Performance Report (1 November 2001)

The report is divided into the following sections:

Background:
When I finished building my TXT-1, I wired up a 8.4 volt 2000mah pack and took it running. While the truck had plenty of punch, I was a little disappointed with the 7 minutes of runtime (I know I’m greedy)… the truck slowed to a crawl just as I was starting to have fun. So I wanted to try a more extreme setup and see how it performed.

Back To Top

The Setup:
The truck was built with some mods from the start to improve performance.
The truck was fitted with a full set of bearings for faster speed, longer runtimes and more power - bearings are always considered a "must" on my trucks. I bought a set of Tamiya steering links for the Juggernaut and these were installed for steering purposes. These are much beefier than the stock rods. The steering muscle is provided by Futaba’s high performance S9402 servo.

The more extreme bit starts with the dual modified 14-turn double motors wired in parallel, and to supply the juice I built 2 7-cell 2000mah packs and wired them in parallel - that means I’ll be pumping 8.4 volts from 14 cells to the motors. The job of controlling the power was given to the Novak Super Rooster ESC with a cooling fan installed.

Detailed Specifications:

Back To Top

The Test:
Why was this setup a little extreme? Well, the Super Rooster is only rated to run up to 10 cells and 15-turn motors. On both cell count and motor configurations, I was stretching the limit a little… so I was wondering how things would hold up. More specifically, I wanted to see:

- how the truck would perform with the weight of 14-cells?
- what kind of runtime would I get with this setup?
- would my batteries overheat?
- how would the Super Rooster handle the load?
- would my motors melt?

Wanna know the results?

Back To Top

Performance/Handling
When I nailed the throttle I must say I was blown away! The acceleration was simply awesome and immediately I knew I was going to have a good time. The front left wheel lifted off more than 2" off the ground as the central gearbox unloaded power to the axles. The truck blasted off and I’m sure I heard the rims spin on the tires as this happened (I’m going to glue my tires tonight… trust me, you *need* to do this regardless of what your manual says).

I started with a couple of runs in an open grass field. Top-speed was very good. Although I don’t have a speed gun, this truck was definitely faster than my mod clod running Sapphires and 13-tooth pinions, it definitely accelerated a lot faster too.

Handling was really pretty impressive. I could make turns at full speed without the truck tipping over (of course, steering isn’t really tight). This surprised me because the weight of the 14 cells really added to a higher CG. I guess the anti-sway bars and the suspension setup did their job well.

I then headed to do some jumps off a small 2 foot hill. The general opinion is that the stock gearing (15 tooth pinions) is undergeared, so 13 tooth pinions would gear the truck for even more torque - man do I love the additional torque! This truck was powering up the hills very well and it was a very empowering feeling to have such control of the throttle even on steep slopes.

The truck launched off the top of the hills even more aggressively than with the 1 pack, stable through the jump and landed rear-wheels first in a semi-wheelie sort of fashion - highlight film material! I thought the additional cells would affect handling adversely, but to be honest, the difference was hardly noticeable. Note that I did add a spacer on the rear shocks to compensate for the additional weight though.

Love the power, love the handling, how did a runtime do?

Back To Top

Runtime
With 1 cell I got about 7 minutes before the batteries dumped on me. In preparation for this test I built two 8.4 volt packs and cycled them with my charger (3 cycles) before finally charging them up for battle..

I spent 5 minutes running at full-throttle on the open grass field and then another 7 minutes doing jumps and climbing tree-roots… The ESC got a little hot after that (more on this later), so after 12 solid minutes of fun, I took a 2 minute break, letting the fan continue to run to cool the ESC.

When things had cooled, I started timing again and the fun began again! The dual packs lasted me a combined total of 15.5 minutes before I noticed any loss of speed. Funny thing is that the dumping period seems to be longer too… at a slightly reduced speed, I was still able to enjoy a decent run for 2 out of the 3 minutes it took for the batts to dump completely.

I was told that I would get less than double the runtime with 2 battery packs wired in parallel but I actually got more than double. This could be due to the fact that I cycled the packs before this run so they performed better, but I wonder if it could also be because there was less heat build up and hence the cells actually delivered power more efficiently.

Back To Top

Battery/Motor Heat Build-Up
After 5 minutes of running in the open grass field, my batteries and motor were just slightly warm - a good sign. They were slightly warmer after the climbing and jumping session, but they the temperature was definitely still within acceptable limits. At the end of the whole run though, the batteries were pretty hot - just a shade cooler than when I finished my single pack test. So was my setup a failure when it came to trying to keep the battery temperature down? Nah… the cells actually took a much longer time to reach the same temperature… almost twice the time! I’d consider that a success.

I was also happy with the 13-tooth setup for my 14-turn motors. The motors never got too hot so that’s healthy… and runtime and speed were still awesome.

Back To Top

ESC Performance
The Super Rooster never gave me any problems. I’ve heard guys having problems with glitching when running low-turn motors, but there was no sign of this throughout the run. Brake was very strong throughout the run too.

I did however, have some problems with heat. After the 5 minute open field run, the ESC was warmer than the batts and motors but still okay. However, at the 12 minute mark I decided to take a break because the heatsinks were getting almost too hot to touch. I know the Super Rooster has thermal protection (i.e. it will shut down when things get too hot), but I wasn’t going to wait till then. I stopped the truck for a 2 minute rest, leaving the fan running to cool the ESC down (I stopped my stopwatch so during this time so these 2 minutes are not included in the runtime recorded above).

Perhaps I will try a full run without the break to see if the thermal protection ever kicks in, but to guys who are going to run low-turn modified motors, I’d recommend a cooling fan to keep things in check.

Back To Top

Conclusion
The hot ESC is a problem that I’ll have to look into, but I’d be lying if I said I wasn’t happy. I’m not sure if there’s a reason why running 2 packs instead of 1 would give me more punch, but I certainly felt it today. The truck was faster and more powerful than when running a single pack, and runtime was more than double. Nothing beats the feeling of running up slopes as if they were flat ground. The added weight of the second pack wasn’t really noticeable, and perhaps actually made the suspension work better with more sprung weight.

Future plans? I’m also toying with the idea of running dual 2400mah packs for even longer runtimes (but that’d mean an even hotter ESC…). One option I’ll certainly consider is Novak’s brushless motor setup when it is available next year.

For now however, all I can say is that I love this setup - try it if you have the means!

Back To Top

Pictures
Check out the pics of the setup:

Dual 7-cell 2000 mah packs	Y-connector with Deans Ultraplugs	14 cells installed with Speedmind strap	Pic of entire truck with electrronics	ESC and fan location	Shock spacers used due to heavier rear-end

Future plans? I’m also toying with the idea of running dual 2400mah packs for even longer runtimes (but that’d mean an even hotter ESC…). One option I’ll certainly consider is Novak’s brushless motor setup when it is available next year.

For now however, all I can say is that I love this setup - try it if you have the means!

Back To Top