Latest fab. project - downhill racer

[Jeff Ivers]

Surprisingly, some web research has turned up ceramic bearings for about $20 each in the size needed for the new wheels. I only need 8.

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[Jeff Ivers]

Bummer! I just got word that the downhill race scheduled for September 13 in Sand Springs, OK has been canceled this year due to "lack of entries"! I had already upgraded the car with new wire spoke wheels and semi-synthetic bearings (ceramic balls and metal races). I was working on beefing up the tie rods and brake pedal and adding a left foot rest. Oh well, as they say - "all dressed up and no place to go". Which bring me to the point of this post. Do any of you know of any other downhill races in the Midwest - preferably KS, AR, MO, TX, or OK? If so, please post up the info. I need to find a place for my grandson to play!

 

[Jeff Ivers]

2014 Modifications:

As I previously posted, the race for this year was cancelled due to lack of interest. I think it was more an issue of failure to advertise the event. Supposedly, the race will be back next year, so improvements are continuing, albeit at a slower pace.


New wheels with semi-synthetic bearings have been installed.



I have made and installed new, beefier tie rods based on 5/16 steel rod. (The old tie rods were cut down and became part of my swap meet cart).

Back in post #115, I showed how we had to cobble the brake linkage together to finish the race last year.



I had used 2 cable retainers from bike brake levers welded together and inserted into a homemade bracket to keep the cable pull straight as the lever moves. This is a couple of pictures of the failed components.



I found a 3/4" hasp to weld to the brake arm to take care of the pivoting function. I am still working on the fabrication of this part and will post more pics in a followup.

 

[Jeff Ivers]

My attempt to repair the brake pedal using a hasp (2nd iteration) failed. It turned out the pin in the hasp was a much smaller diameter than I thought and it broke with hand pressure after a couple of pushes.

So, it was on to the third iteration of the brake pedal design. This time I decided to use an old door hinge. I cut a slice out of the hinge that would act as the pivot and welded to it a piece of angle iron that I drilled and slotted to hold the brake cables. A piece of the hinge pin was cut and welded to the back side of the bottom of the pedal. I think I finally have a strong enough pedal assembly.

Side view of the pedal assembly as modified.


Top view of the installed pedal.


Side view of the installed pedal showing the connected cables.


I would have posted this update long ago, but developed a severe infection on my computer that necessitated reinstalling and upgrading the operating system and browser. Once that was done, I was blocked from uploading photos until I installed an alternate browser.

I am still looking for info on any other downhill races for 2015.

 

[Jeff Ivers]

Season 4 update - 5/21/2015

The great news is: the Great Sand springs Downhill Race is on! and scheduled for September 19, 2015. Sand Springs is a suburb of Tulsa, OK and held this event 6 years in a row up till last year when it was cancelled, allegedly due to lack of entries (personally, I think that was a cover story). The car is ready with beefier tie rods, beefier brake pedal cable linkage, left foot rest and wire spoke wheels with semi-synthetic bearings.

Any of you following this thread within driving distance of Tulsa are hereby challenged to build a car and bring your grandchild to race mine!

Also, If anyone is aware of any other downhill races in the central US, please post up a notice here.

 

[wasfast]

The ceramic bearings certainly don't hurt but the single biggest improvement will be rolling resistance, i.e. tires and tubes. I've raced road bicycles for a lifetime and researched the technical side a lot for Time Trial racing.

I'm guessing those are 20" wheels, correct me if that's wrong. There aren't a whole lot of choices for that size in tires but recumbents use them so there should be some faster options there.

Rolling resistance is a composite of the ply construction, tread type, weight and tube type. The goal is a more compliant system, not a stiff system.

You'll see tires listed by tpi (threads per inch). Higher is better.
Smooth tread will be better than deep patterned tread. High mileage/durable treads = harder rubber=bad for rolling resistance.
Lighter weight means a more compliant tire in general.
Butyl tubes are slower than latex although I don't know if there are latex tubes for this size. Use lighter tubes if you have a choice. Avoid puncture resistant/thorn resistant types. They just have thicker walls. Some options here:
http://www.schwalbetires.com/bike_tires/tubes/all

Avoid over-inflation (psi). Likely the best pressure is NOT the maximum listed on the sidewall. That's a listing for safety, not best performance.

This was the best I found on biketiresdirect.com was these continentals:

https://www.biketiresdirect.com/product/continental-grand-prix-20-inch

There's a Schwalbe Ultremo ZX tire in 20" (406mm and 451mm). Note that these are different sizes although listed for 20" in both cases. You'll need to research those to get the right size.

http://www.schwalbetires.com/bike_tires/racing_tires/ultremo_zx

 

[dowmace]

Season 4 update - 5/21/2015

The great news is: the Great Sand springs Downhill Race is on! and scheduled for September 19, 2015. Sand Springs is a suburb of Tulsa, OK and held this event 6 years in a row up till last year when it was cancelled, allegedly due to lack of entries (personally, I think that was a cover story). The car is ready with beefier tie rods, beefier brake pedal cable linkage, left foot rest and wire spoke wheels with semi-synthetic bearings.

Any of you following this thread within driving distance of Tulsa are hereby challenged to build a car and bring your grandchild to race mine!

Also, If anyone is aware of any other downhill races in the central US, please post up a notice here.

What's the age range? I'm in sapulpa and have a 7 and 9 year old.

 

[Jeff Ivers]

wasfast:


Thanks for posting the information on tires.

dowmace:

My grandson first raced at 6 years old. They have a youth class and an adult class. Your grandsons would be in youth class.

 

[Jeff Ivers]

The 7th annual Great Sand Springs (OK) Downhill race was held Saturday the 19th of September. My eldest grandson raced for the 4th year. The rules allow 200 pound weight limit per car NOT COUNTING THE DRIVER. They use a single elimination bracket and my grandson drew, for his first heat, the opponent who went on to win the race. The driver of that car was several years older, much taller, and quite a bit heavier.

My grandson is in the blue car on the left and led the race to a bit past the midpoint of the hill whereupon his opponent in the turquoise car overtook him and won by about a car length. The opponents car is extremely well built.

So now we are praying they continue the race for next year. Particularly since my youngest grandson has now decided he would like to compete next year.

And for me, it raises the question of whether I should attempt to build a second car.

 

[ScooterCO]

Um....? Yea, of course you should!

Shame he was eliminated in the first round but that's racing.

 

[justbummin1]

I have been telling my kids for a few years (one is 28 and the other 25) that I am NOT in a hurry to be a grandfather but now after reading through this, one of them better get busy because I need a little garage buddy again to build and play with.

 

[Jeff Ivers]

Um....? Yea, of course you should!

Shame he was eliminated in the first round but that's racing.

You are absolutely right - that is racing! The good news is he will be taller and heavier next year. Also, the car performed flawlessly - stronger brake linkage did the trick. And the bearings did improve performance. This year they did not use a starting ramp (15 degree ramp used in past). The car still hit 28 plus mph.

 

[TheEquineFencer]

Nice build. This is one thread that I actually went through and read most of it. My only suggestion is to install something I guess sort of like what a Kayaker uses the "seal" them inside a kayak to cut down on wind resistance getting inside the body and slowing it down.

Something else to check is the alignment of the rear axle to the front. I'd set two jackstands out front of the front axle. Tie a string to one and take it around the two rear tires and back up to the front to the other jackstand on the other side. Then adjust the jackstands L/R until the strings touch the rear tires from the front to the rear across the flat side of the tire. Do both jackstands the same and then measure from the string to the front tire to see how far off you are if any. Basically you have a "U" shaped string around the cart tires.

 

[Jeff Ivers]

Nice build. This is one thread that I actually went through and read most of it. My only suggestion is to install something I guess sort of like what a Kayaker uses the "seal" them inside a kayak to cut down on wind resistance getting inside the body and slowing it down.

Something else to check is the alignment of the rear axle to the front. I'd set two jackstands out front of the front axle. Tie a string to one and take it around the two rear tires and back up to the front to the other jackstand on the other side. Then adjust the jackstands L/R until the strings touch the rear tires from the front to the rear across the flat side of the tire. Do both jackstands the same and then measure from the string to the front tire to see how far off you are if any. Basically you have a "U" shaped string around the cart tires.

Good suggestion on the alignment - I did something similar to insure that both front and back wheels are tracking the same. I decided early on that I believed the small amount of wind resistance through the body was less important than weight, rolling resistance, and a fairly aerodynamic body - besides, I couldn't figure out a way to seal the openings around the axles caused by the way I chose to mount the body, particularly with the tie rods moving fore and aft as they go in and out.

 

[vintagespeed1956]

i really dig your project, always wanted to build one of those.

good luck in the next car build and this time add some caster (4-6*) so the thing goes straight without scrubbing speed with constant steering input "corrections". less height and lower CG might get 'er down the hill faster too.

 

[Jeff Ivers]

i really dig your project, always wanted to build one of those.

good luck in the next car build and this time add some caster (4-6*) so the thing goes straight without scrubbing speed with constant steering input "corrections". less height and lower CG might get 'er down the hill faster too.

To add caster, I would probably have to enlist the services of a machine shop or purchase spindles from some source - my home shop equipment and skills do not provide the accuracy of creating something with 4 or 6 degrees of slope on it. Anyone know where to purchase reasonably priced spindles? The CG is quite low now, well below the plane of the axles, as the extra weight and the seat are both mounted below the axle plane. Height and width will be reduced on a new car if I decide to build another. Some of the competition actually had steering racks installed on their cars. Anyone know of an inexpensive source for a suitable steering rack? So far, everything I have found is well over $100.

 

[TheEquineFencer]

I don't know if this is legal or feasible, what if you added a sliding weight. Then have some way to propel it forward suddenly so when it stops it Jerusalem the cart forward, sort of like if you were sitting still and wanted to make the cart move forward but "scooting" your body forward to move the cart.

 

[Jeff Ivers]

I don't know if this is legal or feasible, what if you added a sliding weight. Then have some way to propel it forward suddenly so when it stops it Jerusalem the cart forward, sort of like if you were sitting still and wanted to make the cart move forward but "scooting" your body forward to move the cart.

Great idea but unfortunately any mechanical assists to speed are prohibited.

 

[Jeff Ivers]

Season Five update!

Well, race fans, it is that time again. The next running of the Great Sand Springs Downhill Derby is scheduled for September 17 right here in the state of Oklahoma. This will be the fifth race for my oldest grandson and the debut of my youngest grandson. So, of course, that means it is time for grandad to get off his duff and make the car both ready and better for this year's race.

Before I get into the plans, though, first my personal invitation to all of you to come out and join in the fun. A google search on Sand Springs Downhill Race will allow you to find the registration site as well as info on past races. There are some interesting videos out there, as well.

For this year, since both grandsons will be driving the same car, I need to make the seat adjustable.


Currently the molded wood seat is bolted to a fixed bracket, which is then bolted into a fixed position.

A closer view of the bracket.

More of a side view of the bracket.

When I finish this post, it is out to the shop to finish cutting the last pieces of metal and start fabbing the adjustable mount.

From a performance point, this year I am looking into making wheel disks to make the wheels more aerodynamic. I did some google research and came across an idea using ABS plastic that I think looks real good. I am currently waiting on a call back from one of the local plastic shops concerning price and availability of the needed material.

 

[ilovevocs]

Good to see you back at! Look forward to following along.


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[no704]

For the stearing, you can buy dampers in different rates. Look like rear hatch struts. Many off road trucks add steering dampers. Check them out at McMaster.

 

[Jeff Ivers]

For the stearing, you can buy dampers in different rates. Look like rear hatch struts. Many off road trucks add steering dampers. Check them out at McMaster.

Thanks for the info, but why do you think I need a steering damper?

 

[Jeff Ivers]

Over the last few days, I have mostly fabbed the new adjustable seat frame.

This is a picture of the components in front of the original bracket with the seat setting on it.

This shows the welded up bracket with the sliding mechanism in the rear most position.

This shows the bracket with the sliding mechanism in a forward position.
I have alread drilled the mounting holes. Tomorrow, I have to devise the retention mechanism and then commence painting.

Today, I visited the local plastic shop and ordered 12 15.5 inch diameter pieces of 1/16" ABS plastic that will become wheel disks. That is the intended speed improvement for this year.

 

[no704]

coming off the starting ramp, sometimes the steering wheel would move a bit on him and he had a tendency to overcorrect, which negatively affected his run time. I am considering whether there is something I can do to help this situation for the future.

 

[Jeff Ivers]

coming off the starting ramp, sometimes the steering wheel would move a bit on him and he had a tendency to overcorrect, which negatively affected his run time. I am considering whether there is something I can do to help this situation for the future.

Ah, now I understand where you are coming from. My grandson had some trouble with that too, one year. However, last year they did not use the starting ramp. Have no idea if they will use a starting ramp this year. Do you compete at the Sand Springs race?

When it happened to my grandson, I think he was lined up in such a way that one wheel came off the ramp ahead of the other, naturally jerking the wheel in his hand. We tried to address the issue with coaching and I have to admit I haven't thought much about trying to devise a solution.

 

[Jeff Ivers]

With the race about 3 weeks away, I am finalizing the changes to the car.

This shows the stops I am using on the adjustable seat (to the left of the seat). No, I didn't devise some fancy push a lever and scoot the seat. This will be fast enough for a quick adjustment in the pits.

This shows the seat in place with the stops inserted with the seat in the rear most position.

I acquired 12 of these 15.5 inch abs disks (1/16 inch thick) with the center marked from the local plastic shop.

Drilled a 2 1/8 inch hole in the center of each disk. And then, took a nip out of each one.

Of course a nip is followed by a tuck to shape the disk to the wheel. I assembled one using duct tape on the back side to hold the tuck together, but then glued a strip to the back of the rest of them to hold them together.

Front and back.

Completed wheel.

Tomorrow, my daughter is bringing the grandsons up for a visit and the plan is to let them help assemble the other 5 wheels - smoothing the swarf, drilling mounting holes, and attaching the disks to the wheels.

 

[Vernon1969]

Looks like a good design and lite

 

[Jeff Ivers]

My daughter brought my grandsons up this past weekend and I was able to enlist their help to fabricate the wheel disks for the 4 wheels on the car and two spare wheels. Here is a pic of the car with them installed.

We took the car over to the church on the hill and let my youngest grandson get some familiarization runs in, as this will be his first year.
Next task is to create a dolly to lift the front of the car off the ground for towing behind the old fart cart. I hope to use it for that chore this year. If not we will rely on the 4-wheelers and golf carts that they always have present.

 

[Jeff Ivers]

With the race one week away, I have completed a tow dolly to engage the tow hook on the underside of the front of the car and raise the front wheels 3.5 inches off the ground so the car can be towed to the top of the hill without the driver having to steer. The plan is to use the old fart cart as the tow vehicle. Hope it has enough umph to haul me and pull the 200 pound car as well.

 

[Jeff Ivers]

Season Five finale!

Yesterday, the Great Sand Springs Downhill Derby was held (I think this was the eighth running, unless I lost count somewhere).

This year they ran double elimination brackets in both the novelty and competition classes. My oldest grandson won the Youth Novelty class.

This picture shows him in one of his heats and shows the aerodynamic wheels disks we added for this year. They were good for about 1 mph on peak speed, as this year he hit 30 mph for the first time.

This picture shows my youngest grandson who raced for the first time this year. This is one of his runs after he got past a case of nerves and kept his foot off the brake.

I chickened out on using my OFC as a tow vehicle, after getting to the site and walking the hill I would have to tow the racer up. It is much steeper (tho shorter) than the actual race course. I decided I did not have enough confidence to risk the hill towing a 200 pound racer with my 220 pounds on the cart.

However, the OFC is great for towing the racer back down to the barn for winter storage.

Next year, my youngest wants to also move up to the competition class, which means I may be building a second car. Also, the body on this one is showing the wear of several years racing and may need some work. If I build a second car, I think it may be time to engineer one that I can drive in the adult class and let the oldest grandson drive in youth. I believe the way to go will be a fixed seat and hand-operated brakes. Really want to try disk brakes on this one and rack & pinion steering.

So, now you know what I will be cogitating on this winter. Ideas and comments welcome.

 

[beakie]

re: aerodynamics
would be miniscule improvement in grand scheme, but maybe some "wings" to cover exposed rear axle and part of front axle. would clean up the look a bit too.

otherwise, this thread has me looking into local races for my boys (x3)... sadly it seems there are none.

edit

further research shows I'm actually minutes from Canada's only dedicated soap box derby track.

I may have a winter project!

 

[Jeff Ivers]

re: aerodynamics
would be miniscule improvement in grand scheme, but maybe some "wings" to cover exposed rear axle and part of front axle. would clean up the look a bit too.

otherwise, this thread has me looking into local races for my boys (x3)... sadly it seems there are none.

edit

further research shows I'm actually minutes from Canada's only dedicated soap box derby track.

I may have a winter project!

Go for it! I am envious - a dedicated track! I have recently heard there may be a race in the Kansas City area, but have not had time to research it.

Based on my personal experience, I think the most important factors to speed, in order, are weight, rolling resistance and then aerodynamics.

 

[Jeff Ivers]

Well, with both grandsons wanting to run the competition class, it looks like I need 2 cars for next year (and a way to get 2 cars on the trailer or a bigger trailer!)


While researching bike parts, I stumbled across the brake lever shown in the picture. It actuates two brake cables at the same time. I think this might be just the ticket for a second car - switch to hand operated brakes so the car can more easily accommodate different drivers (me in the adult class and my grandson in the youth class - yes, I think it is time to get in on the fun). I found the steering wheel at a swap meet yesterday for $10. I think it cleaned up pretty good, but forgot to take a before pic.

For the new car, I want to use disk brakes and would like to use a steering rack.

So far, I have not found a suitable rack for less than $100. Anyone have any tips for me?

With regard to brakes. I am still researching this issue and having some difficulty figuring out what I need. From a failure avoidance perspective, I want to stick with a .5" axle. I also want to use 20" bike wheels, but they must accept sealed bearings that will fit the axle. Where do I find wheels or wheel hubs that will accommodate disk brakes - remember, on a retiree budget?

Any help appreciated.

 

[chris_c]

http://www.ebay.com/itm/261854343226

This sort of thing looks ideal !

Or indeed any "Sand Rail" or Baja type steering rack !

 

[Jeff Ivers]

http://www.ebay.com/itm/261854343226

This sort of thing looks ideal !

Or indeed any "Sand Rail" or Baja type steering rack !

That's a great looking rack and would probably do a wonderful job - if it cost about 1/6 as much!

 

[chris_c]

http://www.ebay.com/itm/231912774138

Getting Cheaper ! !

 

[y'sguy]

Hmm, so I've lived in Tulsa all my life and as my wife will tell you I pretty much know everything. BUT, I've never heard of this race before!
I gotta get out more!
Congrats for all your hard work and a wonderful gift to have with your grandsons.
I have 3 grandaughters. 1,3 and 5 yrs of age-you sir, have got me thinking…

 

[Jeff Ivers]

Hmm, so I've lived in Tulsa all my life and as my wife will tell you I pretty much know everything. BUT, I've never heard of this race before!
I gotta get out more!
Congrats for all your hard work and a wonderful gift to have with your grandsons.
I have 3 grandaughters. 1,3 and 5 yrs of age-you sir, have got me thinking…

Yeah, I know what you mean. It is one of those events that if you don't see the newspaper on the right day or catch the right news broadcast, you will never know it exists. I didn't know about it till the 2nd or 3rd year. Google "sandsprings downhill race" for more info. Can I expect to see your out there next year?

 

[Jeff Ivers]

http://www.ebay.com/itm/231912774138

Getting Cheaper ! !

That is much better! I saw that ad yesterday and made an offer of $50, which they declined. Sometimes it is hard to know what something is really worth. I know how much I have invested in the first car and would like to get a second car built for the same or less money. Wish I could find a source of used parts, as I certainly don't need to pay the new premium.

 

[Pacha]

This is a great build, your grandsons must be very proud of you!!!
And this is a great site with a lot of great ideas that I keep stealing, thanks!!
Since you have only gravity power, the way to be faster is to reduce drag and resistance. Here some ideas to keep you grandsons in the first place:

I used to bicycle race and rolling resistance depended in a good deal on tire pressure, they are much higher than in car tires (between 60 to 100 psi).

Do you have to run 4 wheel?, using 1 in the rear tucked in the body will significantly reduce drag (like a can-am spyder).

Use a tonneau to cover most of the open cockpit with just enough open space you for you grandson.

Regards and keep posting!!