Inferno ST-RR Gearing Question

Dear all,
I am really really new to the brushless world.
I have a question regarding the gearing of my truggy. The diff is fitted with the 50T spur which comes in the set. I am to use the 2200kV MMM, and the truggy is mainly gonna be used for bashing around.
Which would the gearing ratio to go for bashing and a decent run time?(if I could combine all these with speed I would be going )
Thank you for your help. I am gonna post my project on the appropriate section of the forums.
Cheers

[simplechamp]

First we need to know how many cells you will be running. Then, the next thing to do is enter all the info into the gearing calculator, experiment with the numbers a bit (aiming for around 35-40mph is a good starting point) and go from there. If you have any questions as to what you need to enter into each field there are little question marks you can click on to help explain, otherwise ask here in this thread and we'll be happy to help.

Look forward to seeing your setup!

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

Thanks for your answer Simplechamp
I have used the calculator you have provided and I have come up with these:

Differential Ratio: 4.3
Transmission Ratio: 1
Other Ratio: 1
Spur Tooth Count: 50
Pinion Tooth Count: 10
Total Voltage: 22.2
Motor KV: 2200
Tire Diameter (inches): 5.8
Tire Ballooning (inches): 0
Motor Current Draw: 120
Motor Coil Resistance: 0.006
Spur/Pinion Ratio: 5 : 1
Total Ratio: 21.5 : 1
Tire Circumference (inches): 18.22 inches (462.82 mm)
Rollout: 0.85:1
Total Motor Speed: 47256 RPM
Vehicle Speed: 37.93 mph (60.92 km/h)
Effective KV Value: 2128.65
KT constant: 0.61 oz-in/A
Motor Torque: 0.38 ft-lbs
Final Torque: 8.26 ft-lbs
Final Power: 2664 watts (3.6 HP)

I am opting to use a 6S 30C and 5000mAh Lipo

I have noted that as I increase the pinion gear's T number and lower the Spur Gear's T I am getting higher theoritical end speeds. If I am correct to this then the torgue is lowering accordingly?
I am interesting in bashing and be a bit speedy on the field.
Is there a way to estimate the run time on a 6S battery with the aforementioned characteristics?
I am going to post in the project session soon enough for everyone to have a look and present their opinion.

[simplechamp]

Yes, your observation about torque is correct. What you can look at for torque is the rollout number also. This ratio is the number of inches the wheels turn for each revolution of the motor. So with your gearing the tires are turning 0.85 in. for each revolution of the motor. This is actually a very high torque setup. If you had a rollout of 3:1 this would be a high speed but very low torque setup because each revolution of the motor is turning the wheels 3 inches. I try to keep my setups between 1:1 and 1.5:1 and they have worked out well that way, with a good balance of low-end torque and good top speed.

If you haven't already purchased your lipos you might consider going with 5S, because on 6S your RPM are pushing towards 50k which is pretty high, I would suggest trying to keep them in the 30-40k range. Even on 5S you will still be able to gear for 35-40mph and still have plenty of torque.

thank you for your answer. I have seen some fellows to use a 15T pinion gear, which lowers the torque to about 5ft-lbs but the overal speed increases considerably. Would that be something to consider for general bashing around?
I haven't bought the battery as of yet, so I am open to suggestions.

[simplechamp]

If you already have the 2200kv motor and still need to buy lipos I'd go with 5S. You can use a larger pinion then (and depending on the motor mount used you might not be able to use 10T pinion, I know the smallest I can use on my truggy is 13T, and that is with a 52T spur) and can still gear for 40mph and have a well rounded system with balanced low-end torque and top speed. 5S will also bring the RPM down to about 40k which is more reasonable and will be less hard on the motor, and your rollout ratio will still be well within the acceptable range. Overall, the 2200kv on 5S would make for a great bashing setup.

Hello everyone.
As I am to finally get this done (after some stuff happening along the way),
I have some questions still on my mind.
Looking at the speed calculator and I noticed the following;
a 52/12 Spur to Pinion ration yields a theoritical Vmax of 37.69mph with a motor speed of 40700 RPM on a 5S battery.
A 52/13 spur to pinion on the other hand increases the Vmax a bit to 40mph and lowers the Rollout to 1.06:1 which is closer to the 1:1 ratio.
Which is the "best" one to use theoretically speaking?
Is there a way to calculate the running time on these settings?
I will try to avoid using the 50T spur gear as this is a metal one and I read that is better to opt away from metal spur gears in case the mesh fails.

[pinkpanda3310]

Originally Posted by Achaios

Which is the "best" one to use theoretically speaking?

The best one would be determined by what temps you get from the esc and motor. There is also a lot of variables like battteries, climate, driving style, where you run (boggy sand through to hard top) which affect temps. Most (if not all) people have a range of pinions in their kit. If you don't already have one get yourself an IR temp gun and check the temps regularly, cheap way to look after your gear.

[simplechamp]

I would start out with the 52/13 and go from there. Run it and watch temps closely, and you can decide how you like the torque and top speed, and also decide if the temps are reasonable. I can say with a 1.06:1 rollout ratio you will have plenty of torque.

As for the spur gears, I personally have never had an issue with steel and choose to use those, but some people do prefer plastic, it's a personal preference you can experiment with.

[nuz69]

Depending of your driving style, a higher top end (bigger pinion) will provide an higher torque impression, it's like the brushless motor can compensate indefinitly the higher load. But what we don't always realise is that this draws more amp from ESC and batteries.
I would go with longer motor than the 1515 for a truggy.

[simplechamp]

I say the 1515 is fine. When I had one in my truggy it never broke a sweat and had all the power I could ask for. The only reason I went to a 1518 was because of the Castle clearance sale.

[nuz69]

Yes a 1515 can do the job, but a 1518 or 1520 can do it with better efficiency for the same power (geared for the same top end), meaning longer runtime.

Hello. Thank you all for your replies.
So, using a lower kV motor with the appropriate gears ratio for same top end speed, yields a longer runtime? Does this include changing batteries as well? i.e. from 4S to 5S?

[nuz69]

No, you can keep the same voltage and have better runtimes, but you can up the voltage with a low Kv motor like the longer Castle motor to get even more runtime, for example the 1520 1600Kv and 6S battery.

OK :) I think I start to get the grip of this theory part. Same voltage, with a lower kV motor will yield longer runtimes compared to a setup geared for the same speed but with a higher kV motor. :)