Need Some Input before i burn something up AGAIN !!!! - RC-Monster Forums

TroubleMan · **Need Some Input before i burn something up AGAIN !!!! -** 04.20.2011, 03:08 AM

Hi all,
Kinda new around here and wanted to post my build but working and getting time was like pulling teeth !!! Anyhow i fried my RX8 a few days ago and i really was surprised. i did run the truck for 10~15 minutes 2 or 3 times before this took place at the time it poofted i was running
19 pinion
48 spur
6 cell 40c
1717
RX8
any input would be helpful, when i started this build i wanted to use Monster XL but i never planned to run anything higher than a 6 cell so i figured the rx8 would holdup. Now i'm thinking i want a XL but maybe my gearing killed it with the wheels

JERRY2KONE · **Welcome -** 04.20.2011, 05:31 AM

Well welcome to RCM troubleman. Hope you can enjoy your stay with us. Not so sure about your setup, because that 1717 can draw a lot of amps at its peak. The RX8 is a very nice ESC, but from most of the info and posts I have seen it is not great for handling high amp setups. I am seeing some MMM's doing OK with that motor, but I always go on the side of caution and believe in overkill when it comes to having some wiggle room with electrical setups. I would go with the CC XL if I were you. Money wise that is probably your best bet. If your budget is bigger than look into the MGM Comp Pro lineup. Read around here, because there are more and more CC 1717 setups showing up in various configurations, and most seem to work pretty well. I have three of these motors, but my stuff is in transit because we just moved. Personally I think that motor is just a bit too much for the RX8. Just my 2cents.

Arct1k · 04.20.2011, 06:35 AM

I would double check your gearing. That seems v high with a cd conversion.

brian015 · 04.20.2011, 07:07 AM

I guessed at your tire diameter, but it looks like you're a bit overgeared:

Differential Ratio: 3.3076923076923075
Transmission Ratio: 1
Other Ratio: 1
Spur Tooth Count: 48
Pinion Tooth Count: 19
Total Voltage: 22.20
Motor KV: 1580
Tire Diameter (inches): 6.5
Tire Ballooning (inches): 0
Motor Current Draw: 0
Motor Coil Resistance: 0
Spur/Pinion Ratio: 2.53 : 1
Total Ratio: 8.35628 : 1
Tire Circumference (inches): 20.42 inches (518.68 mm)
Rollout: 2.44:1
Total Motor Speed: 35076 RPM
Vehicle Speed: 81.17 mph (130.39 km/h)
Effective KV Value: 1580
KT constant: 0.86 oz-in/A
Motor Torque: Amperage not specified...
Final Torque: Amperage not specified...
Final Power: Amperage not specified...

bruce750i · 07:59 AM

If their 1/10 pro esc can't handle a 1/8scale motor, why would their 1/8 esc handle a 1/5 motor? Geared for 81mph is pushing your luck either way.

brian015 · 04.20.2011, 09:19 AM

Quote:

Originally Posted by bruce750i

If their 1/10 pro esc can't handle a 1/8scale motor, why would their 1/8 esc handle a 1/5 motor? Geared for 81mph is pushing your luck either way.

1717 is not a 1/5th scale motor - CC sold it for use with the MMM.

DrKnow65 · 04.20.2011, 09:27 AM

My Losi 8T has had it's 1717 on 6S lipo pulling the kids on the skateboard with a MMM without issue, so I can verify the two work well together :-)

That being said I would buy the XL (version 2) if I had to replace the MMM. I love the integrated data logging. It's a must have in my RC's now. If you look at a MMM and an eagle tree logger the price of the XL looks way more reasonable.

P.s. My XL runs COLD in my 8ight buggy with a 1518 (reasonably similar KV to the 1717) on 8S geared to the moon :-)

ikpthegame · 11:06 AM

Quote:

Originally Posted by brian015

I guessed at your tire diameter, but it looks like you're a bit overgeared:

Differential Ratio: 3.3076923076923075
Transmission Ratio: 1
Other Ratio: 1
Spur Tooth Count: 48
Pinion Tooth Count: 19
Total Voltage: 22.20
Motor KV: 1580
Tire Diameter (inches): 6.5
Tire Ballooning (inches): 0
Motor Current Draw: 0
Motor Coil Resistance: 0
Spur/Pinion Ratio: 2.53 : 1
Total Ratio: 8.35628 : 1
Tire Circumference (inches): 20.42 inches (518.68 mm)
Rollout: 2.44:1
Total Motor Speed: 35076 RPM
Vehicle Speed: 81.17 mph (130.39 km/h)
Effective KV Value: 1580
KT constant: 0.86 oz-in/A
Motor Torque: Amperage not specified...
Final Torque: Amperage not specified...
Final Power: Amperage not specified...

your a little off, heres what i got, i used the 5b tires since thats what hes got from the looks of it

Differential Ratio: 3.3076923076923075
Transmission Ratio: 1
Other Ratio: 1
Spur Tooth Count: 48
Pinion Tooth Count: 19
Total Voltage: 22.20
Motor KV: 1580
Tire Diameter (inches): 5.311
Tire Ballooning (inches): 0
Motor Current Draw: 0
Motor Coil Resistance: 0
Spur/Pinion Ratio: 2.53 : 1
Total Ratio: 8.35628 : 1
Tire Circumference (inches): 16.68 inches (423.8 mm)
Rollout: 2.00:1
Total Motor Speed: 35076 RPM
Vehicle Speed: 66.32 mph (106.54 km/h)
Effective KV Value: 1580
KT constant: 0.86 oz-in/A
Motor Torque: Amperage not specified...
Final Torque: Amperage not specified...
Final Power: Amperage not specified...

TroubleMan · 04.20.2011, 11:20 AM

Thanks everyone ! i figured i had it geared a little high but i geuss i felt better cause i had a 25 pinion on it while i was building it and i took the truck along to get wheels and the guy at the hobbyshop saids your geared for 100 mph ! joking but i remembered i didn't buy a gear for the truck so i went with the 19 and i know i should have been looking at a 14~15 count. i always look at the ratings on the stuff i buy and the RX8 on paper kills the MMM it's why i used it on my MRX3 but 210 amps vs. 150 amps any thought's ? also would this had happend if i'd had the CC XL it's hard keeping up with trucks running 2200 and 2650 not that it's a race but would like to stay in the pack when we run !

brian015 · 04.20.2011, 11:43 AM

Quote:

Originally Posted by ikpthegame

your a little off, heres what i got, i used the 5b tires since thats what hes got from the looks of it

Differential Ratio: 3.3076923076923075
Transmission Ratio: 1
Other Ratio: 1
Spur Tooth Count: 48
Pinion Tooth Count: 19
Total Voltage: 22.20
Motor KV: 1580
Tire Diameter (inches): 5.311
Tire Ballooning (inches): 0
Motor Current Draw: 0
Motor Coil Resistance: 0
Spur/Pinion Ratio: 2.53 : 1
Total Ratio: 8.35628 : 1
Tire Circumference (inches): 16.68 inches (423.8 mm)
Rollout: 2.00:1
Total Motor Speed: 35076 RPM
Vehicle Speed: 66.32 mph (106.54 km/h)
Effective KV Value: 1580
KT constant: 0.86 oz-in/A
Motor Torque: Amperage not specified...
Final Torque: Amperage not specified...
Final Power: Amperage not specified...

Yes - they are 5b tires - but they are larger than 5.3 inches (the tires you used in the calculator are Savage tires - not 5b). My 5b bowties are 6.8 inches. So I guessed a little less than that for his tires.

TroubleMan · 04.20.2011, 12:52 PM

yes sir they are B5's 62 isn't but 10 mph's or so more than i wanted as a top speed. i really would like to keep the speed i have BUT ! i would like for this to be a middle of the road deal nothing on the edge so saying that if i get a CC XL and drop to a 18 cause i'd like just a little less topend would the controller survive ? i'd also like to try 8s with 14 pinion and see if the truck felt more driveable. im far from a newb but this 1717 is just a heli motor gone wild ! i wanted to go as far as Brian015 build but i didnt have the chops !

brian015 · 04.20.2011, 01:00 PM

Quote:

Originally Posted by TroubleMan

yes sir they are B5's 62 isn't but 10 mph's or so more than i wanted as a top speed.

But you are closer to 80mph top speed if my 6.5" diameter is close. Can you measure your tires so the calculation is accurate?

TroubleMan · 04.20.2011, 01:06 PM

WOW not reading my own tread ! i need to lower the pinion alot more

TroubleMan · 04.20.2011, 01:18 PM

6.2 would be fair 160mm is what this digital dohicky saids !

brian015 · 01:30 PM

You can try running your own numbers here:

http://www.scriptasylum.com/rc_speed/top_speed.html

but this is what I get:

Differential Ratio: 3.3076923076923075
Transmission Ratio: 1
Other Ratio: 1
Spur Tooth Count: 48
Pinion Tooth Count: 19
Total Voltage: 22.20
Motor KV: 1580
Tire Diameter (inches): 6.2
Tire Ballooning (inches): 0
Motor Current Draw: 0
Motor Coil Resistance: 0
Spur/Pinion Ratio: 2.53 : 1
Total Ratio: 8.35628 : 1
Tire Circumference (inches): 19.48 inches (494.74 mm)
Rollout: 2.33:1
Total Motor Speed: 35076 RPM
Vehicle Speed: 77.42 mph (124.37 km/h)
Effective KV Value: 1580
KT constant: 0.86 oz-in/A
Motor Torque: Amperage not specified...
Final Torque: Amperage not specified...
Final Power: Amperage not specified...

Edit: If you then click on the gear symbol next to estimated top speed, you'll get a table of pinions vs. speeds that will help you choose an appropriate pinion:

10T 40.75 mph
11T 44.82 mph
12T 48.90 mph
13T 52.97 mph
14T 57.05 mph
15T 61.12 mph
16T 65.20 mph
17T 69.27 mph
18T 73.35 mph
19T 77.42 mph
20T 81.50 mph