Overview:
Welcome
Pre-launch technical meeting – Wednesday, January 23 (location TBA)
2008 Race Date – June 14
Things we’ve been working on over the winter
2007 Wrap-up report (attached)

Welcome:
YES – it’s that time of year… time to dust off the rules of gravity and start trying to use them for our advantage – it’s Canary Derby Time! I hope you had a happy New Year’s and holiday season. If you’ve been fretting about the extra holiday poundage you may have acquired… just think – it’ll make your entry in the 2008 Canary Derby go even faster… dieting is for slow people.

Pre-launch technical meeting – Wednesday, January 23 (location TBA):
We will officially ‘launch’ the race in the coming months, but I wanted to bring the technical brains behind last year’s race together to discuss plans for this year. I invite you to a pre-event meeting on Wednesday January 23rd from 5pm to 7pm… (No location confirmed just yet – details to follow) There will be a formal agenda circulated to cover the first hour and the second hour will be brain storming and casual conversation. I know everyone’s busy – so if you can drop in at any time it would be great to see you.

First and foremost, I want to hear from you about what worked and what didn’t… AND – what you think was missing that we can add this year. As we go into year 3, I think we have a good foundation (both technically and procedurally) and I hope we can push forward to do things more efficiently – and make sure everyone has the very best time possible.

2008 Race date – June 14:
This year the race will be held on Saturday June 14. The practice day will likely be held on May 31st. Depending on the ramps and volunteers, we might even do an additional an earlier test day as well.

Things we’ve been working on over the winter:
No… the off-season wasn’t all about turkey and football (what happened to my Dolphins?!?!). There have been some discussions about things to add / change / improve for this coming year… Here are some thought starters.

§ A new ramp set up
§ I want to investigate a “Fun category” that would emphasize creativity / innovation / and fun.
§ Race volunteers from race teams
§ A start area BBQ for team members
§ Car building blog / wiki – better web presence for car builders
§ Improve the process of getting cars up to the top of the track
§ Continue to develop the Archipelago Timing System
§ Improving the movement of cars between the pits and the ramp

If you want the details of these thoughts… come to the meeting. J

cheers!

s

I  will post the official times when I get a hold of them, and some pictures.

There was a radar gun on the course but I didn’t record the speeds. Off hand I think the maximum speed at the corner was around 37-39 kph, not really much different than last year, I was expecting someone to hit 40. I do know that Schneider Electric had the fastest radar speed. I think there are about half a dozen cars behind Schneider in a tight pack.

Our car ran unpainted and without bottom or axle fairings. I estimated that the un-faired portion of the total car frontal area was around 25%. Putting those fairings on *should* make the car faster. We also ran without wheel discs (we are using the heat shrink mylar wheel cover technique). Our wheels are larger than the ones we used last year, longer spokes, more air resistance.

Here a few pics of some of the cars… we didn’t get any pics of Carmanah’s car, but if you want to get an idea of what it looks like just glance at the blog’s masthead, ie last year’s Aspreva car (dig-dig).

Someone said to me that you’re not a real builder unless your working on your car late into the night before the race.

I hope to post pictures and commentary of practice day.

2007-canary-derby-pit-lane-assignments.pdf

(poll linked on blogroll)

lets see if we can generate odds

See here for an interesting discussion on bearings.

Seeing as it is only 2 weeks from the practice day, and seeing as we were all having a drink, the details of our car designs started to dribble out. Different approaches, from low profile to high. By the way, if anyone would like a custom made water tunnel as seen in that linked article, drop me a line.

Here are some early construction pics of our (Aspreva) car. You can see the pan view is a symmetric airfoil shape. A curved fiberglass fairing will cover the top and bottom plywood “plates”. The driver is totally within the car, looking out front through clear Lexan front (the open areas).

Its about 112″ long, max width 19″, height as shown is 19″, but body will be higher by about 4 inches when top and bottom fairing applied. Wheels are 27″/700c, road rims with mountain bike hubs (20mm axle), discs on rear wheels (Avid BB5), moderate tires (28 mm Panaracer).

Fairfield Bicycles – Richard and Max helped with the wheels and brakes, and with great technical advice. I think they are the best bike shop in Victoria.

University of Victoria – chemistry and physics machine shops – thanks to JP & DS for advice, and especially JP for the works of art (custom stub axles).

Metals Supermarket – big thanks again this year to Mark for metal supplies.

Slegg Lumber – thanks to the Sooke outlet, for the plywood.

Acura Plastics – a discovery for me, good tech advice and plastics source.

West Marine – Sidney store – helped with epoxy resins and fiberglass cloth.

Was looking for 3/8″ UNF lefthanded thread nuts. Tried major fastener outlets, tool and equipment supply place, and a big hardware store. Nope, might as well be asking for a muffler valve.

Ended up borrowing a tap from secret source.

Tip: if you have to make your own 3/8″ nut, UNC or UNF, left or righthand thread, take a 5/16″ nut and drill the threads out with a  5/16″ drill. This gives a pretty good hole for a 3/8″ tap.

Remember to use cutting oil and back off every part turn to clear the chips.

The Collingwood Street Fresh Choice Trolley Derby

The New Zealand Trolley Derby

-axle alignment

-accounting for any flex in chassis, or eliminating flex

-provisions for axle adjustments

Our car is designed so that the axles are a sub-assembly of the main chassis. Other car designs may have the axles and mounts as integral with the chassis – so the above points may have been taken care of already.

My approach in axle design differs slightly from what is outlined in the “soapbox construction manual” (linked in share box on sidebar) in that I am discounting the need to account for axle flex in the mounting system. There will be some flex in any system, but I theorise that with beefier axle members and pneumatic tires, road shock will be taken up mainly by the tires rather than the axle itself. If you are using solid tires and solid wheels then road shock will be translated almost entirely into axle flex.

Consistent with this approach is our goal to eliminate (or at least reduce) any chassis flex. As a side note, the photo of the Canamera/BC Cancer Agency car shows a very low ground clearance. I am sure the designers have done their homework on the shape and angles of the launch ramp and speed bumps, but it looks close to the limit before grounding out. In their case chassis flex would be quite unfavourable

Another thing I hate about styrofoam is how it seems to take a “set” when sanding. Hand sanding in one direction sets up the foam cell structure to rip when the sanding direction is changed. This often happens when you are doing the final touch ups.

Grrr.

As I carve away, I am thinking bad thoughts about those fortunate teams that have access to a 3 axis CNC router – you know who you are.

Also notice the penalty of having a higher centre of gravity (second race).

(video’s owner does not allow embedding, so you have to click on link to watch on YouTube site)

link

Wonder how many bulders out there have their cars built, ours (Aspreva) not finished, but hey, one month to go!

-total of 21 teams entered
-some of the new teams at meeting, very enthusiastic.
-Camosun College entering team, they have extensive fabrication facilities (grrr)

-finish line will be crosswalk out back, out of bounds (ie stop car before) will be speed bump further on (over 200 feet).
-race day will be busy, approx 65 races in total. Will be a challenge to turn cars around and back up hill in short time.
-they need volunteers desperately!!
-race teams supply crew at finish to load car
-entire team must sign release, only team members in pit area
-drivers sign release too and must be there early (9am or before) to have meeting with director
-drivers will be weighed and given wrist band with weight and ID to wear.
-we won’t be carrying cars up to start via stairs, have to push car around the “long way” (you know what i mean).
-it will be much better organised as to calling cars for race etc.
-each car gets at least 4 runs, 2 in morning, 2 in afternoon.
-best total times (inside and outside lanes) is what counts (like last year)
-radar gun will be positioned at corner, so will get speed to, and away from corner.

The race director has stated that there will be a time penalty imposed on cars that do not stop within some distance past the finish line. This distance has not been set, but 150 feet has been hinted at.

Update (April 25): The Race Director has just sent out mailing stating at least a 200 foot distance.

I’ve created a very simple spreadsheet calculating braking distance at various speeds and braking forces. WordPress doesn’t allow me to link the Excel file to the blog, but if you ask in the comments I can email it to you.

Update (April 25): WordPress now has new widget allowing more file formats to be shared, see the sidebar and you can download the spreadsheet.

The spreadsheet allows you to enter various car weights, velocities and braking forces. The car mass and velocities are straightforward enough, but how does one easily measure the retarding force generated by the brake system?

One way is to have the driver in the car, applying the brakes, while others try and push or pull the car. Measuring the force applied via a spring scale or the like will give you a pound or kg force number that you can enter into the spreadsheet.

Another way is to have the car on an incline, and if the brakes hold, then you have a fair idea if the brakes will stop the car within 150 feet.

Let’s assume the car can just hold itself on the 15 degree incline of the starting ramp. The “downramp” force component can be calculated by:

(note: max, car mass used, 375 lbs or 156 kg)

force = mass * sin(ramp angle)*(accel. gravity)

= (156 kg )*(0.2588) *( 9.8m/s^2)

= 395.7 Newtons or 40.35 kg-force.

Plug that into my spreadsheet, and at a velocity 55 kph the car would take a distance of 151 feet to stop.

I can imagine using some plywood to make a ramp at a steeper angle to determine the braking limit. It doesn’t matter if the tires skid or the brakes don’t hold, either one will indicate the limit. Measure the angle and then calculate the force. Its a handy estimate to see if you are at least in the ballpark.

I only hope I have got the angle/force formula correct, its been while since I have had to do trig. Oh and another thing, this estimate method does not, obviously, take into consideration any braking force generated by air or rolling resistance.

Cart type has the advantage of simplicity. The axle is controlled by cables attached outboard and either to a pulley and wheel control for driver or just 2 cables with handles (see soapbox derby construction manual). Two main disadvantages: the wheels will scrub more the tighter the corner turned. Maybe its not a big negative on the Canary Derby course, I think the tire scrub is really only a factor in turns less than 180′ radius (that radius comes straight out of my butt, can’t reference it). But the other negative is the effect that applying front brakes (if used) would have on steering. Most likely the brakes would not apply perfectly evenly to both wheels at the same time, resulting in a steering effect. This would be a problem if you had to brake suddenly. Similarly bumps on the road can have the same effect. A lesser disadvantage is that cart type steering does not provide any steering “feel” or self-centering.

Kingpin type steering has geometry that if set up correctly, provides steering “feel”, self centering, no bump or brake steer, and little if no tire scrub on corners. Its the type of steering used in cars. The kingpins are connected by a cunning arrangement of pivots and connecting rods, either to a steering box (rack and pinion often) or to steering “levers”. This type of steering is more complicated to construct and its debatable if it really has a big advantage over axle steering on the Canary course. Some cars last year did have it, looking totally cool and got a lot of compliments, two bonuses in my book. Have a look at the steering links on the side, and also Google for “Ackermann steering” for more info.

And a couple more points…

If you decide on the cart type steering, remember to install some sort of limit to the amount of travel the axle can make. Otherwise there is a possibility of major over steer (again, see soapbox derby construction manual).

Here is a good site: Analytic Cycling “provides technical methods for evaluating and estimating cycling performance and parameters. It makes extensive use of differential equations and advanced numerical methods”.

1. True them, or get a bike shop to do it. Remove hop and wobble.

2. If hub uses the old cone type bearing races, wash out grease and use oil for lubrication, then adjust them.

3. Research tire choice. hey, I’m just sayin’….

4. Psst… some say a little talc on inner tube makes the tire run faster.

5. Consider wheel covers. I think we were the only team to cover our spokes last year, (wrongo, Ed.). I bet more will do it this year. Its a no-brainer.

6. Wheel alignment – they all have to be pointed in the same direction. Setting aside steering complications, all four wheel’s axles should be perpendicular to the car’s centerline. Here is a simple set-up to check alignment (and also allows toe-in measurement, if you want).

Find a nice flat working area, concrete floor garage is good. Strike a line on the floor, this will be an important reference line. Rest the car on some supports so that the wheels are off the ground (no need, Ed.). Align the center point marks on the car (didn’t I mention you should transfer that construction centerline to the outside of the car at some point?) directly over the reference line on the floor. You can use a plumb bob for that. Now string some fishing line between between jack stands or similar heavy objects, see the diagram. You want the fishing lines to be equal distance from the centerline, and parallel. Also the line should be axle height.

Now using a machinist’s ruler, you can measure from the wheel rim to the fishing line. Measure from two points on each rim, 180 degrees apart, ie 9 o’clock and 3 o’clock. The two measurements should be the same if the plane of the rim is parallel to the centerline of the car (assuming rim is not bent).

Well that pretty well covers the obvious, I’m not going to say anymore about wheels. Esoteric discussions will have to wait until after the race.

Using, as we did last year, a chassis base of 3/4″ baltic birch plywood, gives you a good foundation onto which you can attach the mechanicals. For axle to base attachment, we used one of the methods shown in soapbox derby construction manual. The plywood base itself is not a stiff enough structure for a good racer, but with the sides attached the structure is very stiff (in essence a monocoque).

Remember to draw an accurate centre-line on the base, very important for accurate alignment of axles.

The picture below is of the car mostly assembled but not painted. You can see the foam nose (glassed over) and the extra bit of side material scabbed in. The plywood bottom was 96″ long, because the sides curve, an extra bit of 1/8″ ply is needed. The foam nose brings the overall length to 100″ (which was the max last year).

The blue top is simply 2″ foam, carved to shape and then glassed over. Obvious to point out here that polyester resin would melt the polystyrene foam, you have to use epoxy.

Bearing friction on bike wheels is pretty darned low. To get to that better happy place, try replacing the grease with oil, use high quality ball bearings (do caged bearings really have lower friction than loose ones?), adjust the cones, and if using cartridge bearings, cut away the rubber water seal.

The rolling resistance (this discussion limited to rubber tires on asphalt) is also affected by tire pressure and tire tread pattern. Higher pressures = lower rolling resistance. Another caveat, maybe “too” high a pressure will result in a rougher ride and a loss of horizontal velocity. Perhaps there is a sweet spot in tire pressure, high enough to reduce rolling resistance, but not as high as to eliminate shock absorbing. No tread (slicks) are faster than treaded. Narrow tires faster than wide.

The cross-sectional shape of the wheel rim in a spoked wheel has a large effect on the air resistance of the wheel. A box section rim will have a higher resistance than a deeper and tear dropped shape rim. Fewer spokes will also mean less air resistance. Disc wheels, especially lenticular cross section ones, have the lowest air resistance (see links under “blogroll”) Look at time trial and triathalon bikes to see what the current thinking is. Do we all get the hints here?

Top of the line disc wheels or those fancy reduced spoke wheels are pretty expensive, and if bought new would blow the Canary budget limit. In my next post I will talk about inexpensive ways to make your wheels as fast as they can be.

I really would like other teams to comment and contribute. Yes its a race, and so we won’t share all our ideas, but in keeping with the purpose of the Canary Derby I think a bit of collaboration will help all of us, especially new teams.

Sometimes I imagine that this year all of the cars will look similar, a natural selection process (after all, the cars will be subjected to the same conditions). But then I remind myself that the people in the companies entering all have strong ideas and opinions as to what makes the best car.

I hope there will be a diversity of approaches, its much more interesting and fun that way.

So please, if you have any tips or resources you would like to share, let me know and I will publish them here.

Determine what position the driver is going assume in the car (head first not allowed). Have the driver assume that position and measure total height, width and length. Having the driver do that on a long bit of cardboard or paper allows you to scribble down the stats right on what you will be using as a template.

Now decide on shape, starting with plan view, that will enclose the measurements you just made. There are a couple of things to remember in this layout process:

1. reducing frontal area reduces drag
2. a fair curve is a fast curve (fair means smooth curve transitions)

Strike a centreline down the length of the cardboard/paper template. Lay out the measurements from that centreline, but only do one half, as if car was sliced longways down middle. Then draw the plan shape on one half. You can use a long bit of 1 x 2 wood as a batten to spring a nice curve.

You then can fold along the centreline and cut out the template to make a symmetrical pattern. A plan view outline of the car.

An elevation view follows more or less the same procedure. But here you have to decide how much of the driver will be sticking out of the car, will there be a canopy etc? Just remember that reducing frontal area will reduce aerodynamic drag (its a mantra I will repeat often). Also consider hand placement for steering, knee and foot room, and ingress/egress.

The plan view template is useful even if you are making up a welded tube type car. It allows you to experiment with the placement of axles, steering gear, back rests, ballast points etc. For me its more “real” than using Autocad or Solidworks or even hand draughting. You can make cut outs of component profiles and place them on the template, have the driver on it, move positions, see what works and what doesn’t (interference issues do arise) before cutting building materials.