math help Plz.. Shadow specifications

[Rocksalt]

I have the datasheet for the shadow motor. 1st question is....
what is the max sustained RPM of the motor? The data sheet shows hp 220 25,000 1/min. Or the HP220 S:70,000 1/min. The data sheet tests show
voltage at 7.8V
40.8 amps,
watts in at 317.8,
watts out at 271.5,
efficiency at 85.5,
torque at 5.7nm, 4.12ft. lbs@ 45538.9 RPM,

Peak torque @ 38986.4 RPM @ 9.7nm or 7 ft. lbs. torque @ 64.7A, HP 52.99! *** again (v=7.3, input watts=469.9, current=64.7, efficiency=84.2, power factor=.574)

Using these numbers I calculated the PF to be .576(watts/(1.732*E*I)

Now I want to calculate the HP. (1.732*E*I*EFF*PF)/746 :36.387HP ***
Even if I use the specs for DC HP (E*I*EFF)/746 I get 36.47 *** again

I also calculated the resistance(yes, I know, a motor is not considered a resistor due to back EMF). At 7.8V the resistance is .19ohms. At 7.3V the resistance is .11 ohms. At 6.2V the resistance is .11 ohms.

Efficiency=(746*HP)/(1.732*E*I*PF) (3 phase)
EFF=(E*I*EFF)/746 (DC)
PF=watts/(1.732*E*I)
Current=(746*HP)/(1.732*E*EFF*PF) (3 phase)

Using the values obtained and using them in the different formulas results the same numbers.(checking work).

I know this may sound dumb.. but I wanted to run the motor at 14.8V, set the rev limiter, and see what the difference is in performance. I just wanted to make sure the watts did not exceed capacity of the motor, thus burning it up. I was hoping if I did run 14.8V that I could run a much larger pinion and achieve new speeds while keeping the low end grunt.

What is confusing me also is that I want to buy a lower kv motor and run 14.8V. I cannot exceed 100A of the controller and I cannot exceed the RPM of the motor. In doing this I would need a gear ratio that will allow this. What would the result be in terms of power at the bottom and top?

I wish I could adapt a 2 speed to this car(xxx-4), then I would be able to finess the right outcome. Yes, the car cannot handle speeds greater than 50-60mph. I don't care about this right now. The drive train losses are not that significant with this car. No, it's not for racing. I am just playing with currents, voltage, and gearing to obtain high speeds. I will worry about the cars ability to handle this speed later. I might even adapt this motor for use in my 1/10 serpent if I can find a spot for the batteries.

With the serpent I was running an RPM of 40,000 and about 50-60mph depending on gearing. I want the same from the electric motor. I can just run 2wd with the serpent to help with reducing the loads.

The controller I have is the Schulze U-force 75. Batteries are 4s lipo 8000mah.

[Rocksalt]

ok, I think I know where I might have screwed up... I don't have the values for the AC voltage to the motor at specified RPM. Unless it's not stepped up or down internally, it should be close though. Obviously I am missing something here. If anyone has picked up the ball I dropped, please chime in.

[kufman]

I dont think the data sheet gives any A.C. numbers at all. P=I*V = 40.8*7.8V = 318.24 W. Take that times .85 (for the efficiency) and you get 270.5 W

270.5/745.7 = 0.362 HP.

Running the shadow on 4S would be dumb. It will blow up the motor and possibly the controller. going to a lower rpm motor is the only way to do it. Using the rev limiter is not a nice thing to do, it is very abrupt. is you want to run 4s go to a motor that will be around 45,000 rpm on 14.8 volts... so 45,000/14.8 = 3040 rpm/v. It will still be more powerful since there will be fewer losses due to high current. P_lost=(I^2)*R If you double the voltage and lower the current to 1/2 of it's original value, your P_lost wil be 1/4 of its original value. The ESC will stay cooler and the use of huge wire on the motor and controller is not necessary.

[Rocksalt]

I missed the damn decimal point for the efficiency!

How about the lehner basic XL3600 on 4s(97 amps, 1300 watts)? Or go with the 3100(1300 watts, 80A).

[kufman]

i would say the 3100 would be better, but I don't know if it will fit in the car. The XL series of motors will push the u-force to it's limits. Maybe a regular basic 3100 would be the ticket.

[Rocksalt]

In order to convert my 1/10 scale serpent to elect. I need 1.5-2hp. I raced that car with a .21 in it. I converted it to .21 to see what it would do against the 1/8 serpent's. Those engines are 3.5HP 60KRPM. The .15's we used were 40K-55K @ 1.5-1.7HP. I have already looked at it and it will fit nicely in that chassis. I even have a spot for an 8000lipo. It has to have the power, and I can use it no problem. It would be nice to use in the 1/10 xxx-4, but that drivetrain won't handle it. I may use something with a bigger shaft for that car as well. Maybe the standard .15 engine size so I won't have to change much with the 2 speed pinion setup.

[kufman]

ya in that car you can go to a larger motor. HP number can be alittle tricky to convert. 1 HP of electric motor power usually seems like a lot more power than 1hp of gas power because of the torque. You might be able to use the lehner XL motors, but I think it will be rough on the U-force. Definately put a fan on it if you decide to try it. I have run my u-force in my e-maxx but I was only using a Feigao 10L (2480 rpm/v) on 12 cells. I used that same setup in my 1/8th buggy conversion and it was just as fast as the Hyper .21 that the buggy came with. Just be careful when you try stuff and you should be good to go. Keep track of temps during the run.

[TimisTim]

The UF75 WILL NOT HANDLE IT. I used mine in the early stages of testing on my MT2 while it was still in stock form on a xl3600 on 3S. Motor ran great but the controller had it at about 5 minutes of normal bashing driving. This was with a (I think) 5 volt fan doing overtime with the 11.1v battery.

I would reccomend something like the Mtroniks truck/Quark 125 monster/MGM16016 (but they are terrible controllers)/BK 12020 or 9920......all of these can run 4S if you wish and on that voltage should turn your xxx-4's drivetrain to ashes in no time :)

You both seem plenty smart when it comes to electronics so I will say to not forget your batteries. Make sure they are up to the current capabilities. 1300w is alot!

[Rocksalt]

The UF75 WILL NOT HANDLE IT. I used mine in the early stages of testing on my MT2 while it was still in stock form on a xl3600 on 3S. Motor ran great but the controller had it at about 5 minutes of normal bashing driving. This was with a (I think) 5 volt fan doing overtime with the 11.1v battery.

Question... Did the controller burn out, or just thermal? Did you connect the 5V battery to the source voltage or the power input of the reciever?

I think the MT2 is alot different than the serpent impact 1/10. That is a nice free rolling car. Did you try and reduce the pinion to see if you could just unload it a bit? Something that doesn't make sense about the lehner motors is there are several motors with the same wattage, but show less amps. Math wise it makes no sense. I see now the schulze is rated for 12C. This is 14.4V :( I wonder how it would like 4S @16.7 when fully charged?!? 38750RPM on the 3100xl is not enough on 3S, unless I can gear it out, but I think the loads would be to much.

I have not a clue as to how much the current spikes would get on a high grip track running foam and the serpent. Shoot I don't want to buy ANOTHER controller.

Anyone want to buy a schulze, lol

[TimisTim]

All it did was thermal. My fan is wired in line with the controllers battery wires. I tried 10, 12, and 14t pinons and sprs from 49-53. It did get better with short gearing. I just dont think there is a way to get any long runtime out of it with that motor.

Im not sure on the car you are running it in, but why run an XL to begin with? Why not get a shorter/lighter motor with more snap.

[Rocksalt]

To be honest, I am not savy to the different can's, shaft sizes, etc. that's why I am here, to read and learn a little. Opinions welcome, wanted, and much appreciated!

I am alomst satisfied with my xxx-4. I could use more top speed, but I am close to what I want.

My new project is to convert my gas powered serpent 1/10 impact to electric. I really would like 3hp elect in it. To get the best of both worlds I would like the can to fit in the xxx-4. The only real weak spot is the small width belt. I run o-way front and a locked rear. It just suits my driving style with 4wd. Been racing that way for awile. The serpent is a GREAT car. It's leaps and bounds above many other 1/10 scale cars. I have been out of the racing scene for about 5 years now and things have changed a little. I am not hip anymore to what's good and solid so I am working with what I have. It's sitting on the shelf anyway, I need to use what I have as it's a great car.

If you have any advice on a motor talk away! I am still pursuing getting a motor with 1200 watts. This is the 1.5HP mark I need at minimum(or so I think). I didn't realize I couldn't run the schulze on 4S or didn't think of it. I might have jumped the gun on that purchase. It works very well in the xxx-4, so I may just keep it. Still would like a motor with a little more power than the shadow.

[TimisTim]

Well the best motor for the money I have come across for 1/10 4wd is the Feigao 8s. You run that on your UF75 with a fan and 3S and you will be plenty happy.

[Rocksalt]

Well the best motor for the money I have come across for 1/10 4wd is the Feigao 8s. You run that on your UF75 with a fan and 3S and you will be plenty happy.

What is the exact number of that motor and the specs/place to buy? Do I need any adapter plates for it to work in the 4wd? Would it be more powerfull and faster than the shadow?

[TimisTim]

Im not familiar with its numbers except that it has a kv of about 4500. No adapter plates needed. I just know that I have ran it in my xxx-t on 3s and it didn't thermal my UF75, or the motor itself on 20/82 gearing. It runs alot cooler while having more power than my lehner 4200 on the same gearing. I have tried to regear the lehner but it just won't cool down. This was on 2s lipo. There are faster more efficient motors out there like the pletty's and the lehners but they are quite pricey. You might want to try the plettenburg extreme motor its a 4 pole and suited for off-road. I don't know where to find one but start at starluckrc.

[Rocksalt]

is it the 380 or a 540? I already looked on the starluckrc and didn't see it. Blind today :(

[tcolesen]

It is a 540. I can't find the Feigao 540 8s in stock, but RC-Monster does have a Wanderer (pretty much the same as Feigao) 540 7s in stock:
http://www.rc-monster.com/proddetail.php?prod=BKWAND_S&cat=20

Getting 3HP (2238Watts) out of a brushless motor for 1/10 is RIDICULOUS. 3HP would be way too much for even the toughest 1/8 scale (buggy/truggy) drivetrains when with an electric motor. The teeth on the gears would just shred from the massive torque. Besides that, there's no way you could fit enough batteries to provide 2200Watts+ for any decent amount of runtime into a 1/10 chassis. You'd need 22 NiMh cells (1.5kg, ~3.2lbs) to provide that sort of power, and even that would only be peak power!

[Rocksalt]

tcolesen, Thank you for the link.

I raced on-road 1/10 impacts about 5 years ago. The Novarossi motors we used were rated stock at 1.2hp(IIRC). We ran the outlaw motors with modified cranks. I also raced the Kyosho MP5 with a picco 3.5hp .21. I modified the belt system in the Impact to use the 1/8 vector belt. The car was a blast to drive. I could smoke the 1/8th scales on the straight. I took the 1/10, used a lola body, outlaw motor(.15 rossi), threw a diff in it and raced 2wd against 4wd, and won a 20 minute main against some very good drivers. Unless the HP ratings are phony from those motors, I was using the power. The impact is a strong car with great high speed stability.I don't need .21 power in the 1/10th, But I would at least want the 1.5HP to make it equal what it had in nitro.

I was looking at some battery specs today at maxamps and discovered what you said about the batts. Looks like the best I can shoot for is the 97A constant discharge 8000's or 10,000mah batts. No problem. That's 1119watts. 97A available is 1164watts@12V. 1076watts available at 11.1. At 4S I can get only 1590watts/2.1HP.

You are right, 3HP is not gonna happen.

Were the advertised HP rating from novarossi, mega, rex, picco, etc. , inflated? If they were, then at least I can get 1.5HP out of the schulze at 11.1V.

What do you think?

[TimisTim]

HP ratings are different for electric and nitro motors. Im not sure why. I have seen 16v brushless systems outrun 3hp nitros in identical trucks (aluminum maxx's). Theoretically the motors wouldn't be equal but the "paper underdog" wins. It proabably has someting to do with how the power is delivered i.e. no powerband in electrics and a constant torque.

Realistically though, in your setup, the fastest/most efficient/easiest on equipment combo would be either the 380c-9t or the 8S both by feigao on 3s lipo. Both would spin just shy of 50,000rpm's (though they do tend to rate their motors higher than what will be achieved under an honest load). I still stand behind my 8S as being the best 1/10 2wd ST 7.4v bashing motor, its just very versatile.

[tcolesen]

TimisTim is right. However, the BIG difference between nitro vs. electric is TORQUE. Electric motors are farm more capable of putting out larger amounts of torque than nitro engines. In fact, if you had a power supply that could supply an infinite amount of current and a speed control that could do the same, a brushless motor could theoretically put out an infinite amount of torque. This is because the amount of torque that a brushless motor puts out is proportional to the amps it pulls. For example, let's say that your vehicle is under heavy acceleration (lots of traction). A nitro engine might bog out, but an electric motor will push through the situation by pulling more amps. If the batteries can't supply the amps that the motor is pulling, then their voltage will drop.

For this reason, you can't effectively compare nitro engines and electric motors quantitatively.

[Rocksalt]

OK, I'll go along with that. Would you say the 1.5HP would be a nice upper point for the serpent in terms of gauging the 2 motors? It seems that I can get a system that can make that power with current batteries(pun intended). I wonder what wind would be appropriate for this application.

[tcolesen]

How much money are you willing to spend? If you want to get top-notch motors ($200+), you can get the Lehner motors. They are more efficient overall, and also more efficient at lower throttle than any Feigao motor. They would also help you get closer to 1.5hp, if you are set on that.

[SpEEdyBL]

Why do you need 1.5 horsepower? I guarentee a 700 watt (~1 horsepower) brushless motor will outperform any 1.5 horsepower nitro engine. In fact, when a motor is rated at 700 watts, that's not the max power output of the motor. It's more of a continuous rating that has to do with the motor overheating or mechanical failure. Theoretically, max power output of a motor is VI-RI^2-IoV. Take a 380 12s for example. R= .0212 ohms Io = 1.5 amps. Run it at 14.8 volts constant. Peak power is 2560 watts at 350 amps! But motor is only 50% efficient so it will heat up almost immediately. However, you would never see that amount of power in real life because no batteries can supply 350 amps without the voltage dropping. So really, your batteries are the main factor in determining horsepower, not the motor. Btw, any applicable motor for 4s is much more powerful than any 2s setup, so if you've never tried 4s before, your in for a big surprise. The biggest motor for you that I would recommend would be the feigao 540 12s. It's rated for 900 watts continuous.