Medusa V2s and MMM/MM - Need some advise!

Hi all,

Current B-Revo:
Tekno Electric Conversion
4s2p A123's
16T clutch bell/pinion, 36T spur
MMM
Mech brakes
Feigao 8XL + RCM Heat sink

Stuff I have on hand, not including the gear in the Revo:
MM ESC + CCBEC
RC-Monster pinions 12T, 13T, 14T, 15T

I was actually looking at the new Medusa V2 range of motors as I wanted to upgrade my 8XL. Was just going to buy a 7XL, but then saw that the Medusa's are rated up to 60k RPM!

My current predicament is this, long story short, I have 2 Kyosho Inferno ST-RRs on the way to me now I'm considering converting 1 to electric as I had already ordered a Kyosho motor mount from Mike, to convert my old Inferno ST.

I've only got 1 MMM, but I have a spare MM with CCBEC that was retired when the MMM came along. The Revo ran fine with a MM+CCBEC with the A123 setup, so I can steal the MMM from that, but then what motor do I use in the ST-RR?

I was considering the Medusa MR-036-050-4800V2-5 as it has more than double the KV of my 8XL, until I noticed it was only 50mm. That's tiny! The 8XL is almost 2cm longer lol.

So then I looked at the Medusa MR-036-060-2000V2-5 which is 60mm, but still only 2000kv. Since it can take higher RPM I guess I can gear it up.

Anyway, so my question is, what do people recommend motor wise for the ST-RR, and also which ESC should I use?

-Use the 8XL from Revo
-50-4800KV Medusa
-60-2000KV Medusa
-Feigao 7XL
-Feigao 6XL

I'd like to stay with the 4s2p batteries as the weight isn't too heavy, and no, I can't afford a Neu motor right at this point :( Damn ST-RRs lol. Maybe after I sell some stuff.

Anyway, any thoughts/advise would be greatly appreciated.
thanks :D

[BL_RV0]

Go with the 2000kv Medusa.

[lincpimp]

I would go with a lower kv motor, and run 7s1p on the MMM. Something like the 1600kv 60mm medusa. High voltage will offset the 1p config, and the lower kv motor will run cooler.

4s2p a123 is just not enough voltage for a heavy vehicle, you current draw will be high, causing heat...

Originally Posted by cdis

Hi all,

Current B-Revo:
Tekno Electric Conversion
4s2p A123's
16T clutch bell/pinion, 36T spur
MMM
Mech brakes
Feigao 8XL + RCM Heat sink

Stuff I have on hand, not including the gear in the Revo:
MM ESC + CCBEC
RC-Monster pinions 12T, 13T, 14T, 15T

I was actually looking at the new Medusa V2 range of motors as I wanted to upgrade my 8XL. Was just going to buy a 7XL, but then saw that the Medusa's are rated up to 60k RPM!

My current predicament is this, long story short, I have 2 Kyosho Inferno ST-RRs on the way to me now I'm considering converting 1 to electric as I had already ordered a Kyosho motor mount from Mike, to convert my old Inferno ST.

I've only got 1 MMM, but I have a spare MM with CCBEC that was retired when the MMM came along. The Revo ran fine with a MM+CCBEC with the A123 setup, so I can steal the MMM from that, but then what motor do I use in the ST-RR?

I was considering the Medusa MR-036-050-4800V2-5 as it has more than double the KV of my 8XL, until I noticed it was only 50mm. That's tiny! The 8XL is almost 2cm longer lol.

So then I looked at the Medusa MR-036-060-2000V2-5 which is 60mm, but still only 2000kv. Since it can take higher RPM I guess I can gear it up.

Anyway, so my question is, what do people recommend motor wise for the ST-RR, and also which ESC should I use?

-Use the 8XL from Revo
-50-4800KV Medusa
-60-2000KV Medusa
-Feigao 7XL
-Feigao 6XL

I'd like to stay with the 4s2p batteries as the weight isn't too heavy, and no, I can't afford a Neu motor right at this point :( Damn ST-RRs lol. Maybe after I sell some stuff.

Anyway, any thoughts/advise would be greatly appreciated.
thanks :D

you dont want to gear up a higher KV motor, you will lose torque when the motor has higher KV and you need that torque when you gear up

[BL_RV0]

Originally Posted by lincpimp

I would go with a lower kv motor, and run 7s1p on the MMM. Something like the 1600kv 60mm medusa. High voltage will offset the 1p config, and the lower kv motor will run cooler.

4s2p a123 is just not enough voltage for a heavy vehicle, you current draw will be high, causing heat...

That sounds like a really good idea, IMO.

Ok what now? I was running 5s1p and 6s1p in the Revo to start off with, and with the 8XL, acceleration was sluggish etc. I posted about it and someone said to try it 2p as the current draw was approaching the edge of the A123's ablitity.

So I tried 2p and the performance was INSANE. 5s2p was really heavy tho, which is why I dropped to 4s2p and geared up. I race the revo and a 5s2p pack on one side made it really unbalanced in the air.

So you're saying, if I were to go to 7s1p A123, that I could use the 1600kv, and I wouldn't have the current draw issues? Speaking weight wise, that's 7cells instead of 8, and any weight saved is great.

I'm a bit lazy tho, and I only have 12 A123 cells. One 7cell pack will not leave me with enough cells to make 2 packs which would make racing rather difficult.

If I were to stay with the current 4s2p setup, would the 60-2000kv handle a truggy? I read a few peeps are using them in their 1/8 buggies with decent performance.
I can just use the 8XL from the Revo, or get a 7XL or something along those lines, if the 60mm Medusa wouldn't hack it.

I could make to 6S packs so I have 2, but I don't really understand how putting more volts into the problem negates the need for more amps lol :D

[Finnster]

Originally Posted by cdis

Ok what now? I was running 5s1p and 6s1p in the Revo to start off with, and with the 8XL, acceleration was sluggish etc. I posted about it and someone said to try it 2p as the current draw was approaching the edge of the A123's ablitity.

So I tried 2p and the performance was INSANE. 5s2p was really heavy tho, which is why I dropped to 4s2p and geared up. I race the revo and a 5s2p pack on one side made it really unbalanced in the air.

So you're saying, if I were to go to 7s1p A123, that I could use the 1600kv, and I wouldn't have the current draw issues? Speaking weight wise, that's 7cells instead of 8, and any weight saved is great.

I'm a bit lazy tho, and I only have 12 A123 cells. One 7cell pack will not leave me with enough cells to make 2 packs which would make racing rather difficult.

If I were to stay with the current 4s2p setup, would the 60-2000kv handle a truggy? I read a few peeps are using them in their 1/8 buggies with decent performance.
I can just use the 8XL from the Revo, or get a 7XL or something along those lines, if the 60mm Medusa wouldn't hack it.

I could make to 6S packs so I have 2, but I don't really understand how putting more volts into the problem negates the need for more amps lol :D

Because power = volts * amps. If power stays even and you up the V, A will drop. You need ~1600W. You can't really go much higher than 70A on the A123s or its too much for the little 2300mah batts. 7 A123s almost gets you there, but I'd almost say 8 on paper, but if people with real world exp w/ 7s1p and say its fine it should be ok.

Thanks Finnster, totally forgot about that formula :D Makes sense now.
I could do 8S a123s easily, as that just needs me to series up the 2 4packs, but I'm pretty sure that's more volts than the MMM can handle :(

Oh, I also forgot the most important reason that I switched to 2p config - runtime.

We run 6min races at my local club, and they're starting to add in 10min mains now, so the 1p config meant I couldn't finish races.
The reason I dropped from 5s2p to 4s2p was weight.

Also, someone just pointed out in another thread, could my uber long motor wires (almost 20cm) have something to do with the higher amp draw with a 1p pack?

And another question; for arguments sake, what would happen in my setup if I changed out the 8XL with say a 6XL (ignore that the Feigaos are only rated to 30k RPM). The 6XL would be higher KV and so in the same setup what would happen? I assume the car would go faster and I assume pull more amps, but what else? Just trying to get my head around what the pros/cons are :D

[BL_RV0]

Originally Posted by cdis

Thanks Finnster, totally forgot about that formula :D Makes sense now.
I could do 8S a123s easily, as that just needs me to series up the 2 4packs, but I'm pretty sure that's more volts than the MMM can handle :(

Oh, I also forgot the most important reason that I switched to 2p config - runtime.

We run 6min races at my local club, and they're starting to add in 10min mains now, so the 1p config meant I couldn't finish races.
The reason I dropped from 5s2p to 4s2p was weight.

Also, someone just pointed out in another thread, could my uber long motor wires (almost 20cm) have something to do with the higher amp draw with a 1p pack?

And another question; for arguments sake, what would happen in my setup if I changed out the 8XL with say a 6XL (ignore that the Feigaos are only rated to 30k RPM). The 6XL would be higher KV and so in the same setup what would happen? I assume the car would go faster and I assume pull more amps, but what else? Just trying to get my head around what the pros/cons are :D

Yes, motor wires do cause more resistance, so that would increase amp draw. The 6xl would run much hotter than the 8xl- check out the thread entitled "Alternative Motor" in the brushless section. One of those models perhaps the ~2370kv model would run well on 4s2p. (That's the kv of a 7xl, approximately. If you have to stick with feigao, get a 7xl, and try 5s2p, if the weight is unbearable, consider moving components to the motor side, or adding small weights to help counterbalance some of the battery's weight. I think you should try one of those 3674 motors, for only $46 it's worth a shot.

[Finnster]

Originally Posted by cdis

Thanks Finnster, totally forgot about that formula :D Makes sense now.
I could do 8S a123s easily, as that just needs me to series up the 2 4packs, but I'm pretty sure that's more volts than the MMM can handle :(

Oh, I also forgot the most important reason that I switched to 2p config - runtime.

We run 6min races at my local club, and they're starting to add in 10min mains now, so the 1p config meant I couldn't finish races.
The reason I dropped from 5s2p to 4s2p was weight.

Also, someone just pointed out in another thread, could my uber long motor wires (almost 20cm) have something to do with the higher amp draw with a 1p pack?

And another question; for arguments sake, what would happen in my setup if I changed out the 8XL with say a 6XL (ignore that the Feigaos are only rated to 30k RPM). The 6XL would be higher KV and so in the same setup what would happen? I assume the car would go faster and I assume pull more amps, but what else? Just trying to get my head around what the pros/cons are :D

Yes, pull more amps and heat up pretty bad. Its better to make power w/ volts rather than amps. In your 8XL setup you are pulling ~120A. You have to have a 2p config. 6XL would pull maybe 140-150 i would guess. It may stress the 2p a bit even if you drive it hard. It may be fine depending how you drive, or you may thermal in mins. Really depends.
I have doubts you can make 10 mins on 7 cells tho. In my Revo I was pulling 1600mah out of a 10 cell pack during a 10 min race. I wasn't driving really hard either. If you scaled the motor to the voltage, I can see 8 cells being enough total energy, but 7 would be close. There are certain holes in configs a123s just don't cover well. You may just have to bite the bullet and get lipos rather than buying tons of motors to try to get the a123s to work.