Post-Race Feedback, please!

[2016_Eagle_Dad]

Looking for feedback after this season's race.

My son is a Tiger and this was the first PWD car I've built since I was in scouts as a kid. I am not any kind of tradesman but consider myself fairly handy with most tools. I let my son design the body and paint scheme, even let him do the sanding...but once it came to wheel/axle prep and install, I handled that part. I also decided on weight placement but explained everything to my boy as we went along. He was always with me whenever work was done.

Even though this was our first car, I was feeling confident he would at least place in the top three, however, he was consistently 3rd out of 3 on the track and came in 6th out of the 6 Tigers.

Here's everything we did to the car:
1. Body shape was based on a muscle car, long hood followed by angled "windshield", followed by another angle to the trunk area and a final small bump for a spoiler. Something like this: \_/--\___
2. We drilled a horizontal hole through the cab area, as high as possible and about an inch in front of the rear axle and inserted round tungsten weights (purchased from Hobby Lobby). These were glued into place and we used sawdust/glue to cover the holes.
***At this point (with wheels and axles) the car was 5.0oz based on my electronic kitchen scale***
3. I used the Derby Worx Pro rail rider tool to flatten the axle heads, remove the burr under the head, and bend the axles to 1.5 for the front two, 2.5 for the back. I made sure to use a sharpie to mark the head so I would know which way the axle was bent afterwards (marked front and rear differently as well).
4. I then placed each axle in my drill and first used a white ceramic rod to smooth it out followed by 600 and 2000 grit wet sandpaper.
5. I used a straight razor to run against the wheels, chocked into my drill, to ensure they had a flat surface. This was the only iffy part because I didn't have the tool but didn't end up removing too much material.
6. Paired up axles to wheels applying graphite liberally inside the axle hole, the axle itself, and the space outside the wheel where the axle head meets the wheel. Afterwards, I would flick the wheel and made sure each would spin for roughly 20s before committing to the pair.
7. Used the Pinewood Derby PRO Axle Inserter Guide Tool to install the axles on the car.
8. At this point I wanted to achieve a "Rail Rider" so I replicated the incline/painters tape method in this video: https://youtu.be/P11Bdkxhlg0?si=VWYgt5eOg8cZbENI&t=94
We got the car to drift to the right about an inch over four feet. The front right wheel also was not exactly touching the ground enough to have traction but wasn't lifted so high that it was noticeable.

On race day, we applied more graphite and spun the wheels many times to ensure it was applied all over. At registration, their scale showed our car at 5.2 ounces...despite the kitchen scale confirming 5.0 before we left our house that morning. I even took a picture of it. Another parent brought a tool bag so I drilled out enough of the bottom of the car for their scale to show 5.0. I tried to remove wood in the center and front-end of the car, in front of the weights. I didn't have the opportunity to sand the bottom of the car and was worried about sawdust getting into the axles but even with drilling, I blew out each axle to be sure and again...added more graphite. Nothing was hanging down post-drilling.

Here are my initial thoughts:
1. Make sure our scale shows 4.8oz before leaving the house next year.
2. Go with the boring/basic wedge shape (I know some will say this isn't super important).
3. Apply polishing compound after 2000 grit sandpaper, maybe even use 3000
4. Either no bend on the axles or the same bend degree all around.

So, based on all of this...what could I have done differently? I am definitely salty about not benefiting from the work/time we put into the car but I want to learn from mistakes and do better next year. I didn't like seeing my son deflated and let down.

[exoray]

It's really hard to say why you placed 6th, maybe all those other cars were just tuned that much better, or maybe there was an issue with your car that went unnoticed... What was the time spread between the top three cars and yours? This will give some indication if the others were just tuned that much better or if you possibly had an issue...

As for weight, it's always tricky as these cheap kitchen scales are not all that accurate, you should have a plan to bring it up to 5.0 on race day... That can be adding some extra weight at check in or removing weight... Generally unless you invest in some of the weighted sticky clay, I find it easier to just bring a cordless drill and a larger drill bit, for me I generally chuck up an Ebay Chinese Forstner bit (8-20mm) to remove weight if needed and will lend it out to others if they need it... The Forstner bits don't bite and pull in like twist drills do so less chance of excess removal and/or damage to the car... One way to see if it was your scale that was off or the race scale is go to the post office and ask them nicely to weigh your car, around me almost all the post offices have 24/7 kiosk now so you can do it anytime and not bug anyone... I say this because if you weigh in at 4.8 on your scale and it's the accurate one and next year you show up at the race and they are using a different scale you are back to square one... Not that arguing your scale is accurate and theirs isn't will get you anywhere, but it's nice to know if your scale is accurate just the same and always build to 5.0 and then adjust at weigh in...

IMO if you did all you did and still came in 6th in a Tiger level race one of two things applies... Your car has a flaw that went unnoticed (like a wheel binding or rubbing) or all those other cars were dad cars that were fine-tuned...

[2016_Eagle_Dad]

I appreciate the insight, I like the idea of being prepared to add or remove weights on the day of the race. I will be sure to calibrate my scale using a known weight of some kind in the future too.

Also thanks for confirming that I did everything "right" and that I am not missing something obvious. It was definitely a fun day for him and hopefully a learning process for us both.

[Vitamin K]

Just some thoughts off the top of my head...

The first time I tried making rail riders, I'm pretty sure that I made them slower. You really need a way to verify that the rears are properly aligned, and a roll test like shown in the video can hide some of this because you are trying to test 3 wheels at once. Also, I don't have equal bend on all our axles. The rears get 3 degrees (from our jig) and the DFW we give around 7 degrees.

If you're running graphite, I don't think it's worth polishing past 2000 grit.

I've pretty much given up trying to improve wheels without a lathe. Rather than mess with wheel shaving or anything like that, better to build or buy a runout guide and some extra sets of wheels and use the best of the batch.

Big big agree on always making sure your final few tenths of an oz are done with removable weights. So much easier to pluck off trim weights than try to drill out the bottom of the car at check-in.

[FatSebastian]

Your car has a flaw that went unnoticed (like a wheel binding or rubbing)...

A few more thoughts...

1. Did you narrow the block or sand the sides down at all in your design? If your block isn't a full 1.75" wide where the nails insert, then the wheels can drag against the rail. I've seen this happen to first-timers.
2. How did you check that your bent rear axles were correctly aligned?
3. How did the car behave on the track? Did it bounce around or wiggle? It doesn't sound like your weighting was extremely aft, but...
4. You said the wheels spun freely with a finger test before the race. Did they spin freely afterward? Sometimes during handling the axles can be pushed in and pinch a wheel...

[2016_Eagle_Dad]

Deleted and replied in thread

[2016_Eagle_Dad]

Just some thoughts off the top of my head...

The first time I tried making rail riders, I'm pretty sure that I made them slower. You really need a way to verify that the rears are properly aligned, and a roll test like shown in the video can hide some of this because you are trying to test 3 wheels at once. Also, I don't have equal bend on all our axles. The rears get 3 degrees (from our jig) and the DFW we give around 7 degrees.

If you're running graphite, I don't think it's worth polishing past 2000 grit.

I've pretty much given up trying to improve wheels without a lathe. Rather than mess with wheel shaving or anything like that, better to build or buy a runout guide and some extra sets of wheels and use the best of the batch.

Big big agree on always making sure your final few tenths of an oz are done with removable weights. So much easier to pluck off trim weights than try to drill out the bottom of the car at check-in.

So you recommend adjusting the wheels so that it runs a straight rather than riding the rail? In hindsight this probably was the culprit. The car was painfully slow. Like, I probably wouldn’t have posted here if the races were closer or our car wasn’t dead last every time.

What jig do you use for axle bending?

Definitely a hard lesson learned on removable weights next time around. Thankfully an easy and non-catastrophic fix.

[2016_Eagle_Dad]

Your car has a flaw that went unnoticed (like a wheel binding or rubbing)...

A few more thoughts...

1. Did you narrow the block or sand the sides down at all in your design? If your block isn't a full 1.75" wide where the nails insert, then the wheels can drag against the rail. I've seen this happen to first-timers.
2. How did you check that your bent rear axles were correctly aligned?
3. How did the car behave on the track? Did it bounce around or wiggle? It doesn't sound like your weighting was extremely aft, but...
4. You said the wheels spun freely with a finger test before the race. Did they spin freely afterward? Sometimes during handling the axles can be pushed in and pinch a wheel...

Once the axles were dialed in for optimal drift for rail riding I superglued them in place. The wheels did spin freely. I used the Pro tool for spacing between the wheel and body. Also did not slim the sides down. Maybe 1 or 2mm came off in sanding.

[Vitamin K]

Just some thoughts off the top of my head...

The first time I tried making rail riders, I'm pretty sure that I made them slower. You really need a way to verify that the rears are properly aligned, and a roll test like shown in the video can hide some of this because you are trying to test 3 wheels at once. Also, I don't have equal bend on all our axles. The rears get 3 degrees (from our jig) and the DFW we give around 7 degrees.

If you're running graphite, I don't think it's worth polishing past 2000 grit.

I've pretty much given up trying to improve wheels without a lathe. Rather than mess with wheel shaving or anything like that, better to build or buy a runout guide and some extra sets of wheels and use the best of the batch.

Big big agree on always making sure your final few tenths of an oz are done with removable weights. So much easier to pluck off trim weights than try to drill out the bottom of the car at check-in.

So you recommend adjusting the wheels so that it runs a straight rather than riding the rail? In hindsight this probably was the culprit. The car was painfully slow. Like, I probably wouldn’t have posted here if the races were closer or our car wasn’t dead last every time.

What jig do you use for axle bending?

Definitely a hard lesson learned on removable weights next time around. Thankfully an easy and non-catastrophic fix.

We will always build rail riders if the rules permit (and if the track has a center rail). That said, for a rail guided car, it is imperative that the rear wheels be perfectly parallel with each other, otherwise they will either pull the car one direction or another, or they will fight against each other (or both). We usually (because of ease of construction) run straight rear axles and drill our rears at 3 degrees, using one of Microbrush's clear drill jigs to drill the rear axle holes. That said, I've also built cars with bent rear axles, using Stan Pope's bias weight system to align the bent rear axles.

I don't use any kind of jig for bending axles, just a piece of soft pine and a pair of pliers. I've written up my approach to the process.

[Loud2ns]

I think you should run the car slowly down a table with a yard stick to act as a "rail." Take notice if the rear wheel is dragging the rail. If it is, that could account for the slower speeds. We typically have to inset the body where the dfw is to keep that rear wheel off the rail.

Sent from my SM-G991U using Tapatalk

[exoray]

Like, I probably wouldn’t have posted here if the races were closer or our car wasn’t dead last every time.

If there was a huge gap in the finish times, then I repeat what I said there is an overlooked issue with the car... With the prep you did, the car should have been competitive at scout level races, you might not have placed in the top but it should not have been a blowout either...

I would say look over the car, get a flat surface and look at the wheels, since you used bent axels and your car was not a thin profile are the tops of the wheels rubbing the body in the rear when sitting on the flat surface? I have seen this on some cars, when holding the car and spinning the wheels with no downward weight the wheels spin freely, but when set down the extra play in the axle hub tolerance allows the wheel to [censored]/cant that much more right into the body of the car up top...

[2016_Eagle_Dad]

I think you should run the car slowly down a table with a yard stick to act as a "rail." Take notice if the rear wheel is dragging the rail. If it is, that could account for the slower speeds. We typically have to inset the body where the dfw is to keep that rear wheel off the rail.

Sent from my SM-G991U using Tapatalk

I’ll give that a try after I get the car back at this weeks meeting.

[2016_Eagle_Dad]

Like, I probably wouldn’t have posted here if the races were closer or our car wasn’t dead last every time.

If there was a huge gap in the finish times, then I repeat what I said there is an overlooked issue with the car... With the prep you did, the car should have been competitive at scout level races, you might not have placed in the top but it should not have been a blowout either...

I would say look over the car, get a flat surface and look at the wheels, since you used bent axels and your car was not a thin profile are the tops of the wheels rubbing the body in the rear when sitting on the flat surface? I have seen this on some cars, when holding the car and spinning the wheels with no downward weight the wheels spin freely, but when set down the extra play in the axle hub tolerance allows the wheel to [censored]/cant that much more right into the body of the car up top...

Yeah I will check that out when I get the car back at this weeks meeting. To the best of my knowledge the wheels had a big enough gap that it shouldn’t have rubbed.

[2016_Eagle_Dad]

Your car has a flaw that went unnoticed (like a wheel binding or rubbing)...

A few more thoughts...

1. Did you narrow the block or sand the sides down at all in your design? If your block isn't a full 1.75" wide where the nails insert, then the wheels can drag against the rail. I've seen this happen to first-timers.
2. How did you check that your bent rear axles were correctly aligned?
3. How did the car behave on the track? Did it bounce around or wiggle? It doesn't sound like your weighting was extremely aft, but...
4. You said the wheels spun freely with a finger test before the race. Did they spin freely afterward? Sometimes during handling the axles can be pushed in and pinch a wheel...

https://imgur.com/a/RoXL2nA

Here’s a video of one of the runs, we’re furthest from the lever (the black car that comes in 3rd)