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Old 08-20-2008, 03:25 PM   #106
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Wonder how this would work in a 1/12th with the Speed Passion GT Comp speedo? I need a new, 4 cell capable ESC anyway, and dont want to use a Novak.
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Old 08-20-2008, 03:55 PM   #107
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Some of the new speedo's are already coming with a 3 volt cutoff option dor single cell. The Tekin's have a 3 volt cutoff and are smaller than the SP speedo.
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Old 08-20-2008, 05:42 PM   #108
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I guess the picture of a DC-DC 5V steup converter didn't spark any interest.

I have a castle BEC 10A peak and the device is smaller than a AMB personal transponder. 3A is suitible for more aplications, and 1.5A with capacitor is suitible for 1/12 and below. Adding the capacitor to the circut is nominal since most already have one installed on the RX in the form of a glitch buster.

The problem with todays ESC BEC's is that they are voltage regulators not voltage converters. Regulators can only step down voltage. If cost wasn't a big deal, I would love to see a programable 20W DC-DC convertor on ESC's. If I wanted 6V for faster servo transist or more power, I could have it. If I wanted to dial back the voltage and servo speed, I would set it to 4.8V.
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Old 08-20-2008, 06:12 PM   #109
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Oh, the DC-DC stepup converters are VERY interesting. Just not sure it's worth spending $11 a piece and having to parrallel several of them. Not to mention shipping time/cost from Australia.

I was looking at the SP speedos for a few reasons. They're less expensive than the Tekin ESCs, as they come with a handheld programmer vs having to buy Tekins Hotwire program. Also, Tekin RS Pros aren't available yet. Still, I might have to consider a Tekin if it's smaller/lighter than the SP. How do Tekin Redline 13.5 motors compare to SP's 13.5 motors?
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Old 08-20-2008, 09:12 PM   #110
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Quote:
Originally Posted by Bigshades View Post
My LHS doesnt have minimum weight req's, but again i'm not trying to race equivelant at the moment. When i can get things working the way i like, i'll work on making equivelancies.

Unfortunatly, my Sidewinder ESC doesnt allow me to program a cuttoff at 3v, because it will not function at 3 volts!!! So i cant use this particular ESC. I have tried a G11 ESC though, and it apears to function at 3v (no cuttoff though).

I have come up with a good idea for eliminating complex electronics, or an entire RX pack. The lovely thing about batteries is that you can put them in series, and increase voltage. Did anyone ever think of mixing lipo and Nimh Together? Look at the attached diagram.

I can leave 6 lipo's in parrallel, have them hooked up to the ESC. Then i can add the single Nimh cell (400 mah) in series with the lipo's, creating a 4.8v source for the reciever and servo.

I am going to use a 400mah nimh I found laying around, its pretty small, and i can easily mount it somewhere. Now my electronics will function, and i only added a single cell, rather than an entire RX pack.

I have ordered the rest of the lipo's i will need to build the pack. I am very excited to see how this goes.

But being in series, you increase voltage, but the capacity stays the same. So when the 400 mAh cell has given its power, that cell will go to 0 volts, correct? It's been a while since I had classes on circuits, but I think this is correct...
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Old 08-20-2008, 10:30 PM   #111
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Oh, the DC-DC stepup converters are VERY interesting. Just not sure it's worth spending $11 a piece and having to parrallel several of them. Not to mention shipping time/cost from Australia.

I was looking at the SP speedos for a few reasons. They're less expensive than the Tekin ESCs, as they come with a handheld programmer vs having to buy Tekins Hotwire program. Also, Tekin RS Pros aren't available yet. Still, I might have to consider a Tekin if it's smaller/lighter than the SP. How do Tekin Redline 13.5 motors compare to SP's 13.5 motors?
The RS and RS Pro are available. I've seen them in person, just that Tekin is still trying to catch up with demand. I don't know how the RS will handle Hot MOD motors but my instinct says that it should be able to go to 4.5 or 3.5 because of the weight of a 1:12 and the fact the throttle may be closer to 100% when driving.

Shipping from AU is only 14 day at most, and honestly, I don't mind cutting out the middleman once in a while when I need a very custom part.
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Old 08-21-2008, 07:07 AM   #112
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Not to derail the thread completely but... The RS is probably not going to run compeditively in 4 cell with anything lower than a 5.5 turn. The speedo needs to have some cooling air in mod and 12th doesn't provide much air flow for the speedo.

The good news is that with single cell LiPo, everything should run cooler. When I ran single cell in 12th you could run a 3.5 turn/Novak GTB without any heat issues. It was easier on the electronics and easier on the tires (running at legal weight).

My car didn't work when I tried running below legal weight because it forced too much weight to the front of the car.

Last edited by Fred_B; 08-21-2008 at 08:09 AM.
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Old 08-21-2008, 09:08 AM   #113
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But being in series, you increase voltage, but the capacity stays the same. So when the 400 mAh cell has given its power, that cell will go to 0 volts, correct? It's been a while since I had classes on circuits, but I think this is correct...
Correct. That voltage (4.8v) will have the capacity of the single cell, whether it be 400 or 1500. The cell's voltage will drop down when it completely discharges, but it will still have 3.6ish volts from the main pack. But my 400mah cell should last me for at least a run. Worst case scenario, i get a larger cell!

John.
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Old 08-21-2008, 03:35 PM   #114
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I was never planning on running 1/12th mod anyway, just a 13.5 to run stock against 4 cell nimh/17.5
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Old 08-23-2008, 01:37 AM   #115
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Default 1 cell LiPo is the way to go . . .

Good news all!

I spent time evaluating several combinations of the following in a Rev 5 and am happy to report my findings . . .I thought about posting my fast and average laps and such with each combination, but the traction was so inconsistant that I didn't feel it would provide meaningful data. I was able to drive each combination enough to get a solid feel for the characterisitcs and test each under 8 minute racing conditions.

Mongoose ESC
4 cell NiMh
1800 mAH 25C 7.4v LiPo
Novak 21.5ss
Novak 17.5ss

First of all, for 12th scale stock, entry level, novice, or anything other than EXPERIENCED drivers, 2 cell lipo is WAY too fast. I ran it with a 21.5 geared like a 17.5 (76/40 READ: undergeared) and it felt like I had a 10.5 in it. Fast enough that I didn't even bother to try the 17.5 with it.

After reading several threads about the potential of LiPo in 12th scale, I initially leaned towards 2 cell because I thought it might simplify things. The weight would be closer, it wouldn't require a receiver pack, and before tonight, I thought a 21.5 would be slow enough for novice/stock classes.

Now I am all on board with the 1 cell idea. We need options that are slow enough for beginning drivers, and I believe it would be a challenge to create the motors to accomplish this. I know the 1 cell BEC/receiver issue will need to be resolved, but this seems less difficult than re-engineering motors.


So on to the results . . .

The 21.5 with a 4 cell NiMh and a GTB was surprisingly competitive with a 17.5 4 cell NiMh.

The Mongoose handled the 21.5 NiMh exactly like the GTB did. It was also 20 grams lighter and the smaller footprint allowed me to center my electronics MUCH better. The cap is also much smaller and the wire exits and orientation on the mongoose provided for a cleaner install than the GTB. Not to mention retail on a mongoose is SIGNIFICANTLY less than a GTB.

I kept the same gearing with all the tests (76/40) and the Mongoose barely warmed at all. Enough that I didn't need to temp it. The 21.5 never came off more than 110with the GTB or the Mongoose, and the 17.5 came off around 140 with the GTB.

I'll be able to test the Mongoose with the 21.5 again under actual race conditions in the coming weeks, as well as trying it with the 17.5. I just thought I would share my preliminary reuslts for any who care.

For right now I think 12th is in good hands with the EP and Ener-G NiMh cells. I am pretty content with it honestly. But if I can find a way to run LiPo efficiently, I'd love to have the option even if just for practice.
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Old 08-23-2008, 10:48 AM   #116
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The 1 cell Lipo option will allow tracks to find a motor that is suited for it. If your club has a very small tight track then using a 17.5 be the way to go. If your track is bigger than you can go with the 13.5 which will be a bit faster than 17.5/4 cell.

I know some don't seem to want to use a reciever pack but I really don't see this as a big deal. Take a 350mAh lipo it will run for atleast half an hour before it needs to be recharged.
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Old 08-23-2008, 02:48 PM   #117
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I don't think that receiver packs are a big deal to use either. NiMh receiver cells are very cheap and pretty much maintenance free. I just keep a seperate charger for my NiMh stuff so I don't have to worry about getting the wrong setting on my charger.

The last NiMh 4 cell pack I got lasted for an entire season of racing but I have 2 year old LiPo packs that I run in sedan that are still very close to what they were new. That's the advantage to LiPo for me and if it takes a $6 NiMh receiver pack to avoid buying one or two $40 NiMh packs a year I'm fine with that.

As a side note, a big thanks goes out to Danny for forcing Intellect to fix their cell issues. I haven't baught any of the EnerG cells yet but I feel a lot better about my cells for Cleveland not blowing up.
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Old 08-23-2008, 05:54 PM   #118
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I just like the fact that with single cell LiPO and lower wind motors I can use my pinions 15 ~ 50 again. I think I have like 150 pinions doing nothing.... Seems all my rollouts are using pinions in th 55~58 tooth range with 13.5 oval.
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Old 08-23-2008, 05:56 PM   #119
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If you can't wait for a single cell lipo to come out, just wire up some 3-cell NiMh packs and use a dummy spacer. Might have to use ballast to balance the car, or just move things around.
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Old 08-24-2008, 09:07 PM   #120
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Hey guys, I've made a 3.6v saddle pack!!!

I was originally planning on using 6 cells, but only had 4 cells. So the pack is 700 x 4, a 2800 mah pack.

Mounting it in a 12L4 was very easy, all I used was mounting tape. There are two wires to hook them up in parrallel, but they can easily be moved/connected to.

I added a 2cell Nimh pack, in series with the lipo, and powered the reciever with it. It mounted under the shock, in between the two lipo saddles.

I Tested the pack with my 12l4, i changed nothing except the battery type. 27t, geared for 4cell Nimh. I noticed right away that It accelerated much faster. Maybe it was the lack of weight, or the low resistance/properties of lipo's. Top speed was slightly reduced, but thats expected with a lower voltage. But pick-up was noticably improved. A larger pinion could be installed to increase top speed, as torque is plentiful.

Handling felt a little different, mainly because of weight. I ran the car with a 4 cell Nimh setup, so it probably isnt fair. I emmediatly noticed that the car liked to spin a little more. Steering was plentiful, and I believe that a harder compound front tire would be benifitial (or less tire sauce). I ran for about 20 laps total, so i didnt get a fantastic feel for it, but I felt that it had some benifits. I turned down the Dual rates, and it was managable.

I cant give absolute justice to this setup yet, but i feel it is for the better!

Here are some attached pictures, just of the lipo mounted in my car, wires and shock out of the way.

John.
Attached Thumbnails
SMC 5700mAh 25C Single Cell Lipo-edited1.jpg   SMC 5700mAh 25C Single Cell Lipo-edited2.jpg   SMC 5700mAh 25C Single Cell Lipo-edited3.jpg   SMC 5700mAh 25C Single Cell Lipo-edited4.jpg   SMC 5700mAh 25C Single Cell Lipo-edited5.jpg  

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