Pushing the limits of volting up and gearing down for a Crawler

[Lance Carbuncle]

Hey Guys,

Been lurking for a while and finally started jumping in and buying parts after doing a lot of studying.

I have an SCX10 II Kit version and a few weeks ago I bought a puller pro 3500kV and BLE PRo from Holmes.

I geared down to a 9T pinion and the performance is awesome and speed is just about where I want it to be on 4S LiFePo4 (13.2volts)

I was digging around on pinion sizes and see hot racing offers them all the way down to a 6T 32P size.

Soooo just for fun, I was thinking of going up to a 4500kV motor and down to a 7T pinion... to see what differences I feel. I am hoping for better low speed control and braking. Not that it isn't great already, but can it be better?

Not that I need more torque, but it seems the faster the motor spins, the better it responds, brakes, etc.....

I am not worried about breaking parts, I just enjoy learning stuff and researching new parts to upgrade as a break stuff ;)

Will these small pinions hold up with a good metal spur gear in these situations?

I plugged the numbers into the calculator I made and the top speed is identical between 9T and 3500kV and 7T 4500kV....

So what do you say?

Attached are the results from the changes in my calulator.

7T 4500kV



9t 3500kV

[whitrzac]

I ran 4s in my scx for a while, there's not much to be gained over 3s at this scale.

There was no noticeable difference in driving. The problem I had the most was that if something ever bound up, it was breaking. There was no safe zone between the 'is it stuck' and 'its broken'

[Lance Carbuncle]

Originally Posted by whitrzac

I ran 4s in my scx for a while, there's not much to be gained over 3s at this scale.

There was no noticeable difference in driving. The problem I had the most was that if something ever bound up, it was breaking. There was no safe zone between the 'is it stuck' and 'its broken'

I get that.... even at 3S, the comparisons still ask the same question in regards to gearing and kV.

I am running 3S and 4S, but LifePo4, so 9.9v for 3S vs 11.1 for Lipo, and 13.2v for 4S vs 14.8.... so my 4S is kinda in between 3S and 4S Lipo.

I actually run the 3S LiFe more often than not when crawling around and put in the 4S when I go on the trail or want to blast around on the flats.

[JohnRobHolmes]

3500 on 3s (or 4s life as it may be) is a pretty good all around system. You will get better braking and possibly better startup by running a 4500 with more geardown, but the lower resistance and inductance of the higher KV motor will make it more difficult to control in a bind. In other words, you will be more likely to break parts before you get any feedback that the rig is binding down. The higher KV motor will simply want to pull more power, and do it fast.

The other downside is the 7t pinion. It is very small and will be more likely to shear a tooth off the spur. The chordal length is so short, it will be noisy and wear fast too.

[Lance Carbuncle]

Thanks John,

One more scenario if you make it back to this post.....

Would you say that in this case, you would personally prefer the 3500kV setup above over a 2700kV setup with a larger pinion that gets the theoretical top speed nearly the same?

Here is a 12T 2700kV calculation.

[JohnRobHolmes]

I would choose the 3500 for snappier driving. The 2700 would be a little softer spooling but still drive with plenty of torque overhead, it is an extremely popular Kv. The gearing advantage would allow the 3500 to hold a little better from a static position. Spooling up a motor between 30,000 to 50,000 rpm is always going to be great performance in a single speed rig with the geardown available to the average crawler. Using more than 10 volts (volting up) optimizes most speed controllers volt rating, so the power doesn't have to come from too many amps. This is better for heat.

A two speed rig can deal with much lower KVs and still get a good low end control combined with wheelspeed. In a rig like the TRX-4 or trailfinder2, 1200 to 2200kv is a very sweet range that doesn't get uncontrollable in power delivery. It is much more controllable to drive a lower kv, especially with geardown of 35:1 or more. 60:1 range makes the lower Kv very controllable, but second gear around the 25:1 range gives the low Kv wheelspeed that wouldn't normally be available when geared properly for crawling.

[Jboucher]

Originally Posted by JohnRobHolmes

I would choose the 3500 for snappier driving. The 2700 would be a little softer spooling but still drive with plenty of torque overhead, it is an extremely popular Kv. The gearing advantage would allow the 3500 to hold a little better from a static position. Spooling up a motor between 30,000 to 50,000 rpm is always going to be great performance in a single speed rig with the geardown available to the average crawler. Using more than 10 volts (volting up) optimizes most speed controllers volt rating, so the power doesn't have to come from too many amps. This is better for heat.

A two speed rig can deal with much lower KVs and still get a good low end control combined with wheelspeed. In a rig like the TRX-4 or trailfinder2, 1200 to 2200kv is a very sweet range that doesn't get uncontrollable in power delivery. It is much more controllable to drive a lower kv, especially with geardown of 35:1 or more. 60:1 range makes the lower Kv very controllable, but second gear around the 25:1 range gives the low Kv wheelspeed that wouldn't normally be available when geared properly for crawling.

Does it apply to the bomber as well?

Sent from my Nexus 6 using Tapatalk

[Hydrocarbon92]

Torque spins your motor but power (watts) is what moves you straight up a rock (or not). This thing called "horsepower" calculates that, Torque*RPM/5252=HP. Gearing down multiplies the driveshaft torque.

If you want torque & speed there's another established way to get that. Use a physically bigger motor that will invariably have a lower KV and gear up instead. That puller pro basically embraces that with a 60mm can (vs 50mm), and you can get inrunners for boats that are the same diameter but much longer. Common motors are 70mm long 2850kv, 74mm 2250kv, and 90mm 1500kv.

[JohnRobHolmes]

Originally Posted by Jboucher

Does it apply to the bomber as well?

Sent from my Nexus 6 using Tapatalk

Applies to all vehicles.

[Lance Carbuncle]

Originally Posted by Jboucher

Does it apply to the bomber as well?

Sent from my Nexus 6 using Tapatalk

Here is an example using my new side by side calculator using the example of a Bomber with the differences being:

Car 1 12T Pinion, 3500kV 3S

Car 2 16T Pinion, 2700kV 3S

Top speed very similar but the 3500kV combo will have more torque from greater overall gear reduction.

[Jboucher]

Originally Posted by Lance Carbuncle

Here is an example using my new side by side calculator using the example of a Bomber with the differences being:

Car 1 12T Pinion, 3500kV 3S

Car 2 16T Pinion, 2700kV 3S

Top speed very similar but the 3500kV combo will have more torque from greater overall gear reduction.

Can you share that document?

Sent from my Nexus 6 using Tapatalk

[calcagno45]

He did here: Advanced Brushless Motor Vehicle Speed Calculator

[mewalsh100]

I went as small as a 8t 32P pinion on one of my rigs. You will eat them. Buy them by the half dozen. Ended up going back to a 10T pinion and 58T spur and it's definitely the sweet spot for me.

[Lance Carbuncle]

Originally Posted by Jboucher

Can you share that document?

You can get the link in my signature.

Enjoy and please give me feedback on how I can improve them and if you find any bugs.

Cheers

[Lance Carbuncle]

Here is a new version of the Comparison Configurator.

I have added a ton of calculations to help show the differences and their effects when comparing two setups.

[OldNASCARCrawler]

What/who is the source for 5mm shaft size 8T, 9T 10T Pinions?

Thanks