Brushless 1/8 Buggy
 

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?

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!

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.

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).

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

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.

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).

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.

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.

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.

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.

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!

I posted some pics of my Brushless Mugen

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

Later

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.

The Lehner xl1600 with 15/46 gearing on 14 cells in series will put you in the low 30 mph speed range and will run for a long time. i recommend running your batteries in series vs. in parallel, as you will get more benefit from the improved efficiency of the higher voltage. The xl2000 on the same cell count (also in series) with 12/46 gearing would be around the same speed, but would have more throttle control (higher rpms) and would also accomplish your goal. Either of these setups would be the better way to accomplish this vs. a faster motor (that will run hotter and draw more amps to accomplish the same thing) and parallel packs.

All of my battery packs are 6-cell at this point. Could I expect 30ish from 12 cells with the xl1600?
My gearing will be either 15/47 or 16/47, as the spur is 47 and the two pinions I have ordered are 15 and 16, so it's close to what you mention.

I PM'ed you as well, but I just noticed that the Lehner's have 1/8" shafts and I already ordered my 5mm pinions. Should I just stick with the Feigao for now?

15/47 on 12 cells with the xl1600 will put you at around 29mph. The 1/8" shaft and 5mm pinions is a snafu, though! I have 1/8" bore mod1 pinions, but they won't hold up to the hardened spur gear. I may have found a source for the hardened mod1 gears, but I need to do some research tomorrow to see if I can get them in with a 3.17mm bore (1/8"). If you go with the 15/47 gearing and a parallel set-up as you had mentioned, I would go with the 8L motor.

So it looks like I'll start off with the 8L.
Keep in touch regarding the 1/8" mod1 gears and I'll probably get the Lehner as well, funds permitting.
I'll get the order going - thanks a ton for your help and attention!

:)

My pleasure. I am curious and look forward to your results with this setup. Please keep me posted!

Just a little update:

The speed control and motor are at the post office - I'll be picking those up today.
I have started assembling the buggy kit. A word of advice on the OFNA Hyper 7 TQ Sport kit; if you're familiar with assembling kits you're probably better off not picking up the instructions. The instructions are pretty horrible overall. I think OFNA needs to re-write instructions for a kit assembly...these instructions read like most RTR manuals that just tell you what part goes where in case you ever need to replace something. It's going together pretty easy, however, and I plan on having it built in the next couple days.
If I'm lucky I'll get to take it on it's first run this weekend. :)

I'll be taking photos of my progress and will also do a full write up of my project and experiences with it.

Cool. I am looking forward to the buildup pictures and results.

I got it running last night, albeit only for a couple minutes.

Here's the setup, then I have a question or two:

OFNA Hyper 7 TQ Sport kit
Feigao 8L motor (currently using a 15-tooth mod1 pinion and 47-tooth spur (I also have a 16-tooth pinion))
BK Warrior 9918 speed control (4mm gold connectors to the motor, Deans connector to the battery - soon to be replaced with PowerPoles)
Blue Bird 620MG steering servo (Torque: 126 oz.in, Speed: 0.15 sec./60° at 4.8V)
Hitec HFS-03MM 3-channel FM receiver
Airtronics M8 radio

I tested and ran it on one 6-cell unmatched GP3300 stick pack.

Lastly, my normal digital house scale (which measures only by half-pound increments) says the RTR setup with 6 cells weighs about 8 pounds. I'm pretty pleased with that, even though I know the scale may be off by a pound or so.

I didn't give it much more than 3/4 throttle because I didn't have everything secured yet. Even still, it was pretty quick and I'd say that even at 3/4 throttle it looks about as quick as my stock E-Maxx on 12 GP3300 cells in first gear. Unfortunately, I hit a little bump in my back yard and my servo wire got sucked through the pinion gear. It still works, but looks like an accordion now :) I'll probably end up splicing it if it shows any signs of trouble.

My question: I noticed a fair bit of cogging through the first 1/4 of the throttle, but it took off nice and smooth once I got through that "cogging range". Will the UBEC (Mike, do you have any yet?) help solve this, or is it something I should expect to live with? I did not try a receiver pack, but I'm pretty sure I do have the 4 dry cell box I got with a previous radio that I can try.

Second question: How many cells and/or how much voltage should I be able to safely put through this system? From the stats I've seen, I expect 14/15 cells or 18ish volts to be the top - correct me if I'm wrong. I'm just looking ahead for the inevitable urge to do speed runs :)

I expect to secure the components tonight and get a little movie recorded to demonstrate the "cogging range" I mentioned. I'll post a link tonight if I'm able to get it done.

If you only ran one 6 cell pack, the cogging is inevitable with the warrior. It will be minimized when you attach the other pack in parallel or add a receiver pack. On one pack, the voltage drop of the batteries causes problems for th controllers BEC. The 8L is good for 12 or 13 cells for everyday running, and could be pushed further (more cells) for the occasional high speed jaunt. I don't think the UBEC will help in this case (if the battery drops below 5.5 volts, the UBEC will go into bypass mode, resulting in the same issue), but I do have them back in stock. adding the second pack in parallel or a receiver pack will make a big difference, though.
I am definately looking forward to the video!

Video
 

The video for Phase 1 is up at rcpics.net.
http://www.rcpics.net/view_single.php?medid=54649

edit - forgot to mention that it's 11+MB, just so you know

I put in some titles so you know what you're looking at.

Let me know if you have any questions.

If it looks like everything is held in with zip ties, it's because everything IS held in with zip ties :)

Provided my connectors actually show up via UPS tomorrow, as they are supposed to, I'll have two 6-cell packs wired parallel to test out tomorrow night.
Also, provided it's running well enough and I have the body ready, I'll be trying it out at my local indoor track (www.rcexcitement.com) on Wednesday night. I may be able to get video of it at the track and will post it if I do.

It's great so far and I still have my photos and write-up to do for the current progress.

Also...
Mike, you mentioned that cogging is inevitable with the Warrior at 6 cells...what about 7 cells? 8? I have the equipment to do all 3, and expect to do all 3.
What about the MGM 120 - cogging on 6 cells with that one? 7? 8?

Thank you.

The warrior really only has the problem when the voltage drops below 5.5 volts, so if you run the packs in parallel, the problem will go away. The MGM controllers (and soon, the new BK controllers) have a lower BEC cutoff voltage, so the problem isn't there. On 8 cells, the problem pretty much disappears on the warrior, unless the batteries are real bad.

If you have got a problem with the weight/size of the 8-10 pack, you could also use the new GP2200 cells!

I don't have a problem with weight/size yet, but I haven't found a permanent mounting for the cells yet, either.

I was able to bring it to my local shop and "wow" a couple of people, including one who runs monster trucks all the time and has been thinking about going brushless in his TXT (Mike, I may be sending him your way if he's serious).

I continue to use my crappy 3000 cells while I work on a permanent mounting for good cells. I don't want to rip apart any GP3300 packs because some velcro let go, heh. :)

The 1/8th scale is a little too big for the new track layout at my shop, but it was a little it of fun running it there anyway and having people ask "They let you run nitro indoors?". Guess they didn't bother to listen to it first, heh.

The only problems I had were mechanical with the buggy: a battery pack popped out and ripped a connector off, and a couple screws loosened up (just needed to be re-tightened). The crappy cells got hotter and stayed hotter than either the motor or controller. Speaking of which, should my motor be hotter than the controller with this setup? Neither is actually "hot", but the motor definitely has the higher temp. I didn't measure it since I know it was nowhere near any danger zone - I'm just curious.

On a couple runs in the parking lot, I was able to get to top speed with the 6-cell x 2 parallel configuration. I'd say the top speed there was about 20ish with the crappy cells. I then switched, on the same cells, to 12 series and figure I was closer to 30, but I don't think there was enough room to get to top speed. I expect both speeds to increase dramatically with good cells.

Mike - I still notice very weak braking power, as I had mentioned in my email, even after re-programming. Any thoughts as to what I should check for? I've read posts from people, here and elsewhere, that have very similar setups in E-Maxxes that have to be careful to avoid doing endos, but my buggy stops only about half as fast as letting it coast to a stop on it's own. It took a good 20 feet or more to stop from about 25MPH. I expected it to be better.
EDIT - Mike, I also wanted to mention that running the receiver pack with 4 fresh alkalines AND having the BEC enabled on the 9918 definitely reduced the cogging on 6 crappy cells...definitely.

No video tonight, but I had fun :)

Next steps:
1 - find a stable mounting system for the batteries
2 - I have a small digital thermometer with a sensor lead that I plan on mounting on the speed control and putting the display where I can see it from the outside of the body. I also have a small CPU fan that I'll add to the 3rd channel of the receiver and mount somewhere.
3 - I also want to add an ON/OFF switch to the setup. Any suggestions on what to use that can handle the load and not hurt the system? My personal preference has been to install batteries, put the body on, turn the R/C on, and go. I never liked a system that's on as soon as the battery is connected.

Your braking power may also be lower with bad cells, because the controller uses the batteries as a resistor to brake (the higher the internal resistance of the cell, the lower the braking power)

Maybe this will help you mounting your batteries tight? I'm sure Mike can get them as well.

The powerswitch you'r planning on using needs to be in the receiver path, don't put a switch in the powerpath (batteries/controller) this can hurt your controller.

I hadn't really thought about the batteries for braking. Next run will be with GP3300s to test that out. If it dries up at my house today, I'll try it tonight. Thanks for the information, Serum.

I already purchased
http://www2.towerhobbies.com/cgi-bin...?&I=LX2778&P=7
but I'm finding that it's tougher to figure out mounting since I don't really have a flat surface to put any hardware on. I think my best bet is going to be cutting slots in the rock guards (plastic) and using velcro strips down the length of the packs. I'd like to try the Gorilla straps, but I don't think I can drill into the aluminum on both ends for the mounting hardware and still have room to fit the packs. Lastly, I'll be using stick packs in both 6 and 8-cell sizes, so I need an adaptable solution.

I figured the power switch would reside in the lead from the controller to the receiver - thanks for confirming. All of the switches I've found at RadioShack are 1A to 3A on 120V; will this work? I don't know enough about the current going through those wires. Also, would it be best to splice into the red or the black wire, or does it not matter as long as I interrupt the circuit?

Those holders you've chosen is the better choice! (no doubt)

Thanks for that link!

Do you have a brake exponential on your radio? If you maximize this etting, you should get better brakes as well. Godd batteries should help a bit, too. Serum also gave good advise on the switch. Mount the switch to the receiver leads, not the batteries. You would need a parallel y adapter to mount the receiver pack and controller on the same switch (just plug the controller lead and receiver pack lead to the switch and plug the switch into the channel 2 of the receiver. then, when you turn on the switch, the receiver has power. I can put a y adapter in your package if you would like.

I've got the M8 so yes, I've got just about any adjustment you'd want. I'll take a better look at that, as well. The default brakes have been fine on my touring sedan, stadium truck, E-Maxx, and 1/12th scale, so I hadn't thought about changing them for the buggy. Another thing to check :)

Regarding the y-harness, I'm more of a visual guy and your description doesn't really end up making sense to me. I'm going to attach a drawing I just did at my desk here, and one of a y-harness in the next post. I labelled everything, so if you could help with what goes where (i.e. A1 goes to B2, etc...) I'd greatly appreciate it. If it works out, you could even use my crude drawings as a how-to somewhere else in the forum/site.

Thanks again.

Y-Harness.

Note that wire 1 is red, 2 is black, 3 is orange. I don't remember if I got them in the right order, but it's the color that's important, so I hope it's good enough to work with.

It is much easier than you diagram makes it out to be. There is a thing called a y harness. All it is a receptacle for two servo leads on one end, with a servo plug on th other. You plug both items that you want to run from the same channel in the receptacle, and plug the servo plug into the receiver. In your case, you would plug the esc and receiver pack into the receptacle, and plug the servo lead of the y harness into the switch and plug the switch into the channel two section of the receiver.

Yep - I'm familiar with a y-harness...that's what the second diagram is ;)

I guess my confusion is from two things;

1 - Can you plug both the ESC and the receiver pack into CH2 on the receiver? I always assumed that the receiver pack HAD to be in the slot specifically designated for it on the receiver.

2 - I have a switch that came with a previous radio, and I tried to put it in-line with the ESC early on. Steering didn't work, only the throttle worked, and I assumed it was because the switch only has the red and black wires, and no third wire. I guess I'm looking for a switch now that has all three wires.

All that in mind, I think what you're telling me (based on my drawings) is that I need to plug my receiver pack into "B" on the harness, and my ESC into "C" on the harness. Then plug "A" into an on/off switch and plug the other end of the switch into CH2 on my receiver. Is this right?

I'm sure what you said in the last reply is right - I'm making it more difficult than it needs to be :)
I just want to get it right. If I'm going to show those nitro 1/8th scales a competitive electric, I should at least have working electronics :)

"All that in mind, I think what you're telling me (based on my drawings) is that I need to plug my receiver pack into "B" on the harness, and my ESC into "C" on the harness. Then plug "A" into an on/off switch and plug the other end of the switch into CH2 on my receiver. Is this right?"

Yes. You do understand. You will need a switch harness with three wires(most times, there is a receiver pack OR BEC, (not both), which makes your setup a little different. The receiver pack can be plugged into any channel in the receiver. In fact, sometimes the servos work better when the receiver pack is plugged into another channel (not "bat" slot), as some receivers limit output voltage to 4.8 volts when using the "bat" slot.

Just figured I'd mention that it's been wet here for a couple days, and it probably won't dry out 'til tomorrow afternoon. I'm hoping to get more done in the way of testing tomorrow.

Mike - here's a picture of the motor clamp/heatsink mounted. By the way, it takes a fair bit of effort to take a decent picture of it using a flash since it's so shiny. :)