Can someone explain the runtime disparity between these two rigs?

[BashNSlash]

Observation: My SCX10 ii (from the raw builder's kit) has significantly longer run time vs my TRX-4.

Details:
SCX10 ii - Team Raffee 27t rebuildable brushed motor + Hobbywing 1080 ESC + Traxxas receiver + 20kg servo. Stock everything else.

TRX-4 Defender - Castle slate 2850kv sensored brushless motor + Castle Mamba X ESC + Flysky receiver + 20kg servo. Stock everything else.

Tests: Using a 5000mah 2s Lipo (50c, Gens Ace), I'm getting in excess of 3h of runtime on the SCX10. Using the same battery and following the same trail (going over the same objects), I'm getting at most 1.5h with the TRX-4.

NOTE: My son's TRX-4 Tactical and my wife's TRX-4 sport get similar battery life (slightly better on the Sport, slightly worse on the Tactical).

I would assume the brushless system would last longer (the TRX-4 using the stock traxxas motor/esc lasted only an hour), but is the extra weight of the TRX-4 impacting it that much? The TRX-4 weighs approx. 8 lbs and the SCX10 is around 5lbs.

I'd love to get better run time with my TRX-4 as swapping batteries out in the cold winter isn't very pleasant.

Any insights would be appreciated.

[svt923]

Weight will play a part, the TRX-4 is probably at least a pound heavier than a SCXII unless you added a bunch of weight.

How much are you driving the TRX-4 around in high gear? The 26:1 stock gear ratio of the TRX-4 in high is going to be much less efficient than the 40+:1 gear ratio of the SCXII. Also check the pinion spur mesh on the Traxxas, many of them end up overly tight using the recommended settings which will cause excess drag.

[BashNSlash]

Originally Posted by svt923

Weight will play a part, the TRX-4 is probably at least a pound heavier than a SCXII unless you added a bunch of weight.

How much are you driving the TRX-4 around in high gear? The 26:1 stock gear ratio of the TRX-4 in high is going to be much less efficient than the 40+:1 gear ratio of the SCXII. Also check the pinion spur mesh on the Traxxas, many of them end up overly tight using the recommended settings which will cause excess drag.

The TRX-4 is approx. 8lbs and the SCX10 is around 5lbs.

I've experimented with driving only in low gear, only in high gear, and a mix of the two. High gear only gives me the longest life (1.5h) and low gear is the worst. Even the Castle data log confirms that low gear uses more voltage out of the pack.

My TRX-4 is perfectly meshed - it's one of the quietest rigs you'll hear! I've also makes sure there's no binding or anything like that. Seeing how the other two TRX-4 perform similarly, I would assume there are no problems preventing it from being more efficient.

If weight is the deciding factor, I'll keep the SCX10 pretty much all plastic.

I feel so tempted to install the 1080 ESC and another brushed motor to see how it compares to the Mamba X combo. I would be shocked if that's the reason why my SCX10 is so efficient.

[OutLore]

Originally Posted by BashNSlash

The TRX-4 is approx. 8lbs and the SCX10 is around 5lbs.

That's a 60% increase in weight. I would say that right there is where the bulk of the difference in run time is.

[BashNSlash]

Originally Posted by OutLore

That's a 60% increase in weight. I would say that right there is where the bulk of the difference in run time is.

That gives me a good place to start. The defender body is like 800g and I have a proline body that's closer to 250g that I'll have to try and replicate the same trail to see if there's a noticeable difference in runtime.

[WHITE-TRASH]

Portals and a 2 speed pretty much double the gear train the power is transmitted through. Parasitic drag and weight make a huge difference.

[Sneetches]

I was also under the impression that a 2200kv motor is closer to a 27T than the 2850kv. If that's the case then you essentially have a double whammy like WT mentioned, a heavier rig with more drivetrain drag and a faster motor vs a lighter, more simple drivetrain with the slower motor.

[BashNSlash]

Thanks for all the insight, guys! I really appreciate it.

It sounds like I either have to access these run times or look at getting a 10,000mah battery to make up the difference

[MasteroFlego]

Originally Posted by BashNSlash

Thanks for all the insight, guys! I really appreciate it.



It sounds like I either have to access these run times or look at getting a 10,000mah battery to make up the difference

Get a 3s battery, then you can gear down more on your trx4 for the same speed at higher efficiency

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[Jim85IROC]

Originally Posted by MasteroFlego

Get a 3s battery, then you can gear down more on your trx4 for the same speed at higher efficiency

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Great advice!

When I put portal axles into my Gen7, there was such a huge gear reduction that I had to run 3S just to keep the truck going above walking speed. The result is that last week I ran it for 2 hours on a 3300mah 3S pack.

[BashNSlash]

Originally Posted by MasteroFlego

Get a 3s battery, then you can gear down more on your trx4 for the same speed at higher efficiency

I have a 3s, but as a matter of convenience I'll stick with the 2s lipos (I have four of them) and 8.4v nimh (I have at least six of those). Because I have multiple trucks that share batteries, I don't want to change gearing just for the one pack.

Also, 3s tends to break stuff on my trucks, at least it has several times with my Slash 4x4

[MasteroFlego]

Originally Posted by BashNSlash

I have a 3s, but as a matter of convenience I'll stick with the 2s lipos (I have four of them) and 8.4v nimh (I have at least six of those). Because I have multiple trucks that share batteries, I don't want to change gearing just for the one pack.



Also, 3s tends to break stuff on my trucks, at least it has several times with my Slash 4x4

Going to 3s is still the best way to get better runtime though, as you'll probably never be able to shed enough weight to match your scx10.

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[BashNSlash]

Originally Posted by MasteroFlego

Going to 3s is still the best way to get better runtime though, as you'll probably never be able to shed enough weight to match your scx10.

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I may give this a try and see how things go

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[svt923]

Originally Posted by BashNSlash

I've experimented with driving only in low gear, only in high gear, and a mix of the two. High gear only gives me the longest life (1.5h) and low gear is the worst. Even the Castle data log confirms that low gear uses more voltage out of the pack.

It is not low gear that causes more amp draw, it is more than likely you grabbing more throttle to compensate for the lost wheel speed from the additional gear reduction.

[BashNSlash]

Originally Posted by svt923

It is not low gear that causes more amp draw, it is more than likely you grabbing more throttle to compensate for the lost wheel speed from the additional gear reduction.

This might be true. My walking pace didn't change, so I had to keep the truck going at my speed, which means more throttle.

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[jokersinsanity]

I know with the 2 different scx10s and the custom 6th scale, the mamba x puts batts on conserve mode or something. My scx10 8lbs was getting over 4 hrs on 1 3s 5000mah batt. Where as the 6th scale was getting close to 3 hrs on the samd setup and she was over 15lbs

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[durok]

Chiming in on the "switch to 3S" recommendation...

Especially as low as the TRX-4 is geared, it really is a great idea.

Increases runtime quite noticeably.

I did it on a HH 550 21t-powered Ascender (which isn't geared down nearly as much) and I haven't broken any parts - and it has been thrashed pretty hard.

As JohnRobHolmes always says, Volt Up, Gear Down!

[Cincygoon65]

I have a trx4 with a mamba x, and 1900kv motor. The truck weighs in at 7.91lbs with the battery. I run a 1400 mah 3s small gens ace pack, i get about an hr to hr and a half with mixed hi/low gear driving.

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[BashNSlash]

Originally Posted by Cincygoon65

I run a 1400 mah 3s small gens ace pack, i get about an hr to hr and a half with mixed hi/low gear driving.

How in the hell? Alright, I'm going to try the 3s this weekend and see how things go Any recommendations for the pinion if I've got the 2850kv slate and want to keep it around stock speed or slightly slower? I'm all stock with gearing right now.

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[durok]

I'd go down 2 teeth on the pinion.