Weight and Distribution

[Cabrzama]

I am a complete novice at pinewood derby. Between my son and I we came up with a plan to add weights at race time, (based on the calibration of the scale at the race) using magnets. He/we built a pickup and in the bed glued four round magnets (looks like cargo). That takes our weight up to 4 oz. With the last 1 oz we are allowed, I picked up a bunch of different size bolts so that we can customize the weight as close to 5 oz at race time.

Is this a bad idea? Since I've already gone and done it, how should I distribute the weight of that final one oz in the bed--front, middle, back?

The big race is next week--it's our first, but I have two boys younger than my oldest so I have many races ahead of me.

[Darin McGrew]

I am a complete novice at pinewood derby. Between my son and I we came up with a plan to add weights at race time, (based on the calibration of the scale at the race) using magnets. He/we built a pickup and in the bed glued four round magnets (looks like cargo). That takes our weight up to 4 oz. With the last 1 oz we are allowed, I picked up a bunch of different size bolts so that we can customize the weight as close to 5 oz at race time.

Is this a bad idea?

The main problem I see is that the magnets may not hold the extra weights securely enough. It would be bad for your derby pickup to scatter random bits of hardware up and down the track. Or to dump its load at the finish.

Some derbies explicitly prohibit magnets. Others prohibit decorations/weights that aren't securely attached. You might want to check your derby's rules.

[Cabrzama]

Thanks for the tip--I will check with our coordinator. I think they will hold the bolts pretty securely. They have a very strong attraction--takes a bit of a tug to pull the bolts away from them. I think I worry more about the rules and distribution of them.

[Stan Pope]

Is this a bad idea? Since I've already gone and done it, how should I distribute the weight of that final one oz in the bed--front, middle, back?

Check carefully re use of magnets. Both with coordinator of local race and any race that the car might qualify to compete in. Often the local coordinator doesn't know the whole story.

Our rules prohibit them due to possibility for false trigger of finish line electronics.

Even if magnets allowed, the high-G stop that many tracks have may shake pieces loose. If so, local rules may prohibit putting them back on!

for most tracks in current use, rear weighting is advantageous... about 80% of weight on rear wheels; 20% on front wheel. For long tracks and constant slope tracks, less extreme distribution will usually perform better.

By the way, welcome to the group!

[Da Graphite Kid]

Cabrzama, let's not forget that even if the magnets are legal to use as weight - they are still magnets... How will they affect your pinewood derby pickup while it is rolling down the track? Our Pack's track has a steel tube structure along with metal screws and bolts (that rust!). I'm don't know that running a pwd car with magnets wouldn't slow it down regardless of where they are placed as weight. Just something to consider anyway.

Da Graphite Kid


PS: I've always toyed with the idea of using an electromagnet to push a pwd car down the track!

[Cabrzama]

All great advice. Thanks, guys. I checked with our coordinator last night and he gave me the green light for our pack's race. Obviously, some of the concerns you have raised are still valid. I will let you know how it goes. I may quickly build a back up car with my son in case this one flops.

[MaxV]

Regardless of the strength of the magnets, I strongly recommend using 5-minute epoxy, or hot-glue to attach the added weight at the weigh-in. This eliminates the possibility of the weights coming lose or shifting around.

[Darin McGrew]

Another option is a cyanoacrylate glue. They set quickly, are strong, and are easy to use. Look for one that can be used on wood and that can fill small gaps between the pieces to be joined.

[Cabrzama]

I glued the magnets down with crazy glue and let me tell you that stuff is FAST. I'll probably use that, unless someone has any bad experience using it.

We actually had somewhat of a freak accident using it, though. I had four small round magnets (a little smaller than a dime) in the formation of a square that I was going to glue into the bed of the truck. So, I applied the glue to the magnets, while holding them on the tips of my fingers. They were all attached (attracted) in that formation. But, as you know with magnets they tend to flip around because of the magnetic pull. Well, in just an instant after I applied the glue the two on the left flipped on top of the two on the right (while in my fingers). The force of them colliding threw small specs of glue right into my son's eyes (he was watching me closely). The two sets of magnets instantly set (they were ruined for what I was wanting to do). But more importantly, my son had the darn stuff in his eyes. It really irritated them so we flushed them out with water and that seemed to take care of it. We also had our neighbor (he's a doctor) take a look and he checked out fine. Pretty scary at first, though.

[Darin McGrew]

When I'm gluing parts on the car, I really don't like to start gluing a second part on until the first is either set or clamped. The exception might be for two parts that need to be positioned relative to each other, but even then I'd rather finish one before starting the next. So my preferred options are:

• to glue them on one at a time with cyanoacrylate glue, holding the parts together by hand while the glue sets;
• to glue them on one at a time with fast-setting epoxy, holding the parts together by hand while the glue sets and mixing another small batch of epoxy for each part; or
• to glue them on one at a time with a slow-setting epoxy, clamping each part into place before starting the next.

It just seems too easy to screw up when there are glued-up bits lying around, while you're working on some other glued-up bit.

[Stan Pope]

But more importantly, my son had the darn stuff in his eyes. It really irritated them so we flushed them out with water and that seemed to take care of it. We also had our neighbor (he's a doctor) take a look and he checked out fine. Pretty scary at first, though.

Scares me, and I'm fearless!

I like 5-minute epoly, too, because it matches the attention span of me and my Cub Scouts!

When adding weights to the rail design car, we lay the body on a piece of waxed paper, smear a lot of epoxy around inside the opening and push the weights into the (more or less) correct positions and smear more epoly in and then wrap the waxed paper over the top to squeeze everything into proper position. Sounds haphazzard, but it is very effective and excellent for 7 and 8 year-old boys!

[TDean]

Another gluing option -- in addition to Crazy-type glues and quick epoxy -- I have tried using the "rubbery" glues like Goop (probably silicon based -- I don't have access to it right now...). It sets up a bit slower than the epoxy (okay, a LOT slower) -- but the idea was that it would hold firmly, but be less rigid than regular glue -- hopefully forming a shock-absorbing cushion around the weight (like wrapping it in foam rubber). I know Grandpa and others suggest cushioning the weight could help -- especially on less than perfectly smooth tracks. It seems to work pretty well for me -- anyone think it's nuts?