thank you for your attention and help!

P.s.: I am talking to a race team to shadow them and study their Bango Rancing Cars (BRC) B49 and if possible another team's Silver Car EF10! But that's still in the works due to the thing that shall not be named limiting the amount of people each pilot can take with them... Hopefully soon! (Pictures atached)

Hi Eduardo, welcome!

Hillclimbing is a fantastic discipline, you'll have a lot of fun building cars for this type of competition. There's also a lot of opportunities to continue improving what's out there. There are some people building cars like this to a very high level already, however as I'm sure you have seen for yourself, hillclimbing is one part of motorsport that has many cars with a lot of "room for improvement" even just with the fundamentals. It's not uncommon to go to one of these events and find many examples of single shear attachments and huge bending moments 😱

It's a big project you're taking on, will be interested to see what our other members have done that may relate well to what you're doing. Keep us updated as you go 👊 - Tim

As Tim said, HCs are a lot of fun, and there's a lot going on in a very short period of time.

Brecause it's very driver intensive, and they're usually very short, I'd suggest using as much data aquisition as you can so you can see what the car's doing and corrolate that to the driver's input on what's happening.

As Tim also said, seems like a fair bit of looseness where basic design fundamentals are concerned - some may feel that as the cars are usually very light it isn't important - but it all helps, and with aero' and high spring rates, plenty of potential for uncontrolled deflection, which is a no-no.

What class are you looking at, and what vehicle - many will start with something they have lying around which can be a problem if it's fundamantally unsuited, rather than looking in the s/h market for something that is going to be much more practical in the longer term.

Thank you for your support, Tim and Gordon!

Regarding the "flimsier" nature of Hillclimb race cars, the first time I saw one without fairings on I genuinely thought to myself "Is that all?" because of how little car there was. Through my university, I was able to join a race team where we had a couple of Osellas, PA21S (Cat. CN) and PA 2000 EVO 2 (Cat. E2-SC), that were K20 NA powered ranging from 265 to 340 hp and Sadev sequential gearboxes so those actually looked reasonably well built, although chassis around the cockpit left a bit to be desired.

That design improvement on torsional rigidity and the somewhat weaker parts where their deflection could be reduced is definitely something that I intend on addressing with my project. I'm thinking of experimenting with topology optimization to try and discover the best layout for the chassis, but I'm not sure how I would set goals for it, for example, what (if it's possible) torsional rigidity targets I should aim for. Any tips?

Gordon, the project I'm working on is a Cat. CM Hillclimb Prototype that based on a bespoke tube-frame chassis motorcycle powered flat floor and composite fairings type of race car (As you can see in the pictures I attached to my first post). So besides following the regulations on that, the base vehicle only matters because you can't change a few things, like part of the intake and the gearing on the factory motorcycle engine among a few other things.

And the cars that can be seen in those pictures, I am counting on having access to them when restrictions lift enough for me to be able to attend my National Hillclimb Championship and study them (should happen by the end of the month). I am not sure what exactly I need at this time, since it's my first full from the ground up vehicle design, so I'm trying to make a plan for that but I'm also going to ask anything I remember and take a boatload of pictures and definitely will take every measurement I can!

Besides that, I am still analysing regulations (which is interesting but also a total mind-melting conundrum sometimes 🤯) and studying and gathering every piece of information about the two cars in the pictures and also every other race car I can!

Any tips on what to look out for when doing a project like this? Any rabbit holes I should try to avoid?

Again thank you for the support! Will definitely keep you posted! 👊 - Eduardo

P.s.: Also any tips on analysing regulations so I don't lose my mind? 😅

Eduardo, I wouldn't get too hung up on trying to invent something too novel. Learn from the best cars out there and think about the problems you see with them. You really need to start with an overall concept in mind - as in something that can help guide you through every design decision. There will be a lot of them along with compromises at every point. Just for example, is your concept ultimate lightweight? If this was the case you might make some compromises on compliance and even safety (not recommended!). Alternatively, your concept could be high downforce (obviously this will depend on the type of competitions you'll run in), in this case you may be prepared to make compromises in kinematics to maximise your aero.

There are a number of studies out there on torsional rigidity, but a good starting point is to aim for a torsional stiffness of at least ten times the antiroll stiffness of the stiffest axle. Going for a target like this will give you a chassis that responds well to setup/stiffness changes.

If I was building a motorcycle powered hillclimb car from scratch for medium average speed with the requirement for some very tight corners/chicanes, I would be prioritising low CG and low yaw inertia. This is just about minimising load transfer and maximising yaw acceleration for a given yaw moment. This means centralising mass as much as possible both laterally and longitudinally!

Tim

Yes, the topology optimization is more of a way for me to learn the tool and how it can be useful for making parts, or a chassis, that's as stiff or safe as is needed while being as light as possible. It's more of an experimentation, and if it helps me create a chassis that is objectively better then great!

As for the concept, I am a fan of Colin Chapman’s “Simplify, then add lightness”, of course, that it will be without compromising on the safety! As for the speeds, I'll need to analyse the courses and ask the team every bit of information I can about top speed, corner radii, etc. to figure out what goals I need to set for the car and where I need to compromise on to achieve a competitive level with those cars.

I'll keep that ratio of stiffness in mind! And thank you for the tips on the low CG and low yaw moment! I was making a list of goals to strive for but I hadn't considered the yaw part, thank you, Tim 🙏

Talking about the size of the vehicle, centralization of mass and all I am wondering about something. In the regulations, we have the max. dimensions l*w*h of 4500*1900*1030 and both the cars that I found that compete in the CM category are within a few mills of each other at 3750*1.750*1.030. The car height is maxed out but I saw that the driving position is very upright (as seen in the picture below) I'd almost as more of a GT type of position. I didn't find a reg. that defined the drivers seating position in any way. Could this be a compromise to make the car shorter and therefore lighter to achieve the dry weight of 450 kg? I struggling a bit trying to understand why they'd make the car a full 750 mm shorter and 150 mm narrower than the regs. allow.

Any insights on this?

And again, thank you for the advice. It's really invaluable to me!

- Eduardo

Longer and wider cars are not as good in tighter sections, becoming harder to turn through tight corners, especially if there are elevation and camber changes through the corner. In the faster sections they will be more stable but you may find that a trade off has been made to have more responsiveness in lower speed areas and sacrificing some stability (though the aero possibly helps cover this) at higher speeds.

One area to be aware of with a vehicle like this is ease of maintenance, from my experience with hill climbs, contact with objects other than the road surface are common, so being able to quickly and easily replace or repair parts makes running the cars easier, and reduces the chances that a minor off means the end of competition until the vehicle gets repaired back at the shop.

Some thoughts, that may be quite incorrect.

As Tim and Steven suggest, a low polar moment of inertia can make the vehicle much easier to rotate, but also much easier to spin.

One may indeed expect the vehicle to have the tyres spread as wide as the rules allow, to reduce the load transfer and maximise the tyre grip, but there is the other side of the issue and that's that a wider track needs more track width and can't 'cut' corners or straighten the road to the same degree - it needs to be 'swerved' more. A wider vehicle also has more frontal area and hence drag - but on the other hand, there's less width for aero' to be used for downforce. On load transfer, keeping the centre of mass as low as practical should help everywhere.

A longer vehicle, especially wheelbase, also needs more steering input and more radius for the front tyres to move through - think of a truck vs a mini, the latter has a tiny turning circle in comparison.

The driver's cockpit are has two important functions, fortunately complimentary, in that it plays a critical part in protecting the driver and provided most of the stiffness to the chassis as it's a large opening between the front and rear chassis mounting points. On that last, I'd suggest concentrating on the chassis stiffnes/strength between the suspension hard points, the outer ends really only need the strength to resist the vibration and bumps, plus any aero' devices, which could be directly bolted to the chassis, anyway. It's something we tend to actively ignore, but there is a very good chance you WILL crash, build the car with that in mind and it'll keep you much safer if something does happen.

Steven has a very good point about maintaining, and repairing, the vehicle - with some thought you may be able to design suspension parts, for example, that can be used either side, so cutting down on spare parts.

First of all, thank you all for the feedback and the tips. It's been really amazing, even in this short forum post having all of your guy's advice! Thank you! 🙏

And about the maintaining and repairability of the vehicle, I'm aware of how critical this is because in my previous team one car had a small off, in this same event I'm attending actually, and the car was out of commission cause they broke the upright and the lower A-arm of the FR corner and we didn't have the right parts... So, and as an example, I'll try to design as many parts as possible to be interchangeable between the corners of the suspension. Already have a few ideas to do this for the uprights since it was a problem that I've faced before that was preventable!

(I loved all the advice, this matter of the data gathering is just a bit more pressing due to how scarce these opportunities being that the team doesn't even know me and they are trying to get me a "competitor's pass" to be able to join then when there's no public allowed and team sizes are restricted 👌)

Shifting gears to a different matter, I'm going to have the chance to be a part of a race team in a Hillclimb during the last weekend of May (being that it who shall not be named will allow it 🤞) and I have many questions about data acquisition! I've never done anything besides asking questions, a few pictures, light work on the car and observing. I'm 98 % sure that the car has no data logging system whatsoever and besides my Garmin 910XT that has GPS where I can record speed and save let's say "layout of the track" on the map (I'm not sure what type of file the watch sends the MyGarmin page to be able to retrieve that info, it's a bit beyond at the moment) I don't have anything else that I can put on the car to retrieve data.

Any tips on how to acquire data from a hillclimb run that is cost-effective? And what other data I can easily acquire from the run? Besides asking the team for the onboard videos.

And I'd love to measure up the car, but I'm not sure how to do it well enough so that after I am able to create an accurate 3D representation of the suspension geometry or how to do it considering that I'm going to travel 230 km to be at that event (the team is local, so it's not easy to take time of the week to go there...) and I'm not sure what I'll be able to do in that setting, a.k.a., with covid restrictions and all plus being during a 2-day race event 🤔

Any tips guys?

Thanks in advance

- Eduardo

P.s.: I have a tendency to write a lot, even when I'm trying not to 😅 please do tell me if the posts are too long or can be better explained. Thanks 👊

No problem on the long posts Eduardo, it's good you have so much to say =)

Regarding data acquisition - it sounds like you'd really benefit from taking our Data Analysis Fundamentals course. There is a lot of info in there about selecting a logger as well as the analysis itself. If you are looking for a very cost-effective option, there are multiple companies out there offering apps that you can run on your phone. Ultimately, your phone has a lot of built-in equipment you can make use of - GPS, accelerometers, video. There are even some options that allow you to connect to the CAN bus and log sensors from your vehicle.

This is still very entry-level stuff, but you can start to learn about things without spending much money in this way!

Regarding making a 3d kinematic model of the suspension, this is actually something I'm going to cover in our upcoming suspension fundamentals course.- specifically the practical measurement of the hardpoints of your car. This course is about 6 weeks away from completion at the moment.