Cheap MRP Ripper ST
#26
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RE: Cheap MRP Ripper ST
ORIGINAL: jwalk33
What I think I should've done was get a lower kv motor around 1500kv-2200kv small pinion and bigger spur. Wouldn't this give hi speeds while also reducing the most strain on the motor thus reducing heat issues, vs going with bigger pinion and smaller spur ?
I guess I can order a lower kv motor as described above as well as pinions and spurs.
What are you guys thoughts on this, maybe I tottaly screwed up here? I'm not looking for the most powerfulest/fastest bottom-end... more like a desent bottom end and fastest top end possible.
Thanks,
Jwalk33
What I think I should've done was get a lower kv motor around 1500kv-2200kv small pinion and bigger spur. Wouldn't this give hi speeds while also reducing the most strain on the motor thus reducing heat issues, vs going with bigger pinion and smaller spur ?
I guess I can order a lower kv motor as described above as well as pinions and spurs.
What are you guys thoughts on this, maybe I tottaly screwed up here? I'm not looking for the most powerfulest/fastest bottom-end... more like a desent bottom end and fastest top end possible.
Thanks,
Jwalk33
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.
#27
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RE: Cheap MRP Ripper ST
ORIGINAL: jwalk33
I orderd a 120A ESC, 9T 4370kv motor and 2200mAh 2S1P 45C lipo.
Thanks,
Jwalk33
I orderd a 120A ESC, 9T 4370kv motor and 2200mAh 2S1P 45C lipo.
Thanks,
Jwalk33
#28
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RE: Cheap MRP Ripper ST
Thanks BKoz559,
I understand what you saying which makes total since. Especially using the 10 speed bicycle analogy, very well put!
I think I will start with stock gearing as you suggested, and eventually a lower kv motor and bigger pinion/smaller spur.
With the ESC, Lipo, and motor... do you foresee any issues, i.e. the motor draining too much from the battery, or one device consuming or being neglected of voltage ? I'm not talking about these issues to be caused by improper gearing, more specifically incompatible amounts of power.
Thanks,
Jwalk33
#29
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RE: Cheap MRP Ripper ST
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.
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.
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RE: Cheap MRP Ripper ST
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
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
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RE: Cheap MRP Ripper ST
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
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
#36
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RE: Cheap MRP Ripper ST
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.
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RE: Cheap MRP Ripper ST
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
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
#38
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RE: Cheap MRP Ripper ST
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.
#40
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RE: Cheap MRP Ripper ST
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.
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.
#41
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RE: Cheap MRP Ripper ST
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
I will be using the ESC's UBEC in hopes that it has one built in.
Jwalk33
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RE: Cheap MRP Ripper ST
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.
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.
#44
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RE: Cheap MRP Ripper ST
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.)
#46
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RE: Cheap MRP Ripper ST
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
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
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RE: Cheap MRP Ripper ST
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.
#49
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RE: Cheap MRP Ripper ST
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.
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RE: Cheap MRP Ripper ST
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
Jwalk33