Senton Arrma 4S or 6S motor in a stock Senton 3S V2

[iep]

I'm casting about for ideas on ways in which I can reduce the cogging and increase the low speed torque of my Senton 3S. I'm not super excited about going sensored (cost an availibility of Castle being an issue in the UK)

Another forum member (K_BASH) suggested running a 6S (2050kv) motor with the stock BLX100 ESC on 3S and just gearing up a bit (26T vs 20T pinion). I think, makes sense from a current/power/heat perspective and I'd guess the top speed loss is minimal since the motor has more torque. I'm just concerned about the amount of faff that might be involved shoe horning that can into the V2 3S chassis.

An alternative might be the 2400kV motor and maybe just gear up a bit less?

Anyone else tried this type of thing?

Ta.

 

[dure16]

If your primary goals are to reduce cogging and increase low-end torque, why don’t you just gear way down on the stock electronics?

 

[iep]

'If your primary goals are to reduce cogging and increase low-end torque, why don’t you just gear way down on the stock electronics?'

Basically, I'd like to lose as little top end speed as possible.

Sure, this is definite cake/eat it stuff but just curious what options there are and what other people have tried.

 

[Kylerc]

I have a motor slightly larger than the blx 2050kv motor in my senton(converted to big rock)

it’s 2000kv and 18t pinion moves it pretty good on 3s but is a weapon on 4s. The low torque of the 3s system is quite frustrating and my system has a cheapo esc but still has loads of low end torque even though it’s quite overgeared.

don’t cheap out on the motors too much because I’ve gotten some that had weak magnets out of the box or were just outright poorly designed compared to HW or surpass motors.
Bad motors make cogging a lot worse.

 

[Engineer]

Or maybe switch to a sensored motor? There's a HobbyStar 4-Pole sensored SCT motor available in a bunch of kv's that runs around $65

 

[K-BASH]

I've tried 3660-3200kv
4068-2650kv
4074-2050kv
4076-2000kv
Must be careful with weight on the 3s lineup.above 3s the weight from bigger motor,esc,packs will ruin drivability quik..try an keep weight down..

 

[iep]

Well, that's flat out insane

I should re-qualify, I'm hoping to make my changes while keeping it on 3S. So, ideally, BLX100 ESC, 3S battery and just a new/alternative motor. As a result, only weight increase would be the motor itself.

Those Surpass 2650kv 3670 cans look prety promising but shipping from China (even via Amazon) is slowwwwwwww.

I could pick up a used arrma 2400kv locally for about the same. I might look out for one of those...

 

[K-BASH]

These motors will rip on 3s still.both on Amazon prime.2 day shipping

Never tried this 3674...would probly be a good one too

 

[iep]

Thanks but I'm in the UK. I see the same motors but all with ~1 month shipping.

I might try banggood instead and see what I can find there.

 

[iep]

Went for one of these at 2650KV:

https://uk.banggood.com/Surpass-Hob....html?cur_warehouse=CN&ID=516955&rmmds=search

I 'think' the stock pinion in the Senton is 20T so I'll probably order up a 23T 5mm pinion for this one and see how I get on.

 

[K-BASH]

Never personally ran that motor, but heard good things about it.it should have more torque an run cooler..those motors are rated for 18.5volts compared to 12volts stock.motor won't work as hardguys have run them on 6s.

 

[iep]

Thanks.

Neat wee app that. Just downloaded it.

Cheers.

 

[Kla912000]

Never personally ran that motor, but heard good things about it.it should have more torque an run cooler..those motors are rated for 18.5volts compared to 12volts stock.motor won't work as hardguys have run them on 6s.

View attachment 140732

You forgot to change the battery voltage on the gear calculator. You have it set at 10.9v. At least put it to 11.1v, or better yet, a fully charged 3s lipo is 12.6v.

 

[K-BASH]

The way I got app setup its hard to get 11.1 and 2650kv

 

[Kla912000]

I got the same app. All you have to do is tap the number "10.9" and you can change it.

 

[iep]

If you include the battery internal resistance, cables, ESC efficiency etc, the final voltage at the motor will be considerably less than the open circuit battery voltage.

TBH, 10.9V is probably pretty optimistic even for a fully charged battery once it's under load and you factor in the other losses.

On a good 3S battery the senton 3S will probably do ~47mph. The calculator would predict ~60mph for a stock car. The difference in speed between this ideal number and the actual is, largely, due to the battery voltage droop under load. if you set the app up with the stock values for the car (3200kv, 20T pinion) it'll spit out 47mph for a battery voltage of 9.8V.

This might seem pretty dramatic a loss in voltage but, if you assume that the car is drawing ~20A flat out, a fully charged batttery (12.6V), ESC efficiency of ~90% and that the battery plus wiring has a resistance of ~100mOhm, the actual battery voltage (as viewed at the motor) will be ~9.6V.

As a rule of thumb, using ~3.3V per cell as representative of the battery voltage under load is a good place to start.

There's a ton of appriximations in there for sure but it'll get you into the correct ballpark.

 

[K-BASH]

On my 8s speedruns I don't stay at 33volts it'll get down to 25 volts during pull.so I'm not worried about calculating a half a volt

 

[iep]

Nice data log!

So about 3.125V per cell under load. Seems about right. It'll vary loads from battery to battery, temperature..... So, as you say, chasing that last 0.5V is pretty fruitless.

Cheers.

 

[Kla912000]

If you include the battery internal resistance, cables, ESC efficiency etc, the final voltage at the motor will be considerably less than the open circuit battery voltage.

TBH, 10.9V is probably pretty optimistic even for a fully charged battery once it's under load and you factor in the other losses.

On a good 3S battery the senton 3S will probably do ~47mph. The calculator would predict ~60mph for a stock car. The difference in speed between this ideal number and the actual is, largely, due to the battery voltage droop under load. if you set the app up with the stock values for the car (3200kv, 20T pinion) it'll spit out 47mph for a battery voltage of 9.8V.

This might seem pretty dramatic a loss in voltage but, if you assume that the car is drawing ~20A flat out, a fully charged batttery (12.6V), ESC efficiency of ~90% and that the battery plus wiring has a resistance of ~100mOhm, the actual battery voltage (as viewed at the motor) will be ~9.6V.

As a rule of thumb, using ~3.3V per cell as representative of the battery voltage under load is a good place to start.

There's a ton of appriximations in there for sure but it'll get you into the correct ballpark.

Holy $hit! I'm not gonna even try to decipher all if that. Not trying to be that technical. It's really not that important to me. But thanks for the explanation!

 

[iep]

Ha! Yeah, quite a bit there

Good new is that you can cut to the end:

'As a rule of thumb, using ~3.3V per cell as representative of the battery voltage under load is a good place to start.'

Basically, when using the gearing app, just assume each cell in your battery is 3.3V.

1S = 3.3V
2S = 6.6V
3S = 9.9V

etc...