LOSI LST XXL Conversion ideas

[mistercrash]

Originally Posted by brian015

I want to know how the heck that rock got in there too.

I still don't have the answer to that one.

I received my CC BEC today. Nice little thing, I replaced the blue heat shrink with a stronger one that has glue in it and has a shrinking of 3 to 1. So now both ends are sealed around the wires and will keep dirt, dust and water out of it. Now to decide where I will put it on the truck. I thought of just sticking it to the MMM with double sided tape. Since I don't use a switch, I cut off the part of the MMM mount that houses the switch so there is a space on the MMM casing behind the caps that looks big enough to stick the BEC to.

[mistercrash]

The CC BEC is installed and it's working great. I updated it to 6 volts and I noticed the difference on the steering servo. Quite a bit faster and torquey. I like it and it was easy to install. I chose to stick it to the MMM because when I need to remove the ESC, the BEC just comes with it. So does the cap bank the way I have everything set up.

[nuz69]

Hello,
this kind of temp seems to be normal as the hot weather, the weight of the truck and the no-finned can. Try to open your body, airflows can change everything !

[mistercrash]

The motor gets plenty of air flow so what it needs is a means to dissipate the heat using that air flow. So I'll take it easy on the motor until my Losi heat sink arrives. I'm hoping it will bring the motor's temp down enough for me not to worry about it anymore. This motor won't last very long if I run it at 200 degrees all summer. If this large heat sink can drop the temp to 180, I'll be happy. Any lower and I'll be very very happy.

[mistercrash]

There are some that may not agree with this but I did a few things to seal the openings of my NEU motor. I know the holes in this 1521 motor can offer some airflow to help cool it but where I run the truck, I don't get airflow, I get dust flow. There was way to much dust and debris getting inside the motor and bearings. So I sealed the rear with Goop around the wires and a piece of flat Lexan stuck to the motor with servo tape. For the front, I made a disk out of a thin piece of aluminum with just a hole for the shaft and two holes for the screws. Air can still get in and out of the motor but it is restricted. This should make it very difficult for dust and debris to get inside the motor. This is something I am trying here, I need to see if it will change the temp of the motor while running this way.

[Bondonutz]

Looks good Ray.
The aluminum duct work tape is the easiest way to block off them holes, Shoe-Goo around the wires does work very well but needs to dry a long while.

[JThiessen]

I use aluminum tape to do the same thing on mine. Not sure where it can be bought (I get it from work) - but that stuff works great in certain applications like this.

[mistercrash]

Aluminum tape!!! I have a roll of that somewhere! I should be slapped I never thought of using that, it's a great idea and would've looked better. I think I will remove the Lexan in the back and replace it with a piece of aluminum tape. Thanks for the idea.

[mistercrash]

I received the Losi motor heat sink today. It is very well made and has very large fins. It fits perfectly in my converted LST XXL and doesn't interfere with anything. What a difference this thing makes in motor temp. On the first test run on 4S, the motor ran at only 125 degrees. Tomorrow I will charge a couple sets of 3S and test running on 6S. Right now I am very pleased with this heat sink.

[mistercrash]

I received my pinions from Mike last week. Thanks Mike. So I tried going up one tooth on the pinion. 54 spur and 24 pinion with Crime Fighters MT tires on MT wheels. I had my new heat sink on the motor and went out on 6S. Outside temp was 91 F with the sun shinning, with the humidex, it felt more like 105 F. It was really hot in my garage and the temp of the motor before starting was already at close to 100 degrees. I ran hard for 20 minutes, non stop. Climbing, jumping, speed runs on asphalt, grass and gravel, donuts. Had a few tumbles, broke a front suspension arm again and the doohicky in a rear CVD that you put the grub screw in to hold the pin.

Temps were:

Motor: 170
ESC: 140
Lipos: 145
front and rear diffs: 140
Center diff: 170 at the tranny casing. So the CD inside might have been close to 200.

The heat sink really helps but I think I need to go back to the 23 T pinion to bring the lipo temp down. The front tires were balloning like crazy so I will take out the CD as I suspect that when it gets too hot, too much power is wasted on the front wheels making the motor rev needlessly. This truck is so tough. My old E-Revo would have been in pieces if I subjected it to what I do to this XXL.

[nuz69]

Hello, this kind of temp is the CD is normal, I hit the same in my truggy with a 1520/1Y. Are your wheels really balanced ? I had temp issue with non balanced wheels, which is always the case when you use monster truck wheels... Try maybe to do some air flow in the body, that helps a lot...
The hot batteries means that you are pumping of lot of amps, can you reming us your mph gearing setup, the weight of the truck and the type of batteries ? Maybe something is wrong in the transmission, and that would explain this temps.

[mistercrash]

This is what I had.

Differential Ratio: 3.3076923076923075
Transmission Ratio: 1.8333333333333333
Other Ratio: 1
Spur Tooth Count: 54
Pinion Tooth Count: 24
Total Voltage: 22.2
Motor KV: 1577
Tire Diameter (inches): 5.65
Tire Ballooning (inches): 0
Motor Current Draw: 0
Motor Coil Resistance: 0.008
Spur/Pinion Ratio: 2.25 : 1
Total Ratio: 13.64423 : 1
Tire Circumference (inches): 17.75 inches (450.85 mm)
Rollout: 1.30:1
Total Motor Speed: 35009.4 RPM
Vehicle Speed: 43.13 mph (69.28 km/h)
Effective KV Value: 1577
KT constant: 0.86 oz-in/A

Now I opened the tranny and took the CD out and put back the stock Traxxas spool. I checked the gears and all bearings and everything is in top shape in there. My wheels are well balanced. I always balance my wheels the best I can. There's no binding anywhere on the drive train, everything spins very freely. The body had holes in the front grill and a big round hole in the windshield. Plenty of air flow there. I was running a pair of Zippy-H 3S 5000 mah 20C. The truck weighs very close to 14 pounds with 3S lipos in it.

While I was working on the truck, I reinstalled the stock XXL Losi wheels and tires so I changed my gearing. Now when I use Brian's top speed estimator, I never factor in tire ballooning. Maybe I should so I recalculated with .25'' tire ballooning this time and this is what I'll be trying.

Differential Ratio: 3.3076923076923075
Transmission Ratio: 1.8333333333333333
Other Ratio: 1
Spur Tooth Count: 58
Pinion Tooth Count: 19
Total Voltage: 22.2
Motor KV: 1577
Tire Diameter (inches): 6.75
Tire Ballooning (inches): .25
Motor Current Draw: 0
Motor Coil Resistance: 0.008
Spur/Pinion Ratio: 3.05 : 1
Total Ratio: 18.51147 : 1
Tire Circumference (inches): 22.78 inches (578.52 mm)
Rollout: 1.23:1
Total Motor Speed: 35009.4 RPM
Vehicle Speed: 40.79 mph (65.52 km/h)
Effective KV Value: 1577
KT constant: 0.86 oz-in/A

[Manne]

Sounds Fairly good then except the lipos temp. Maybe 5000mah 20C don´t quite cut it?

"My old E-Revo would have been in pieces if I subjected it to what I do to this XXL."

So you are saying that the Lst is tougher then huh HUH!?

I really like this build now Mc, you are truley a real enthusiast ( or how it´s spelled )

[nuz69]

Ok
The batteries are too weak :(
Here in France we experienced very bad things with 100A discharge (5000, 20C) zippy lipo, even on light buggy, so in heavy Monster truck like yours ... Zippy batteries are often overestimated in their discharge capability, that's why you have this kind of temp in yours. The batteries will start to take volume in the time :( A good temp for batteries is 120 MAX !
Keep us posted if the setup without CD heat less !

[mistercrash]

Today is another extremely hot day in this heat wave we're having up here in the Great Toronto Area. So I took out the LST again in the same spot and let it rip on 6S. I over did it again as I blew the front diff after 5 minutes but I kept on going despite the loud clicking sound and at the 22 minute mark, I broke a front shock shaft. Good news is, the temps were great even though it is 40 degrees outside with the humidex.

Motor: 162
ESC: 134
Lipos: 109
Tranny case: 106
Front diff: 162
Rear diff: 141

So lesson learned here, when using the Top Speed Estimator, it is important to factor in the tire ballooning because since I didn't do it before, I was geared to low every time.