New to this forum, crawling, and looking forward to building my first SCX10 Rub

[gtione]

Hey guys

So in a weeks time I will be the proud owner of a new JK kit. I live in the UK and have a mate going to San Francisco on business this week so I begged him to bring me this home to save me some cash rather than buying locally.

Along with it I ordered a Tekin fx-r & 35t combo and a alloy servo arm.

This is where I need some help. I needed to make choices quickly to get it to his hotel in time so I did some frantic reading on here and made a few calls but I still have a few choices to make.

I am unsure of what battery option to go for. I had decided on a 2s set up. I am opting for a Hitec HS-7954 SH 7.4v servo which I was going to route straight to the b+ line and let the built in bec in the fx-r handle the RX.

As my mate can't fly with lipo's in the plane or so I think anyway I have opted to buy the battery and servo here. Before I do though I am still wondering if I should opt for a 3s set up and get a external CC bec. Do I need this and is the 35t motor bet suited to a 3 s set up? What are the real world benefits of 2s vs 3s set ups? I also don't see myself ever needing more than 2hrs run time in a single day to what capacity lipo should I be looking at or is it a case of the more the merrier. I suppose weight is a concern hey?

I am sure I will have a ton more questions but will leave that for another time. Thanks!

[BodiBuilt]

I will chime in with some general input...

A 2s battery puts out a little better than 7v to the motor when fully charged. A 3s battery puts out a little over 11v. More voltage to the motor = higher wheel speed

The larger the mAh rating, the longer the run time between charging, but at the expense of additional bulk/mass (overall dimensions) and weight. Many of us find a "happy-medium", but generally speaking you should have plenty of room to fit up to 5000mAh which will likely provide those 2hr run times.

If it were my build, I would set it up to run 3s including adding a BEC to reduce servo voltage... Just because you have the extra voltage available does not necessarily mean you have to use it (throttle finger control!), but on the occasion you wish you had the extra wheel speed, you will be glad it is available!

ETA: On a side note, running 11+ volts will wear out your motor brushes and comm a bit quicker than 7v (but it's worth it IMO!)

[k7zpj]

I am running smaller batteries in my SCX10 so that I have more options to relocate it for getting a lower center of gravity so the truck won't roll over as much. I have been running 2200 mah 35C 3S lipos. That gives me about 45 minutes of run time per battery. I have 2 packs so that one can be recharging while I running the other.

You will need an external BEC and receiver bypass so that you set the servo voltage to 7.4 volts. Running the servo at 11.4 volts wouldn't be good.
If you get the CC BEC you will need access to a castle link since the BEC comes set to 5.1 volts which is too low for the 7954.

[gtione]

Originally Posted by BodiBuilt

I will chime in with some general input...

A 2s battery puts out a little better than 7v to the motor when fully charged. A 3s battery puts out a little over 11v. More voltage to the motor = higher wheel speed

The larger the mAh rating, the longer the run time between charging, but at the expense of additional bulk/mass (overall dimensions) and weight. Many of us find a "happy-medium", but generally speaking you should have plenty of room to fit up to 5000mAh which will likely provide those 2hr run times.

If it were my build, I would set it up to run 3s including adding a BEC to reduce servo voltage... Just because you have the extra voltage available does not necessarily mean you have to use it (throttle finger control!), but on the occasion you wish you had the extra wheel speed, you will be glad it is available!

ETA: On a side note, running 11+ volts will wear out your motor brushes and comm a bit quicker than 7v (but it's worth it IMO!)

Yes the bec is a must if I go 3s I get that, I also now know that the CC bec has its servo output set to 5v and would need to be changed to output at 7.4v. Also excuse my ignorance but what is a "comm"?

Thx.

[gtione]

Originally Posted by k7zpj

I am running smaller batteries in my SCX10 so that I have more options to relocate it for getting a lower center of gravity so the truck won't roll over as much. I have been running 2200 mah 35C 3S lipos. That gives me about 45 minutes of run time per battery. I have 2 packs so that one can be recharging while I running the other.

You will need an external BEC and receiver bypass so that you set the servo voltage to 7.4 volts. Running the servo at 11.4 volts wouldn't be good.
If you get the CC BEC you will need access to a castle link since the BEC comes set to 5.1 volts which is too low for the 7954.

Thx for the input. OMG this is getting complicated, starting to fry my Brain never mind my servo..

What is a receiver bypass?

What does castle link cost to get?

Is 3s really worth all the extra expense or will I regret it if I don't get it now when I had the chance.. I realise I could upgrade at any time but it would make sense to do it now but don't wanna spend all the extra if the difference to me is not gonna be all that big.

Thx.

[gtione]

Originally Posted by k7zpj

You will need an external BEC and receiver bypass so that you set the servo voltage to 7.4 volts. Running the servo at 11.4 volts wouldn't be good.
If you get the CC BEC you will need access to a castle link since the BEC comes set to 5.1 volts which is too low for the 7954.

If I am running the servo direct to the b+ terminal running a 2s setup would this not be a better solution? I realise a 3s would over volt the servo.

[BodiBuilt]

Sorry for the confusion... Comm is short abreviation for commutator which is the part of the electric motor that the brushes ride against and is a part that will wear and need servicing at some point. Running higher voltage (3s) will shorten useable lifespan (faster than running 2s).

Castle link is basically a plug-in connection that allows the user to make changes to the settings of the Castle BEC... your local hobby shop may already have one (mine does) and provide this service for you for a fee.

And yes, it would be easier (and less expensive) to just run a 2s. If you ever feel the need to step up to 3s in the future, all you would need to do is wire in the external BEC, get it programed properly for your setup, and purchase a 3s battery.

[buddamonk]

Originally Posted by BodiBuilt

Sorry for the confusion... Comm is short abreviation for commutator which is the part of the electric motor that the brushes ride against and is a part that will wear and need servicing at some point. Running higher voltage (3s) will shorten useable lifespan (faster than running 2s).

Castle link is basically a plug-in connection that allows the user to make changes to the settings of the Castle BEC... your local hobby shop may already have one (mine does) and provide this service for you for a fee.

And yes, it would be easier (and less expensive) to just run a 2s. If you ever feel the need to step up to 3s in the future, all you would need to do is wire in the external BEC, get it programed properly for your setup, and purchase a 3s battery.

True! My personal choice is a 3S since i m also running a couple of lights too and they just shine mich brighter also. The BEC sounds more difficult than it is, so dont worry.