Mugen MBX5T runtime help
 

Ok, got my Mugen from ebay, and I really like it. Took my hobbywing 80A and 2000kV motor and dropped it right in since it came converted already. Bought a set of AKA city blocks (premounted) and hit the track. My setup is duel 7.4 lipo's 5000 at 35c. My gearing is this:

front/rear dif ratio: 4.3
transmission ratio: 1
spur gear: 46t
pinion gear: 18t
battery voltage: 14.8
motor: 2000kV
tire diameter: 5.5"
ballooning: 0.5"

This gives me the the following results:

Spur reduction ratio: 2.56:1
total reduction ratio: 10.98889:1
Tire Circumference: 20.42 inches (518.68 mm)
Rollout (?): 1.86:1
Total Motor Speed (?): 29600 RPM
Theoretical Maximum Vehicle Speed (?): 52.09 mph (83.67 km/h)
Calculated Loaded KV Value (?): 2000
Calculated KT Constant (?): 0.68 oz-in/A

My problem is I think that I'm overgeared. I was going to drop to a 15 or 16 tooth gear. I need to make 15 minute main and I only lasted 9.5 minutes!

I could run 2 4s 5000's in series to get the time but I don't want to run that much battery if I can avoid it.

What is the ideal numbers I'm trying to get with gearing? What total reduction ratio should I be trying to get, final spur reduction ratio?

Is it possible to go 15-20 on a set of good 5000 30-40c batteries running at 14.8 (7.4x2)? I want to avoid running at 5C because the 80A hobbywing is rated for 4C.

Thanks,

X

52mph is wayy too high. gear for just under 40.

How hot does that setup get? gotta be smokin'

Yes too hot! Although I just got my Turnigy heat sink and fan and it is almost too big but I am overgeared. I'm gearing down and going to put a hole in the front for airflow. Besides mph what should I be trying to get with the gearing numbers?

Can other people make 15-20 min mains with a 14.8 5000mah pack?

I think you should be able to make a 15min main with a 2000kV motor on 4s. Most people look at the top speed to set their gearing. As brushlessboy said, go for just about 40mph...that's a good general target for most tracks. If you have a huge track, you might want to gear for a bit more top speed for long straights, and vice versa for small tracks. If you gear for say 37mph, you'll probably make the main fine.

Here's some info that may or may not be of help to you... i think you should be able to make 15 minutes easily enough =)

Packs: 2x 2S2P 28C SMC 9000mah Lipos wired in series for 4S
Vehicle: MBX5-T (Geared 14/46 Long Shank Pinion - apparently 4.8kg RTR says my unreliable scales at home)
Electrics: MMM/Tekno Neu 1512 2.5d/f
Race/s Vehicle Run In (Runtime): 2x 6 minute qualifiers
Temps: Batts: 110f - Motor: 130f - ESC: 110f
Cell Voltages BEFORE Charge: Pack 1 - 3.72v/3.74v - Pack 2 - 3.72v/3.74v
Cell Voltages AFTER Charge: Pack 1 - 4.20v/4.20v - Pack 2 - 4.20v/4.20v
Mah Charged Into Pack: Pack 1 - 6462Mah - Pack 2 - 6572Mah
Charge Time: 111 Minutes : 53 Seconds
Peak Pack Voltage: Pack 1 - 8.422v - Pack 2 - 8.407v
Pack Resistance: Pack 1 - 3mΩ - Pack 2 - 5mΩ

Thanks guys,

I got a 15t pinion in today and went down to the track. Still has good top speed, runtime was about 18 minutes. I think 14 will give me exactly what I need. I guess I should invest in 6-8K packs to guarantee my run time.

X

Just get multiple 5k packs and switch them out rather than 1 heavy battery.

I have multiple 5000mah packs, and I switch them out between races. Qualifiers are 5 minutes. My issue is only the main. I think I'm 1 gear away from making 15 minute run times. My local track runs nitro with electric so we have 15 min mains. After practice today, I feel better running the 15t with a pair of 2s1p 5000 7.4v packs. With a 14t I should make 15 min mains no problem. In the off season I'll get a pair of 6 or 8K packs just to be sure in case they raise the mains to 20 minutes. Nothing is worse than trying to beat nitro only to not have enough batteries.

X