Brushless 1/8 Buggy

[Batfish]

Hello All,

I'm new to this forum and not quite new to RC; only a couple years in the hobby-grade vehicles, though.

I plan to have a 1/8 scale brushless buggy ready in the next couple months, and would like any feedback and/or advice.

The plan is to put together an electric that can compete with nitro at my LHS. As usual, run time will be the big factor, but I'm hoping I can do well with the new lipo that FMA is coming out with (Scorpion). I would expect the weight savings and efficiency of two 3200 7.4v packs will get me around 15 minutes, or cut it very close.

I plan to start with the Ofna 1/8 Hyper 7 TQ Sport Kit, add in a 9L or 10L, UBEC, and use the MGM 120. I've also got to decide on the right servo. Considering a couple of these items aren't available yet, I've got a couple months to put this together. I've got plenty of 6-cell GP 3300 packs to get going even if I don't have the lipos ready, so I'm really just waiting on the controller.

Any thoughts/advice?

[RC-Monster Mike]

The 10L is probably the better motor choice for this application. The higher voltage is usually more efficient and draws less amps, so a longer runtime results. FMA carries the Kokam Lipos (3200, 20c discharge rate), as does Tower Hobbies, so these are available already. Try to find a plastic or delrin spur gear as well for better pinion life.

Welcome to the Forums!

[Batfish]

Thanks for the reply, Mike.

I figured the 10L was appropriate, but I haven't put a brushless system together yet (just Novak 5800 systems so far) so I'm relying more on advice.

I've visited this forum quite a few times over the past couple months and I wanted to let you know that the way you participate in your forums and provide service to your customers has convinced me that I'll be purchasing my motor and speed control from you. I'll be watching for the MGM 120 to become available, and I'll even pick up the gears from you if you sell them. I'll message you as well.

Based on what I've read here (and elsewhere) it sounds like the MGM 120 would be ideal for what I'm doing, since it promises to be relatively inexpensive and still perform well. Are there any other controllers I should consider? 9918? Schulze? Others?

Lastly, I was aware that the Kokam 20C packs are already available; I was specific with the scorpion comment because of the advertized increase in safety and quick-charge ability. According to RCDriver's review and FMA's website, the battery with their charger is capable of a 20min 90% capacity charge. The batteries are also supposed to have on-board circuitry to balance charge rates and cutoff at the right voltage during discharge.
As far as I have been able to see, the current Kokam packs do not have these capabilities/features.

Thanks again.

[RC-Monster Mike]

Thanks for the LiPo information. the new generation sounds like they have addressed some of the shortcomings of the batteries (I particularly like the charge rate capability and charge/discharge cutoffs). The 9918 is a popular choice for these conversions. It is a very durable controller. the MGM should be quite the performer as well. I will try to reach MGM this week and find any information I can about the new controllers (new expert car controllers will be computer programmable as well!). schulze makes excellent controllers as well, but they don't have the support of the others it seems(problems always blamed on the customer).

[gixxer]

according to there site the scorpion packs and charger should be available in mid may.
https://www.fmadirect.com/site/wolf/scorpionSplashPage/

[starscream]

Kokam does have 20C high rate discharge packs available now but they do not have the voltage cut-off or charging benefits. The only thing I would question is using multiple FMA Lipo packs in a high voltage vehicle. The voltage cuttoff is controllered by the computer on the Lipo pack itself which connects to your controller. So if you are running more than one pack you won't be able to connect more that onne pack to teh controller.
I have a brushless Revo and a brushless 1/8 Mugen buggy and both motors/controllers run with 20 cells. In my case, I would need atleast a 22v Lipo pack. I emailed FMA and they said that they are working on a 6s Lipo pack and charger, for airplanes, that has the same charging benefits of the Scorpions. These will hopefully be available in May or June. The problem is, I don't think a 6s pack would fit on 1/8th buggy chassis.

As far as gearing goes on teh buggy, if your going to make a mistake make sure you gear the buggy too low NOT high. I fried my controller the first day I ran my Mugen. I was using a 46t spur and a 13t pinion. I ran the buggy for 10-12 minutes and the temp of the controller was over 210F and the motor was over 180F :(
I am fabricating new center diff mounts and will use a 62t spur/slipper from an ofna Dominator.

I am currently using GP2200's. They are significantly lighter than the 3300/3700's and have plenty of punch. I get over 12 minute run times which is just enough for those 12 minute mains.

Have fun with your conversion and take it to those nitros ;)

[Batfish]

Originally posted by starscream
Kokam does have 20C high rate discharge packs available now but they do not have the voltage cut-off or charging benefits. The only thing I would question is using multiple FMA Lipo packs in a high voltage vehicle. The voltage cuttoff is controllered by the computer on the Lipo pack itself which connects to your controller. So if you are running more than one pack you won't be able to connect more that onne pack to teh controller.
I have a brushless Revo and a brushless 1/8 Mugen buggy and both motors/controllers run with 20 cells. In my case, I would need atleast a 22v Lipo pack. I emailed FMA and they said that they are working on a 6s Lipo pack and charger, for airplanes, that has the same charging benefits of the Scorpions. These will hopefully be available in May or June. The problem is, I don't think a 6s pack would fit on 1/8th buggy chassis.

As far as gearing goes on teh buggy, if your going to make a mistake make sure you gear the buggy too low NOT high. I fried my controller the first day I ran my Mugen. I was using a 46t spur and a 13t pinion. I ran the buggy for 10-12 minutes and the temp of the controller was over 210F and the motor was over 180F :(
I am fabricating new center diff mounts and will use a 62t spur/slipper from an ofna Dominator.

I am currently using GP2200's. They are significantly lighter than the 3300/3700's and have plenty of punch. I get over 12 minute run times which is just enough for those 12 minute mains.

Have fun with your conversion and take it to those nitros ;)

Thanks for the reply and information, starscream. I hadn't really thought about what would happen with two "smart" batteries hooked up to one speed control. I assume that if one reaches cutoff voltage first it will just cut the power to the vehicle in half, then the second battery would carry the load until it cut off due to it's own circuitry.

I have a couple questions regarding your reply;
I was under the impression, from reading here and elsewhere, that I would be able to compete with 14-18 volts and not have to push over that just to be competitive. I'm sure I'll want to do a couple speed runs, but I just want to be able to run high 20sMPH to be competitive with the nitros. Will I not reach those speeds on 12-14 NiMH or 4 lipo cells?

You mention GP2200 - where do you find them, and what is the average cost? If they are sub-c cells, I didn't expect a substantial weight decrease. I'm interested in hearing/learning more.

Thanks.

[RC-Monster Mike]

High 20's is easy to achieve on 12 cells. There are a few "small" cells that can discharge quite well and may just work in an e-maxx. I haven't tried them, though. 2200 mah would need to have some high voltage to make the runtime (I think they have no more energy per ounce than the larger nimh cells, so net gain would be very little).

[starscream]

I am currently getting my GP2200's from maxamps.com. They are $5.49 a cell. You loose run time but reduce your weight.

The cell/voltage question is a little tricky. There are several factors involved regarding the differences of motor size and voltage. I run a maxcim N32 which runs around 2500 kv at 18 cells. But, like I said, I run 20 ;) I believe the can, of the motor, would be considered an L size.
Its kv = 2500
Voltage = 24
So my RPM per volt is 60,000

I have found that these figures have worked well for racing but I know there are faster motors out there with higher kv but you must also consider the size of you vehicle and your desired run time.

I'm sure you can setup a 12-14 cell buggy that will compete against the nitros I'm just not sure you will get the run time needed.

I would be interested to find out what other people with 12-14 cell setups are getting for run times.

Just for comparison, I get a minimum 20 minute run time with 18-20 GP3300 cells on my maxcim N32 setup.

[RC-Monster Mike]

your rpm per volt is 2500. The total rpms would potentially be 60000 (not likely under load, though). That is an impressive runtime with 3300 cells.

[starscream]

Oops, my bad
Total RPM was 60000 :)
In my opninion, the 2200's are awesome. They are 4/5 SC cells and put out up to 30A discharge.
Check em out at the gp site:
http://www.gpbatteries.com.hk/pic/220SCHR_DS.pdf
You can see the other gp cells here:
http://www.gpbatteries.com.hk/html/t...racing_car.asp

Here's my run down in weight comparison to the 3300's
The 3300's are 2.2oz
The 2200's are 1.41oz
The weight difference between the two at 20 cells = 15.8oz
I save myself 1lb by using the 2200's which is a huge difference in a race.

The 2200's give me around 13-14 minute run times which is fine for 5 minute heats and 12 minute mains.
I have to jump up to the 3300 or 3700's for the longer 15-20+ minute mains.

I am not sure how well the 2200's will work at lower total voltage but at 20 cells they're awesome.

[RC-Monster Mike]

Those small cells would be an excellent way to achieve the efficiency of a high voltage setup without the weight (stress on parts and runtime). It sounds like a winning combination to me.

[Batfish]

The 2200s sound like they would improve performance over 3300s in some situations, yes. I think I'll hold off for now, however, since I've got loads of 3300s and will be jumping on-board with lipo in a couple months.

Great info - thank you!

[starscream]

I posted some pics of my Brushless Mugen

http://www.rc-monster.com/forum/show...=&threadid=441

Later

[Batfish]

I have a new question:
If I'm planning on running on possibly 6 to 8 cells, should I use a different motor? 9L? 8L?
I have read a few posts from someone tracking their 1/8 buggy at 28MPH with a single 6-cell stick pack using a 9918 and 9L geared the same way I'll be gearing. What I'd like to do is run two packs in parallel to increase runtime while being able to run ~30MPH, so I'm figuring 14 or 16 cells, but wired as one 7 or 8 cell pack.
The buggy is listed at 7.7lbs before removing the exhaust pipe and brakes, and adding electronics and batteries. I figure up to 2.2lbs of batteries, plus the weight of the receiver, servo, speed control, and motor. About 11-12lbs RTR?
I just want to make sure I'm getting the right motor for my application.

Again, my goal is to have a brushless 1/8 buggy that can run near 30MPH for ~15 minutes. Ideally, the motor and speed control would be able to handle that twice; back-to-back, so ~30 min at about 30MPH. Right now it looks like the 9918 for sure, just looking for the advice on the right motor.

Thank you.