Car diet

So, I've put both my B4 and T4 on a diet! Both were overweight and I wanted to get both as close as possible to the ROAR minimum weights of 1499g for buggy and 1701g for truck.

The buggy was easy to get under weight, by installing Lunsford titanium screws and ball studs. I would have rather used aluminum screws, but AE doesn't sell an aluminum screw kit anymore :( They used to for the B3. Thus my final setup is:

Factory Team B4 Kit with all carbon parts
Factory Team aluminum in-line front axles
Factory Team titanium turnbuckles
Lunsford titanium hinge pins
Lunsford titanium shock mounts
Lunsford titanium screw kit
Lunsford titanium ball studs
Airtronics 94157 servo
AMB personal transponder
Futaba R604FS receiver
LRP Sphere Competition ESC with heatsink attached
LRP X11 17.5 motor with optional thin cooling plate
Reedy 35C 5000mah lipo battery
14g lead weight in back of chassis
AE wheels with JConcepts Bar Codes with standard inserts
JConcepts Illuzion body and wing
Race weight is 1500g, 1g above the minimum weight :)

The truck was a bit tougher to get close to the minimum weight. It has all the same equipment as the buggy except for the following:

LRP Sphere Competition TC with heatsink and fan
Orion 17.5 motor
Orion 30C 3800mah lipo battery
Race weight is 1724g, 23g above the minimum weight.

I was originally using my Reedy 35C battery, but the truck was 1785g, a whopping 84g overweight! (nearly 3oz!) Thus, I switched to the Orion battery. While lighter, the Orion battery felt as if it didn't have the punch that my Reedy pack did. I confirmed this at the last JBRL race at Hot Rod Hobbies. I ran the Orion battery in round 1 of qualifying, then the Reedy in round 2. The Reedy pack had noticeably more punch! And my lap times proved it as I was nearly 0.5 a second a lap faster! Unfortunately, my laps weren't as consistent, as I needed to get used to the increased punch.

My friend purchased an SMC 40C 4700mah pack in the Hot Rod Hobbies shop. I weighed this pack and it was only 24g (0.8oz) heavier than my Orion pack, but 37g (1.3oz) lighter than the Reedy pack! With its 40C rating, it should have close to the punch of the Reedy pack, but only weigh a little more than the Orion pack! I went into the shop and picked up 2 of these packs for myself! My truck's race weight with this pack is 1748g, 47g overweight. (1.7oz) To lose this extra 47g, I'd need to change to a lighter ESC or receiver or find more lighter parts, or maybe modify some parts myself! I have also found that the weight will change a lot, depending on what tires I'm running.

I tested the Reedy, Orion, and SMC packs on my Turbo35 charger at a 20A discharge rate and 6.6V cut-off. The results were:

Reedy 35C, IR=5.1, avg discharge voltage=7.54
Orion 30C, IR=9.0, avg discharge voltage=7.33
SMC 40C, IR=6.8, avg discharge voltage=7.48

The lower the IR (internal resistance) and higher avg discharge voltage, the more punch and power, the pack should have. Thus, the SMC pack has similar punch and power to the Reedy pack while being lighter! It also has more punch and power than the Orion pack, while only being a little heavier. I will be racing the SMC pack this weekend at round 4 of the OCRC Sat Series, comparing it to the on track performance of the Reedy and Orion packs.

Stay tuned for the results!