BKoz559

My Feedback: (3)

First, start off with the stock gearing to form a basis for comparison. You wouldn't know what needs to be changed until you know how the stock setup performs. The motor you chose is fast but, it's fine for 2S.

Now, you're theories on motor RPMs and gearing are a little foggy but you seem to have an idea of the concept. Small pinion against a large spur increases torque but lowers top speed and generally speaking it eases the load on the motor. Conversely, a large pinion against a small spur decreases torque and increases top speed (up to the motors power limits) but it puts increased load on the motor. Think of the difference between 1st gear and 10th gear on a 10 speed bicycle. You need to consider these factors when changing gear ratios.

If you used a low KV motor then you would have to increase the pinion size or decrease the spur size or both in order to regain speed. Low KVmotors run cooler than high KVones so this practice is acceptable; assuming all other variable are constant. Again, run your truck with the new motor and watch the temperature. If it only gets warm after about 10 minutes then you can safely increase towards a taller gear ratio. You should invest in a IR temp gun, they're about $25 at a hardware store. Don't let the motor exceed 150-160 for long. A conservative temperature goal is around 115-120 with about 100 or so being a "cool" safe temp. I've seen guys at the races get up to 130-140 which is still a reasonable temp. It's just more than what I'm comfortable with.

BKoz559

My Feedback: (3)

Another thing I want to note is that the battery you chose will work with your setup since the motor probably will never draw 120A of current. It probably won't ever draw more than 50-60-70 amps at its peak. However, if you attach a "hotter" / more powerful motor to the same ESC and use the same battery then you can potentially experience a battery failure. Your battery can supply 99A which, as I stated, will be adequate for your motor. But, the ESCis capable of pulling up to 120A; a good 20% more than the battery's rated capacity. This can be dangerous if you change motors in the future. For the next battery, choose one that is rated to supply atleast 120A. An example would be a 2S 4000mAh 30C.

jwalk33

Thanks BKoz559,

BKoz559

My Feedback: (3)

I dont see any issues with your current setup in that regard, except that you will have relatively short run times. The advantage of a lower mAh pack is that it is physically smaller and therefore lighter than a higher mAh pack. It wont make a big difference in this truck's performance because we're talking about a matter of grams. But in a lightweight touring car, a few grams can noticably alter the handling characteristics.

I like to use packs in the 5000-6000 range for longer run times but at the track, I use a few different packs in the low 4000s and even a 3500 pack so I can keep the weight down.

jwalk33

Ok, I just bought a Tunigy TrackStar 4168 2650kv motor and Turnigy nano-tech 4000mAh 3S 45-90c lipo battery.

Maybe too much power for the Ripper but at leaset I'll have it when/if I buy something that can handle it.

Well, just realized that this is a 550 size motor so it will not fit in the Ripper... so should I cacel the order quickly and find something 540 size?

Jwalk33

Foxy

Yes. That's a 1/8th motor

jwalk33

Hi,

I'm just going to keep the motor for now incase I convert my 1/8 scale buggy into electric someday, or buy something that can handle it.

At what Amp and Voltage should I charge a 6 cell 2400mAh NICD pack?

Same for 6V 16mAh 5-cell hump reciver pack?


Thanks,
Jwalk33

Foxy

Try the 2200 at 4A, if it gets hot, go down to 3.

Do the receiver pack at 1.5a.

jwalk33

How many volts ?


Thanks,
Jwalk33

jwalk33

It will only allow me to discharge @ 1.0 volt, and I'm not sure as to how many amps I need to discharge at.



Jwalk33

BKoz559

My Feedback: (3)

Discharge at the same rate as the charge and watch out for heat. If it gets hot then lower the amperage.

The 1.0v is a cutoff most likely. Meaning that the charger will bring the pack down to 1.0v per cell. For the 6-cell pack that would be 6 volts total which is a safe discharge voltage. You can go to .9v and still be safe.

jwalk33

Ok, I meant that it will only allow me to discharge at 1A.

So apparently 1A for discharge and @ how many volts? I really hate to be bothersome, I've just never used a charger like this so I apologize.



Thanks,
Jwalk33

BKoz559

My Feedback: (3)

If the charger can only discharge at 1A then that's all you can do. You can leave the voltage at 1V. Depending on what type of pack you're discharging (6 or 7 cell) the charger will stop discharging once it detects either 6 or 7 volts coming off the power leads of the battery.

jwalk33

What exactly is a UBEC ?


Thanks,
Jwalk33

BKoz559

My Feedback: (3)

Universal Battery Eliminator Circuit

It's a device that taps power directly from the battery and regulates voltage to a specified level, usually 6V, to power onboard electronics. Why not use the ESC's BEC? Because sometimes the ESC can only supply up to a 5A. Most of the time this is sufficient, however, if you have super powerful or high speed servos, they can draw more current than the ESC can supply so a separate power source is required. Otherwise your ESC will shut down all the time or worse yet, burn out.

jwalk33

I was just asking, I did a bit of research but was still not clear of its purpose.

I will be using the ESC's UBEC in hopes that it has one built in.



Jwalk33

Foxy

It will have a built in one, 90% do.

A separate BEC is rarely required, but is always a good idea for any electric model, it takes a great deal of strain off the ESC.

jwalk33

Thanks Foxy,

So should or should I not worry about investing into one for my Ripper ST?




Jwalk33

EXT2Rob

My Feedback: (1)

For your truck, I don't think I'd worry about it.  A receiver isn't going to take much juice.  The servo can, but in your light truck, I doubt it's gonna pull much current.  The built-in BEC should be perfectly fine, unless you end up using a power-hungry servo, or a "high-voltage" servo. (There seem to be a raft of new servos coming out that can run off 7-8volts.  I guess with the idea that they can run DIRECTLY off the main battery.)

jwalk33

Ok thanks!



Jwalk33

jwalk33

Hi guys,

Does anyone have any ideas as to how I can lock the slipper clutch on the MRP Ripper ST? I just put a faster old brushed motor in it and it slips really bad even though I have the tension/slipper spring tightened all the way.

I only imagine how bad it will once I put brushless system and lipo battery in it.


Thanks,
Jwalk33

Foxy

The pad must be done. If its still slipping when screwed in all the way, there ain't a whole lot more you can do. Change the slipper pad.

jwalk33

It only slips for maybe 2-3 seconds. Is there a way I can just remove it, or get a stronger spring ?

EXT2Rob

My Feedback: (1)

Ya don't wanna do that, mate. The slipper is there to protect your drive train. But it just sounds like the pad has either glazed, or is just used up. Get another!  They're cheap.  You could try taking some sandpaper to the slipper pad, to take off any glaze, but chances are it needs replacing.

jwalk33

ok I'll just replace it. I wonder if I could upgrage it to something of better quality. I was told that this thing is the exact same as this by a Team Associated rep.


Jwalk33