Darn...no over-volting the Monster

[suicideneil]

It seems to be a bit of a common mis-conception that higher voltage = more insane power and speed, and it simply isnt the case. Higher voltage can mean that, certainly, but what it really means is a slower turning motor can be used that leads to longer run times, lower temps, and cheaper batteries. The only downside I can find is the need for more space on the chassis for batts maybe, and a higher voltage capable charger maybe too- no biggie.

[lincpimp]

Originally Posted by SpEEdyBL

That doesn't explain why 6s wont be enough. All your saying is that 12s is better than 6s, while you don't prove how much of an advantage there actually is (where is your actual data?) Not everyone is trying to break the land speed record with a monster truck. I would be more concerned about lipo failures than having a setup that runs 20 degrees cooler than what is already acceptable. The more cells there are in a pack, the more vunerable the cells are to undervoltage, since a weak cell has to go way below the safe limit before the mean voltage of the cells in the pack triggers the cutoff.

Ok, I will say that for most situations that 6s would be fine in a mt geared for around 40mph. Given a sytem properly setup for 6s and another that has a motor with half the kv on 12s, the 12s setup will pull half the amps that the 6s does, and produce more torque. Plus the batteries can be half the capacity and provide the same runtime (most likely more). I am sure that a expernisve motor in a hv setup will run cooler, but not so cool as to fail. Most find a feigao xl to be ineffiecent, and heat up to much, such as a 7xl on 4s. I run a 14xl on 8s lipo and it performs fine, in a heavy savage, and I use a 60amp air esc that barely gets warm. Plus I can get away with 12c lipos, my 3600 polyrc lipos only cost 120 bucks (30 each for 2s 3600 12c packs x 4). I would love to see another 120 dollar lipo compare to this setup in either 4 or 6s. The lower loads placed on the cells by a hv setup will help the cells stay in balance. High current draw is what causes cells to come out of balance. Hv just makes sense for larger,heavier vehicles. More torque, less load on the battereis, and cooler running with cheaper equipment. For me hv is the only way to get a feigao to work properly, but then they are great value!

[lutach]

Originally Posted by suicideneil

It seems to be a bit of a common mis-conception that higher voltage = more insane power and speed, and it simply isnt the case. Higher voltage can mean that, certainly, but what it really means is a slower turning motor can be used that leads to longer run times, lower temps, and cheaper batteries. The only downside I can find is the need for more space on the chassis for batts maybe, and a higher voltage capable charger maybe too- no biggie.

There are good and inexpensive chargers out there already. I charge my 2 5S Thunder Power packs in parallel using my AF 109. The current electric conversions are the ones putting limits on the batteries used. I showed suicideneil my chassis designs and they'll be made for HV application. You can easily fit 12S in them and if you think 12S is too much, just use 6S. It will be a well balanced chassis.

[johnrobholmes]

I would be hard pressed to qualify HV as better, but I can certainly recognize the benefits of 1/2 the amp draw and need for less battery capacity at a given power level. Whether or not a given motor runs more efficient at higher voltage/lower KV is beyond my knowledge, and I would love to hear what Mr. del Castillo has to say about it.


I illustrate the point though, in one of my rigs I run a 10t brushed motor. It takes a 4200 mah 15C pack just to bear the load. If I drop down to a 19t it spins half the speed, I can use twice the voltage, and a 2100 15C pack nets the same runtime and punch. Batteries cost the same, but the whole system does run cooler. 6s lipo on a 19t will be pretty fun for a rock racer.

[SpEEdyBL]

There is one thing that a few of you need to understand before you can tell me that I "don't get it"

First off, motor resistance goes up by the square as kv reduces. For example a 1000 kv motor will have four times the resistance as a 2000 kv motor of the same design. Energy loss through heat is (resistance)(amps^2) so even though you may be drawing half the current to get a given power output with the 1000 kv motor, the same amount of energy is being wasted as heat as the 2000 kv motor when it is drawing twice the current.

The same is true with batteries. If you have a 4000 mah 6s pack, it will have 1/4 the resistance as a 2000 mah 12s pack because each 2000 mah cell has half the resistance as each 4000 mah cell and there are twice as many 2000 mah cells in series. So again, even if you are useing half the current with the 2000 mah 12s pack, you still get the same amount of heat as you do with the 4000 mah 6s pack.

This also applies to escs. You will get the same amount of heat with a 100 amp esc that can handle 12s verses a 200 amp esc that can only handle 6s, because in order for the 6s esc to be rated a 200 amps, it must have fets that are 1/4 the resistance as the fets used in the 12s esc.

Wires? Use 1/2 the guage and/or shorten them and your set.

I admit that in reality, 12s will run cooler because it is difficult to change all of these factors at once. And in reality, high turn motors are wound better because smaller gauge wire is used.

One last thing. Some of you are saying that "lower kv motors have more torque." That is a very ambiguous statement because that is only true under certain circumstances. That just like saying 12x4 is bigger than 8x6 because 12x4 has a 12 in it. Because kt is directly inversely proportional to kv, the 1000 kv motor will have twice the torque PER AMP as the the 2000 kv motor, but since the 1000 kv is pulling 1/2 the amps, it will have the SAME torque as the 2000 kv motor.

[DrKnow65]

Speedy, I'll let the Electrical Engeneers chime in here, but I do not argee with your math.

While you are correct about the "internal resistance" being half between the 2000kv and the 1000kv, that is not a direst equation to what you get in watts lost as heat. I will not get into thermo dynamics, but here is an example, the entire car industry, all around the world, switched their electrical system from 6volts to 12 because it made the components last longer and not heat up as much. Amp draw is what creates heat in a circuit, not voltage or even watts. A 120,000volt power line is not hot without a load. Less amps is less loss, that is a fact.

[lutach]

SpEEdyBL,

Not only we have a few members here and myself, who are running HV, we can back any statement said. We have real world experience and I can't find where the heat is generated to cause the same loss you've mentioned. From what I know (I'm not an engineer) when electronics are subjected to high heat, they become less efficient and that can be seen in any Electronic Component being Active, Passive, Electromechanical and Interconnect. Look at some datasheets of and you will see that a MOSFET will perform better at a cooler temp. then at a higher temp. The only thing that I've seen perform good when heated to a safe high temp is lipos. SpEEdyBL, have you done a HV conversion? If not please do so, but thinking of a speed machine, but a well geared racing set up. BrianG's calculator is a great tool and I use it a lot. Now John knows how a high turn motor acts in producing torque in rock crawling. I would like to see how a high Kv motor does in rock crawling.

[lincpimp]

Not being an enigineer at all, I had the same view about the benifits of hv. Heel, I bough my first lipo chargwer thinking there was no way I would ever go past 4s lipo. Well, I have built many vehicles, and even going from a 4s to a 5s setup makes a world of difference to me. I have done afew 6s setups, but have not really tested them much, as my quark escs are not too fond of 6s, but the MMM should help with the testing.

I have the 8s savage, and a 4s revo. The savage is heavier than the revo, both run the same diameter tires. The revo has a 7xl, the savage has a 14xl. So kv on the revo is 2300 or so, and the savage is around 1200kv. I run 3600 12c lipos in the savage and 4900 25c lipos in the revo. The revo produces more heat, on the motor and esc. The savage gets to about 140-150 on the motor, esc does not get more than 110. Depending on how hard I run the revo, the esc will thermal, and the motor can beat 160. Te revo has more airflow over the equipment than the savage too. Most people have heat issues with the feiga motors, they are cheap, so you get what you pay for, IMO.

Is there a specific reason that you do not like the idea of a hv setup? I find that the lipos are not pushed as hard, and therfore have more punch longer thru the run. This and lower temps are the main things I see with the hv setup.

[johnrobholmes]

I actually prefer a lower turn motor for crawling with more geardown. While higher turn motors produce more torque per amp, they also pull less amperage so for any certain speed the power is a wash. Most people run 55t motors because they have enough power and are the right speed for our average geardown (and they won't smoke as fast under a stall). I run motors about three times as fast, gear down as much as possible, and volt up so high that few of my crawlers can actually pass as crawlers anymore :D

I am actually doing a test to see which motor wind has more torque at given loads and voltages. I have a feeling there there will be a sweet spot for each motor where it will have the best torque under said load if the batteries will handle the amp draw. With a fixed geardown my suspicion is that a low turn motor will perform better at low loads, and high turn motors will perform better at higher loads. This is because the batteries will be a limiting factor. At any rate I do know that 540 motors of similar build are all about the same power no matter what the wind (within reason) if volted to the same RPM.

[SpEEdyBL]

Actually The main reason why I am not in favor of an hv setup is that I don't have enough money to buy one since im still a college student! I know kind of a lame reason.

But anyhow, lincpimp. nice info. Part of the reason why the 7xl is overheating more than the 14xl could be that your 4s pack holds its voltage better at twice the current than than your 8s pack, which would also explain additional esc heat too. A fairer test would be to put two 4s 3600 12c packs in parallel and run them with the 7xl. If you want to compare escs the higher voltage one has to be the same brand with half the amp rating. Then again, you also have to adjust the wire guage appropriately.

Also I have owned five differnt feigao motors: 540 6s, 380c 9t, 380 12s, 540 8xl, 540 9l, and my findings have been random. The 380c 9t always ran coolest on 6-7 cells ni-mh, and ran hotter on 3s lipo, but still within an acceptable level, while the 380 12s ran coolest on 3s (still hotter than the 9t on 3s) and could even not be run on 6 or 7 cells nimh without seriously burning my finger. Weird huh and ive tested different gear ratios with the same results. So it's my speculation that the voltage and current needed to keep the motor cool vary from motor to motor, or that it's the luck of the draw whether you will get a good feigao motor. My 540 9l in my 8ight btw cannot be run on 3s no matter what gearing and overheats the MM too, but it can run for a longer period of time on 4s. Other people that I have heard from claim that the 9l runs just fine on 3s.

Again, I've never denied that higher voltage is better, but where comes the point were a 6s setup can't be used? If that point is beyond what 95% of the people are looking for, then I find it a little rude to beg Castle to begin making 12s system while they are still working their a** off to get their 6s system that many people have been waiting for ages, out to the shelves, thats all.

[lutach]

Originally Posted by SpEEdyBL

Actually The main reason why I am not in favor of an hv setup is that I don't have enough money to buy one since im still a college student! I know kind of a lame reason.

But anyhow, lincpimp. nice info. Part of the reason why the 7xl is overheating more than the 14xl could be that your 4s pack holds its voltage better at twice the current than than your 8s pack, which would also explain additional esc heat too. A fairer test would be to put two 4s 3600 12c packs in parallel and run them with the 7xl. If you want to compare escs the higher voltage one has to be the same brand with half the amp rating. Then again, you also have to adjust the wire guage appropriately.

Also I have owned five differnt feigao motors: 540 6s, 380c 9t, 380 12s, 540 8xl, 540 9l, and my findings have been random. The 380c 9t always ran coolest on 6-7 cells ni-mh, and ran hotter on 3s lipo, but still within an acceptable level, while the 380 12s ran coolest on 3s (still hotter than the 9t on 3s) and could even not be run on 6 or 7 cells nimh without seriously burning my finger. Weird huh and ive tested different gear ratios with the same results. So it's my speculation that the voltage and current needed to keep the motor cool vary from motor to motor, or that it's the luck of the draw whether you will get a good feigao motor. My 540 9l in my 8ight btw cannot be run on 3s no matter what gearing and overheats the MM too, but it can run for a longer period of time on 4s. Other people that I have heard from claim that the 9l runs just fine on 3s.

Again, I've never denied that higher voltage is better, but where comes the point were a 6s setup can't be used? If that point is beyond what 95% of the people are looking for, then I find it a little rude to beg Castle to begin making 12s system while they are still working their a** off to get their 6s system that many people have been waiting for ages, out to the shelves, thats all.

It's not that we are begging. Patrick said he would do 2 versions a few months back. Plus Castle needs to fill that gap to add a HV car controller so we (The ones who likes HV) can have a US company with one.

[BrianG]

I think HV is better... but it depends.

If you're just racing, or bashing at reasonable speeds, there really is no reason to go any higher than 6s. Even at a "low" 75A, that's almost 2.25HP! Unless your truck is especially heavy (~12lbs+), I can't see much advantage. Sure, you can use lesser batteries since current consumption is lower, but you still need quite a stack of them. Also, simply mounting them can become an isse with 8s+. Finding a charger/balancer setup that will do over 6s gets expensive too. Chargers/balancers that can do 5s-6s are very common.

However, if you need as much power as you can possibly get, then HV is a no-brainer. How else can you get 5HP+ while keeping currents reasonable? To me this would only apply for the heavier trucks or for the high speed freaks.

To me, any setup that will take over 100A sustained bursts should go higher in voltage.

[TexasSP]

What about HV for the 5th scale conversions that are popping up as well. With the wattage needed to move such a large vehicle, one will need hv to do it efficiently. I know many have used substitute controllers (ie: plane and heli ESC's), however, a purpose built hv controller would definitely be best. I also personally think that in 5th scale, a high performance electric system will be no more costly than a high performance gas system. Seeing the money the 5th scale guys put into the high end motors, getting them customized, $200 plus tuned pipes, and so on, electric seems a lot more reasonable.

[lincpimp]

Originally Posted by TexasSP

What about HV for the 5th scale conversions that are popping up as well. With the wattage needed to move such a large vehicle, one will need hv to do it efficiently. I know many have used substitute controllers (ie: plane and heli ESC's), however, a purpose built hv controller would definitely be best. I also personally think that in 5th scale, a high performance electric system will be no more costly than a high performance gas system. Seeing the money the 5th scale guys put into the high end motors, getting them customized, $200 plus tuned pipes, and so on, electric seems a lot more reasonable.

Yep, a 350 dollar motor, 300 dollar esc, and 450 or so worth of batteries would make a 1/5 scale scream! 1100 bucks well spent. I really want to do a large scale build, but the lack of a purpose built car hv esc is stopping me.

[TexasSP]

Alright Patrick, get this ESC made so linc can make an extreme 5th scale for all of us to envy. (also so we can make him do all the hard work and then just copy what he does)

SO at 1100 you are right in range of what guys spend on high dollar gas motor setups, and some even spend more.

I would love to have a 5th scale F1, I just don't want gas. While I know it's not like the irritations of tuning and upkeep of nitro, I still don't want the mess and the noise.