Design & Construction of a Human Powered Race Vehicle

2013 This report details the design and construction process of the Terzo Racing race vehicle built in preparation for the 2013 Australian International Pedal Prix in Murray Bridge, SA.

Matt Sullivan

HPV Construction – Terzo Racing – April - September 2013 Human Powered Vehicle (HPV) racing is a sport in which teams of 6-10 riders ride a pedal powered vehicle optimised for speed using a recumbent seating position and a fairing that fully encloses the rider and chassis. Races are endurance based and range from 6 to 24 hours in length. The vehicles have typical top speeds of around 60kph and the top teams are capable of covering 1000km in 24 hours. I have been involved in this sport since 2006 when I started high school. Since finishing school I have joined a community team with other former students of my high school. As well as racing the vehicles, a major part of the sport, especially for me as an aspiring engineer, is vehicle design and construction. Throughout my years with the school team I was involved in designing and building the race vehicles and built my own training trike in year 11. The following pages document the design and construction of the first vehicle built by me as part of the community team ‘Terzo Racing’.

Design – April

After the Wonthaggi 24-hour race in late March, we decided we would use our sponsorship funds to construct a new vehicle in time for the next 24-hour race at Murray Bridge in September. During April we had a number of discussions to determine what we wanted in a new vehicle. The key aspects to work on were:

• Increase track width and wheelbase for stability and handling • Keep the vehicle as low as possible, both seat height and roof height, for improved

handling and aerodynamics • Adjustable seat. We had previously used foam padding inserts to allow for shorter riders,

however, substantial amounts of padding result in loss of power. We wanted to keep the seat as solid as possible to direct more power into the driveline

We had had a number of rollovers at the previous race and felt that we could improve this. After this consultation stage I took measurements on our previous vehicle and used these to create the first designs of the new chassis. The wheelbase was increased by 30mm and track by a similar amount.

A ‘standard’ chassis design consists of a ‘spine’ that runs from the bottom bracket, below the seat, to the rear fork. Having this spine below the seat, limits how low the seat can be positioned. So, to drop the centre of mass lower, I opted for a ‘space frame’ design in which there is no spine. The structural components of the chassis run alongside the seat. The result is that the only component between the seat and floor is the chain. It is also a more efficient use of material, as a greater proportion of steel is a structural part of the frame rather than having material solely as part of the seat.

Figure 1 'Traditional' HPV design (Photo from Trisled)

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The new space frame design produced a number of challenges. Firstly, the boom running from the bottom bracket stopped at the front cross member (between front wheels). Running a single length of tube would not be strong enough, so it was decided to turn the cross member and boom both into triangles of thinner material. From the front cross member backwards, another triangle was formed either side of the rider. The other major structural section is the rear triangle that attaches to the dropouts, adding strength to the rear fork as well as providing a place to attach the seat’s headrest.

Figure 3 Final designs used during construction

Due to the rider being between tubes of the chassis, these side sections needed to be wide enough to fit the rider, yet narrow enough to allow appropriate wheel movement. I took measurements on the previous chassis and allowed for the wheelbase increase to determine how much movement we needed. I had to push the limits with the wheel clearance to allow plenty of room for riders in between.

Other aspects of the vehicles design such as steering were kept the same as previous vehicles I have worked on with the school. The angles of the Ackermann steering system were kept the same since we know that they produce desirable handling and tyre wear from previous experience.

Figure 2 3D image of front section design

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Construction – May - September

Once the design was finalised, a jig was made for construction of the chassis. It was during this stage that the correct angles for steering were set. The angles used are based on previous vehicles built by the school that were developed over 20 years and 35 vehicle builds. During this period we also began machining components such as kingpins and front axles and steering components. The kingpins, which are the axis that the front wheels turn on, were different to previous ones I had made. Since the wheels were to be enclosed inside the vehicle, the axles needed to be separate from the kingpins so they can be retracted to allow the wheels to slide upwards. This meant we needed to accurately mill flat sections on the axles and slots on the pins that matched up and were a snug fit. It was also more difficult to weld, as the material was much thinner in some places.

We spent the first couple of months working on these parts as we were faced with a delay in the sponsorship funds as well as an incorrect shipment of the chromoly steel. But by the start of July we were finally ready to begin chassis construction. The first 2 days of construction consisted of me cutting, fitting and welding the chassis components by myself.

Due to the fact I was living in Melbourne and travelling to Wonthaggi to work on the project we were faced with time limitations of a few hours each week. After 2 days spread over 2 weeks, the majority of the chassis was complete. After this we reverted to our regular Friday night sessions with other members of team helping to complete the chassis and other components.

Another problem that needed addressing was that since the boom and cross member came to a T-intersection, the forces were focused at that intersection and not spread to the sides enough. This was anticipated but was left until the construction phase so we could test to see the extent of the issue. It resulted in flexing in the frame (length ways) that would have caused a loss of power while riding. To solve this I added 2 thinner tubes running from this intersection diagonally out to the sides to help spread the force. Also, a small webbing was placed in between the 2 side bars on either side near the front of this section. This acted to join these components together and complete the triangle to stiffen the chassis lengthways. A principle of the design was to make the chassis as stiff as possible lengthways, to direct as

Figure 4 Chassis after the first day of construction (6 hours work)

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much of the rider’s power into the driveline rather than the chassis. However if the frame is too stiff in the perpendicular direction (between wheels) it causes handling issues and increased tyre wear while cornering. Some flex in the frame here is acceptable, to absorb the cornering forces. The extreme of this is seen in carbon monocoque vehicles that are so stiff that cornering is visibly rough. I intended on finding a level of stiffness that provided comfortable cornering as well as limited power loss.

At this stage we ran into a problem in that the rear wheel gap had contracted more than expected after welding and the rear wheel wouldn’t fit. This was solved with little fuss by using a jack to increase the gap to an acceptable width.

The remaining parts of the chassis that needed to be fitted at this point were the chain roller mounts, headrest mount, fairing mounts and steering arms.

Figure 5 Chassis ready for fitting of chain rollers, steering arms and the shaft for the moveable seat headrest

Figure 6 Front roller mounted in position

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The adjustable head rest was new for us but not difficult to make. I opted for a quick release setup using a standard bicycle quick release. All that was needed was a tube drilled, bored and turned to the correct diameters then welded on at the correct angle (parallel to the seat).

Since we were inexperienced in composites we were faced with a choice of either building our fairing/bodywork from core flute or purchasing a professionally made composite fairing. It was decided early on to purchase a fairing as we needed to make sure the measurements suited our chassis. We looked at a number of options before deciding on one that had been developed earlier in 2013 for another racing team. This particular design had been developed from a previous one built for the Wonthaggi 24 hour race in March. It debuted in a 6 hour race in Adelaide and performed well by all accounts of the team using it. The builder was a friend of our team manager based in Ballarat. He was happy to build us a fairing from the moulds used for its predecessor. The Kevlar/Carbon composite was expected to weigh around 7kg, which is quite light considering it incorporates rollover and side protection. It was also quite low which suited our chassis design.

At this stage the fairing was about 2 weeks away and we needed to wait for its arrival to determine the placement of the fairing mounts and steering arms. This left us with only the seat left to construct. The seat was to be defined in width by the chassis sides and height (from ground) by the chain. We allowed for 20mm clearance above the chain and set about making a core flute template to help visualize how the aluminium seat would be shaped.

Figure 7 Adjustable head rest, a new concept for us

Figure 8 Core flute seat template fitted on chassis

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The original plan was to have angled sides that rose from the flat seat base up to the chassis where it would be attached. We were also planning on mounting it to the lower chassis tubes. However, once we did this with the core flute, we realised that it would be virtually impossible to remove the seat with ease in the event of a mid race issue with the chain or rollers. So it was decided that we would only attach it to the top tubes and use vertical sides for simplicity and ease of removal. It would be attached by rolling the aluminium over the sides of the chromoly.

The following week I was able to make the seat. After cutting the sheet to size and folding the sides as well as the centre fold, I was able to place it into the chassis to determine the final cuts. I then TIG welded the sides to give the seat its final shape. We then returned it to the chassis to fold the sides and rear over the chassis members. Holes for spine and fluid drainage were cut later as well as holes around the steering arms and seat belt bolts which were fitted soon after.

The following week the fairing had arrived. It came in 3 pieces. It was delivered as a top and a bottom half, as well as the canopy/door that attaches to the roof. In order to prepare it we needed to cut out holes for the wheels, windscreen and windows as well as trim the sides and attach top and bottom.

Figure 9 Chassis with the finished seat and steering arms fitted

Figure 10 Chassis sitting in lower half of the fairing 7

We also needed to place mounts on the chassis at appropriate places. We decided that the most convenient places for mounts would be at the ends of the cross member near the shoulders, below the middle cross member under the seat, two up the front where there are rigid sections in the fairing and above either front wheel attached to the knee rollbar within the fairing. We also noticed that the head rollbar incorporated in the fairing was not continuous, so we needed an additional mount there to properly connect the rollbar.

The intended method of joining the two halves is to apply carbon fibre to the inside. An issue with our previous vehicle was that it was difficult to remove the chassis for modifications and servicing in between races. So we decided to join the halves as well as mount the chassis with bolts rather than carbon. This also is an easier option given our lack of experience with composites and our short time frame. As a result, our mounts consisted of tubes with flat plates welded on the ends, each with 2 6mm bolt holes. At this point we had 3 weekends to work before the race, so we set about making the mounts. Most of the mounts were completed that weekend; however we had a shortage of chromoly so we bought another length during the week to finish off the chassis. The bolts for attachment required washers to be made. We kept these as thin as possible and used bolts with tapered heads to limit their exposure as these are on the outside of the fairing and affect aerodynamics.

Once the mounts were attached we started to trim the fairing and cut windows, as well as fit the components to the chassis. Due to the substantially different front end of the chassis, the placement of the steering rods took a bit of thinking and testing. But we were able to find a setup where neither the tie rod nor side rods touched the chassis, by using larger spacers. The chain was also an issue. While the driving chain didn’t interfere, the return chain needed to pass under the lower cross member of the chassis and over the tie rod. The clearance at each point was minimal so we needed to attach plastic strips to prevent the chain from damaging the metal. The result was a slight chain slap when in low gear and bumpy sections of road which is not a problem at all. Another issue with having the seat so low was that the chain also has to be low and the return chain at the rear section would have scraped on the floor. This was prevented by running the chain through a tube to guide it. This also meant that the chain was pulled at a lateral angle when in a low gear; however the effect of this is minimal especially considering the little time spent in the lower gears in our form of racing.

Figure 11 Close shots of the steering and roller setup 8

Figure 13 The complete rolling chassis with all components fitted

Figure 12 The base of the fairing while being mounted. Bolts are visible beside the wheel.

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Vehicle Specifications

Wheelbase: 1220 mm Track Width: 630 mm Weight: 30 kg approx Overall

Height: 680 mm Length: 2650 mm

Seat Angle: 20 degrees Chassis: 4130 Chromoly Steel, 19x0.9mm, 25.4x1.1mm, 12x0.9mm Fairing: Kevlar-Carbon Hybrid Components: 16”wheels 10 speed cassette 11-26T 80T chainring Sturmey Archer front drum brakes (independent)

Figure 14 Final product post race.

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Post-race review Generally, the vehicle was success. We had no rollovers and didn’t even lift a wheel off the ground in any normal cornering situations. Rider reviews were all positive with handling, acceleration and straight line speed all at or above expectations. Things to work on for the next race are remaking the front axles (see below), improving the seat comfort and resolving issues with fogging. The seat can be improved by cutting further spine holes for shorter riders and adding an extra layer of foam on the bottom section of the seat as well as attaching it better with more glue and creating a rougher surface on the aluminium sheet. Fogging is caused during the night when the outside temperature drops well below the heat produced by the rider inside. It can be resolved by either double glazing the windscreen or improving air intake and outlets by running air up the screen similar to a cars demister. I was the first to experience severe fogging and was forced to pit and remove the screen during the night. Overall, the vehicle performance met and exceeded expectations, the chassis held together with no stress damage. Considering the race was effectively its first testing session, we were left with very few things to work on for the next race. Major incidents

• Spinout on very first lap (Friday night practise session) On marshal point 4 at the Murray Bridge circuit (a 90° right hand turn), another vehicle made contact with the inside tail of my vehicle. This, along with water on the road, caused me to spin 180° and stop next to the gutter. No damage was caused and it was promising that, despite the significant impact, all 3 wheels remained on the ground. This was a good sign of the improved stability of the new vehicle. Something that was later commented on by a number of riders.

• Faulty front axles The first major incident of the race occurred approximately 4 hours into the 24 hour race. The rider account was that he rode into the corner at marshal point 18 (commonly referred to as “crash corner”). There was no yellow warning flag out despite an overturned vehicle and marshals in the middle of the track. This obstacle forced him to swerve towards the right gutter which he hit, throwing the vehicle onto its left wheel. At this point the left front axle bent substantially, locking up the drum brake. The lock up was so severe that the arm that attaches the brake backing plate to the kingpin was ripped off and after colliding with the chassis, the aluminium backing plate cracked. When removed, the plate shattered into 5 pieces. After retrieving the vehicle from the track it took us an hour to fix. We were forced to hammer the bend out of the axle, then after buying a new brake we needed to weld the arm back onto the kingpins before refitting the parts. After resolving the issue and returning to the track we needed to determine the cause of the failure. After talking to the rider it was clear that the axle had failed under the added load when the right wheel left the ground.

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Our suspicions were confirmed when the right axle suffered a similar fate later in the race. This time it seemed that a spoon drain was the cause. When taking the spoon drain at an angle close to parallel, the weight shifts to the right wheel. In this case that weight shift was too much and once again the axle bent, locking up the wheel and snapping the brake off. It was less severe this time and we were able to salvage the brake. It took us 30 mins to straighten the axle and re-weld the attaching arm. It was clear by this point that something was wrong with the axles as they were failing under loads that they should easily be able to handle. We decided that they must have been mild steel rather than high tensile due to some mistake while machining them. While the easy fix for the next race was to remake them out of the correct material, we still needed to finish the race. So the riders were instructed to take the spoon drain at a more direct angel. This instruction was followed and proved successful and we made it through the rest of the race with no further incidents other than a flat tyre.

Concluding remarks from Murray Bridge race The chassis was successful. As mentioned above, the handling and stability was exceptional. The stiffness of the triangulated structure as well as a solid seat allowed for improved acceleration. Most further improvements would be to the fairing. Increasing foot clearance and decreasing width are the main points to work on. This is the limitation of buying a fairing that is not designed specifically for the chassis it is fitted to. The fairing height was almost perfect for our chassis however. Other major improvements for future races will be to the seats comfort and reduction of fogging as detailed above. Observations from the vehicles 2nd race at the 2014 Wonthaggi HPV GP

Figure 15 Wonthaggi Race Circuit 12

The vehicle was prepared for its second race by making minor changes to the windscreen configuration to reduce fogging and allow more foot room, both being successful. The faulty axles had also been discarded and replaced with ones made from 40 tonne high tensile steel as originally planned. This removed all of our mechanical issues from the previous race. The Wonthaggi circuit is one of the tightest circuits used in HPV racing, considerable tighter than the Murray Bridge circuit. It features an S-bend including a 180 degree turn as well a number of 90 degree or more turns that often see rollovers and crashes. My first thoughts while riding were that my lap times were faster than the previous year but I was also using the brakes less. Previously the tight corners had required very heavy braking to reach an appropriate speed, however only light braking was required in this vehicle as cornering speeds were significantly higher. This made it easier to overtake on corner exits and mid turn. There was no under steer or over steer, the handling I experienced was the best I had seen I my 9 years of racing. The only times I lifted a wheel off the ground was when veering off the desired race line while navigating traffic on tight corners such as corner 1. Other riders had similar comments. One rider who has experienced a number crashes in the past while navigating slower traffic had no difficulty avoiding crashes in this vehicle. We completed the race without an incident and there is very little work required to prepare the vehicle for the next race. We won’t even need to repaint it. Concluding remarks It is quite clear that lowering the centre of mass has had the desired effect. I raced in many different vehicles while at high school. We had a number of 4 wheel vehicles that were designed in the late 90’s for stability at the Maryborough race circuit. At the time it had a tight 90 degree turn at the bottom of the hill which required heavy braking to avoid rolling over (the race now runs in the reverse direction). In my final years at school we were building partial space frame designs with a longer wheelbase (around 1300mm compared to <1200mm). The idea of these was to recreate the stability of the 4 wheelers by putting more weight on the back wheel and not having the complicated dual wheel drive system and added weight of 4 wheels. I also built a training vehicle at that time of the same design. These vehicles were successful; however the earlier ones had some understeer. My design was essentially following on from these vehicles by moving to a full space frame in order to lower the centre of mass and provide a stiffer frame. The handling and stability of this vehicle exceeded that of the 4 wheel vehicles I have raced. It also did this without the added weight or loss of aerodynamics (due to a wider rear end). Last Updated Wednesday, 16 April 2014

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