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DeeMiller

Rotation direction of Sport Tuned motor.

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Sport Tuned motors have a fixed rotation direction.

If I change the + and - (i.e. change the rotation direction), how much power do I loose?

Is there are way to compensate this?

 

Dee.

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Not that much as far as I am aware - there is no advanced timing on them. I find that its a little top end which is often why I reverse the diffs on my TB01 to suit that better going forwards but this is with a 540 stock - when using a sport tuned I find it very little bother which way its going.

besides direction of best rotation should be set for the car to go forwards anyway.

Best regards Ryck  

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Thx Ryck.

I noticed the slightly higher top rpm too when reving it the way it's supposed to run.

Anyone more ideas?

 

Dee.

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Yeah - Tho for some reason this always seems to be reverse for me lol.

Simple way to solve this is to slip the direction of the diff around. So if the diff gear is to the right on the TB01 according to the kit so its to the left now for max power. I know its not by the book but runs all the same - Tho I know some cars (TT01) cannot perform this function.

For what car is the sport tuned?

Best regards Ryck  

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For what car is the sport tuned?

I could tell you but then I have to kill you (my other hobby)...

 

Dee.

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kk lol - I will say this only once with the madonna and the bigga ..........

well hope that helps as long as its nt a race touareg 2 [;)]

cheers Ryck  

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Not that much as far as I am aware - there is no advanced timing on them.

Am not sure on that, especially on the 27T version, as why would they otherwise unlike a stock 540 have a recommended direction,, higher speed in that and red/black wires?

Dee, would better get a motor with zero or adjustable timing before running it reverse, not only speed will be lower, but also efficiency and there might be high brush sparking and wear, anyway ST isn't really anything special.

Cheers 

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PICT0032.jpg

Well, looking at my modified motor, to increase power, the endbelt can be turned counter-clockwise to about 20 deg.

As ingnorance is a great invention, I did the same on the ST.

PICT0033.jpg

I mounted the ST into a motor mount and adjusted the endbelt with a tool (needs a bit of force though, it's press-fitted in the can).

Guess what?

It runs a lot faster in reverse.

It may be my imagination but it runs even faster than "normal fwd"...

Now I'll fine tune the modified "reversed" ST to run as fast as a stock ST.

How am I gonna do that?

An electro motor works like a generator so:

I will connect a standard motor to the axle of  the stock ST and a voltage meter on the standard motor.

The higher the revs, the higher the voltage, right?

This value must also be set to the modified ST motor...

Any other suggestions?

 

Dee.

PS You may wonder why I want to do this but it all will clear up in a few weeks, it's too soon to make any conclusions yet.

 

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though, it's press-fitted in the can).

Gues what?

It runs a lot faster in reverse.

It may be my imagination but it runs even faster than "normal fwd"...

Now I'll fine tune the modified "reversed" ST to run as fast as a stock ST.

How am I gonna do that?

An electro motor works like a generator so:

I will connect a standard motor to the axle of  the stock ST and a voltage meter on the standard motor.

The higher the revs, the higher the voltage, right?

This value must also be set to the modified ST motor...

 

Yes, a motor used as a generator can give you an index of its rotating speed, at least qualitative one. But, you shouldn't increase timing only according to speed as after a angle value efficiency drops alot and even 2 same motors vary in speed (production tolerances) and a stock motor used as a tacho won't give you very precise indication of small speed changes, you better should also connect an current meter (ampmeter) and increase timing to the point where current rises quickly.

Other then that if a stock Sport Tuned really has 27° timing, I would turn the end bell to its symmetric position, i.e. 54° back to -27°.

Modern motors don't really need running it, but since you are using it in reverse and brushes and commutator might need to bead in for this new direction I would let it run with 6V-7.2V for some minutes without any load.

Cheers 

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Thx Theo, that's a very constructive reply.[Y]

I'll also use a current meter as much as I use my eyes (sparks) and ears (noise) so it should work out ok this way...

I'll update when I got them ready (i.e. if it works).

First I have to check if the standard motor (stock 540) has identical values, CW and CCW (by using another stock 540 forward and reverse power).

Then I'll set both the ST-motors to equal voltage values (digital meter: +/- 0,005V tolerance) and recheck with the current meter (tolerance +/- 0,005Amps or 5mA).

 

Dee.

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PICT0034.jpg

Calibrating a standard  RS-540 SH motor.

"Forward" power: > 6,30V (increasing as it is running in right now).

"Reverse" power: ~ 6,90V +/-5mV, steady.

I hope to have indentical values tomorrow (or less than 1%, now it's about 8,7%), we'll see.

If not, I'll try normal RS-540 motors.

I noticed, slight changes in revs (you can hear that) result in very clear fluctuations in Volts (about 0,10 to 0,30Volts) so this is a very good indication of revs.

Now I only need the relation between Volts and rpm but that's of no importance at this time.

Another thing: input 7,9V (under power), output 6,9V -> efficiency is about 87% (yes, I know this is a very rude calculation...lol!)

All my NiCd batteries have that value, fully charged (the NiMH is about 7,6V though).

Why does a NiCd battery provide 7,8-7,9V instead of the "expected" 7,2V?

 

Dee.

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Another thing: input 7,9V (under power), output 6,9V -> efficiency is about 87% (yes, I know this is a very rude calculation...lol!)

Its not just crude, but plain wrong! LOL [:D]  Efficiency is the ratio of output and input power and power is voltage x current. A stock 540 has as a motor an efficiency of around 60%, when used as a generator much less, propably around 30%, so the real total efficiency of the system would be propably be around 0.6x0.3=0.18=18%.

 

All my NiCd batteries have that value, fully charged (the NiMH is about 7,6V though).

Why does a NiCd battery provide 7,8-7,9V instead of the "expected" 7,2V?

 

As the nominal voltage is the voltage under some significant load (the voltmeter and a free running motor don't pull much current) and after some discharge the voltage measured without that load, especially at a full battery is higher

http://www.rcboataholic.com/images/Battery...rge%20curve.jpg

Cheers 

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Its not just crude, but plain wrong! LOL [:D

Ha ha! Yes, I know! LOL![:P]

It only shows the voltage drop over the test motors (more or less).

This is defenately not a perpetuum mobile as it looses energy by heat and resistance (bearings and internal resistance).

As the nominal voltage is the voltage under some significant load (the voltmeter and a free running motor don't pull much current) and after some discharge the voltage measured without that load, especially at a full battery is higher

http://www.rcboataholic.com/images/Battery...rge%20curve.jpg

Cheers 

Thx again![Y][Y]

Now that I've charged the batteries over night with 1Amp instead of the quick charge (5Amps) yesterday, the voltage is increased to 8,3V (same for the NiMH).

About the link: the color lines in the graphic, what do they mean? Are they different brands, kinds (NiCd vs NiMH etc.) or capacities?

I have understand the NiMhs have a much more flat line (around 7V) between the start and end of the discharge.

LiPos have that too, right?

 

Dee.

PS Any suggestions about the Amps of my test motor as I don't want to blow up my multimeter (it has an unfused 10 Amp circuit/15min max).

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Ok, I managed to get the motors to run equaly.

I adjusted the "reversed ST" about 5 deg. (it runs CW, adjusting is CCW).

I noticed the motor ran pretty hot on the 20 deg. I tried before and gave a staggering 9,72V output, wrong choice and probably a load of Amps!

So, if someone has an estimated Amp rating on my test circuit I can check the Amps with my multimeter.

Btw, I did another test myself to check if the revs are truly equal:

PICT0035.jpg

By judging the sound of both motors running, it looks like they run the same revs.

The sound is "singing", called resonance.

Looks like it worked out ok.

I want to run in both motors with this ESC, would that do any damage to the ESC?

It normally can handle a 15T motor (peak/cont: 200/40A) so with two STs it should work but I need advice on this as electrics are not my specialty.

 

Dee.

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The sound is "singing", called resonance.

Looks like it worked out ok.

I want to run in both motors with this ESC, would that do any damage to the ESC?

It normally can handle a 15T motor (peak/cont: 200/40A) so with two STs it should work but I need advice on this as electrics are not my specialty.

 

Running any mechanical system at resonance would just damage/destroy it very quickly (as amplitude of oscillations and thus acting forces/torques get maximum at resonance frequencies), please don't try to underline your "discoveries" with theoretical background when you don't have it to give them bigger significance (The sound is "singing", called resonance.), it just will make people from those fields fall from their chairs laughing and confuse/give wrong knowledge to others, like if I would try now to analyse a medical problem [:D], as you say electrics are not your speciality, which isn't bad as noone can be specialised in everything, as long as he doens't try to "play doctor" in those other fields. What you hear are luckily only acustic resonances of its casing or other coupled systems (table), but the motor runs overcritical (i.e. over resonance frequency), like also combustion engines, thats why car engines vibrate badly when their RPM drops too low (damaging if done for long time).

The rule of thumb is that a ESC needs half turn limit to power two motors, so 11T for 2xST, but you might get away with it, if your car is light, 2WD and has a short gearing.

Cheers

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What about adjusting fuel powered airplanes with two motors?

I was at a modelshow and asked a lot of questions about fine-tuning the engines to the owner.

To get the rpms exactly the same, the sound should be "singing" or resonating.

It's not the vibrations, it's the sound: big difference!

I know what you mean but that's not the case here.

Maybe you may have misunderstood me, indeed, resonance (as in vibrations) can cause serious damage.

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What about adjusting fuel powered airplanes with two motors?

I was at a modelshow and asked a lot of questions about fine-tuning the engines to the owner.

To get the rpms exactly the same, the sound should be "singing" or resonating.

It's not the vibrations, it's the sound: big difference!

 I agree with you there, sounds like what they do with fullsize planes. The frequencies must line up, any difference will create a "beat frequency". Of course for that to work right both motors must be the same setup, same prop, etc for it to be a true sync. So if the two Sport Tuned motors resonate without any beats (singing) then it sounds like their RPMs are matched.

Or how about this, because I wouldn't be suprised if I was wrong. Back when I was in high school we had an R/C club, and we used a lot of non-mod motors. A Traxxas Stinger (20-turn) was slower than a Sport Tuned (23), and the Sport Tuned motors always ran fine in reverse. Stingers didn't.

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I have to say I agree with you too. [Y]

One thing you should bear in mind is that if you run two motors from one ESC, the power draw will not be the same as just running one more powerful motor.  It's highly unlikely that both comms will spin at *exactly* the same speed and this can cause problems with the ESC if it's monitoring any back-emf from the motor - this is why the twin motor ESCs cost more, and have more circuitry - it's not just a ploy on the makers part to help you loosen more from your wallet!! [ip]

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I have to say I agree with you too. [Y]

One thing you should bear in mind is that if you run two motors from one ESC, the power draw will not be the same as just running one more powerful motor.  It's highly unlikely that both comms will spin at *exactly* the same speed and this can cause problems with the ESC if it's monitoring any back-emf from the motor - this is why the twin motor ESCs cost more, and have more circuitry - it's not just a ploy on the makers part to help you loosen more from your wallet!! [ip]

I can assure you, the motors (are going to be) run at exactly the same revs.

I don't want to get into that now for it will spoil the surprise about the project I'm working on...[;)

 

Dee.

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About the twin engine ESC, how about the E-maxx ESC? (eBay: 130072565690)

Can this be run with one single battery?

What about the TEAM LOSI Twin Motor ESC? (eBay: 280004498209)

Can it handle two STs?

The Traxxas EVX can run on 7.2v just fine, I have done it. It's very easy to set up for one battery. They are rather expensive though, but great for multipurpose uses.

The Losi Mini-LST ESC is designed to run twin 370 motors at 7.2v. I would very much doubt that it would handle twin 540 Sport Tuned motors. It's a good ESC for mini projects though, I used one in my Custom Hilux. Even if you were to use it, the connectors are different (mini-spade for motors and mini standard for batt). The wires are way too small a gauge also. Sorry but that's just not going to work.

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Also should mention, you could probably run any pair of motors on an EVX that you want at 7.2v, I don't think at that voltage there is much of a limit.

Also! Kyosho makes a twin-motor ESC for the Twin Force. It's not as common, but it's a lot like the EVX. It has longer wires though, slightly higher motor capabilities, different programs, and is much more reliable than the EVX. Also the BEC (voltage to servos) is 5.7 volts, the EVX only gives 5 volts. It's a black case with blue sinks; I had one in my E-Maxx and I loved it.

 EDIT: It's the KA-6. Here's a link to rcMart's listing of one for sale. It can also be run on 7.2v and is usually cheaper than the EVX.

http://www.rcmart.com/catalog/product_info...oducts_id=13752

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Also should mention, you could probably run any pair of motors on an EVX that you want at 7.2v, I don't think at that voltage there is much of a limit.

Also! Kyosho makes a twin-motor ESC for the Twin Force. It's not as common, but it's a lot like the EVX. It has longer wires though, slightly higher motor capabilities, different programs, and is much more reliable than the EVX. Also the BEC (voltage to servos) is 5.7 volts, the EVX only gives 5 volts. It's a black case with blue sinks; I had one in my E-Maxx and I loved it.

 EDIT: It's the KA-6. Here's a link to rcMart's listing of one for sale. It can also be run on 7.2v and is usually cheaper than the EVX.

http://www.rcmart.com/catalog/product_info...oducts_id=13752

Thx for the info![Y]

 

Grtz Dee.

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