Brushed motor wiring questions
 

Ok, so I have an "interesting project" and for cost reasons would like to run a pair of brushed motors. Looking at a pair of the kershaw designs 700HO motors and was wondering how to wire them up.

I plan to use a MM and a pair of 2s lipos, wired in series for 4s. Would i wire the motors in series, or parallel?

From what I can gather I want to run them in parallel to get the full 14.8v to each of them. If I run them in series they will only "see" half of the voltage on each motor? This is how I understand it, but please correct me if I am wrong. This truck will not be geared very high, and will have a 2 speed tranny as well. It should weight about 12-14lbs, and have alot of traction! I also would like brushed for the very smooth low speed response, which sensorless just can't seem to match.

You have it right - Series for 7.4 on each or parrallel for both getting 14.8...

Motors are effectively just resistors - in series you will get 1/2 the voltage dropped across each assuming they have the same resistance.

Thanks Chris, I thought I had it right but wanted to make sure. I just found some johnson 550 motors, so I may try them out and see how they do before I drop a bunch of money on the 700 motors. I am cheap sometimes...

If I wired the motors in series they would only go half as fast as they would wired parallel. This may be better as I am going for slow speed with good throttle control. 20mph in 2nd gear is plenty for this project.

Does anyone have any idea what kv the traxxas titan 23 motors are?? I figured they are around 1500kv, but not sure.

Or would it be better to wire them in parallel and just vary the input voltage? I will be using a pair of 2s packs, and can wire them in series or parallel.

You might give it a little while and try the Traxxas 750 motors in the Summit. They should be considerably cheaper than the stuff Kershaw sells and I think they will bolt up to a stock motor plate.

The Titans I believe are 1450-1500 IIRC.

Tower has an ofna 775 motor 10 bucks cheaper than kershaw.

http://www3.towerhobbies.com/cgi-bin...?&I=LXVCL4&P=7

Is it a removable pinion? And its meant for a starter, will it hold up after it gets hot?

They might have a 25mm bolt pattern, but I think they have the 30mm pattern. Remember that the rear facing mount on the revo has both 25mm and 30mm bolt patterns. Plus most 700 motors use the 30mm pattern and also use m4 thread screws. I am sure that they are heavy buggers.

I will try the johnson motors I have. I will wire them in series first and run them on 4s lipo.

I believe the 700 series motors have a 30mm mounting pattern, hence the special mount that Kershaw sells for his 700HOs. You can modify the stock mount, or just buy the mount from kershaw, or even make your own easily enough. As for motor options:

http://banebots.com/pc/MOTOR-BRUSH/M2-RS775-144

1205kv, ideal for slower speeds if ran on 4s lipo.

best brushed motors. I have had the 18 volt dewalt for a while. It spikes at 1900 watts on 6s2p a123 cells. They are also long lived at those high voltages and the brushes are removeable. I even ran my 18 volt motor on 8s a123.:yes: very powerful (brushed) motors.

Any chance you could link me to one of those Dewalt motors?

Thanks for the link Neil. I may just buy two of those...

Ok, time for another question about sereis and parallel wiring...

Would it be better to wire my batts in series for 4s, and then parallel the motors for lower rpm, or wire the batts in parallel for 2s and wire the motors in series? The only thing I can think is that the current draw thru the esc will be higher on 2s than 4s. I plan to use a MM with a ccbec.

Will either wiring method produce any more power or torque? I guess that I will just have to experiment both ways. The motors that Neil linked to look great, and their kv on 4s with my proposed gearing would be almost perfect.

Should work the same both ways and pull the same amps both ways. Either way the motor sees 7.4v and pulls the amps it needs. I think at this point I would wire it which ever way is easiest for you.

I'd suggest paralleling the motors, and running 4S. Unlike brushless motors, with half the voltage going to the motors in series, you'll also get considerably less torque as they can't just pull all the current in the world to make up for the low voltage (like BL); I learnt a lot about brushed motors way back when I was running brushed setups in my old Wild Dagger. If you want lower RPMs, I'd just gear down personally. On 4S, you'll be running them at their most efficient too.

The MM should be able to handle them easily in High-Power FWD-only mode, but might have a bit of a hard-time in reversable mode (at a guess). Just my 0.2 :smile:

Thanks for the info. I figured that I would wire them parallel and just run 4s thru the MM. I will be in fwd/rev mode, so hopefully the higher voltage will help the esc survive. Considering I will be gearing for around 10mph in 1st and 15mph in 2nd I do not see the MM having any issues...

Neither do I- if the crappy Evx2 can handle a pair of 700Ho motors just about on 4s lipo, the MM shouldnt have any issues for sure.

I wonder what the difference between the kershaw 700 HO motor and other 700 motors?

<table x:str="" style="border-collapse: collapse; table-layout: fixed; width: 777px; top: 16px; left: 0px; height: 257px;" border="0" cellpadding="0" cellspacing="0"> <col style="width: 75pt;" span="2" width="100"> <col style="width: 74pt;" span="2" width="98"> <col style="width: 56pt;" width="75"> <col style="width: 87pt;" width="116"> <col style="width: 69pt;" width="92"> <col style="width: 72pt;" width="96"> <tbody><tr style="height: 36pt;" height="48"> <td class="xl24" style="width: 75pt;" width="100">Motor</td> <td class="xl24" style="width: 74pt;" width="98">Output @ 16.8V</td> <td class="xl24" style="width: 74pt;" width="98">RPMs @ 16.8V</td> </tr> <tr class="xl25" style="height: 31.5pt;" height="42"> <td class="xl26" style="width: 75pt;" width="100">Traxxas Titan</td> <td class="xl27" style="width: 74pt;" width="98">About 160 watts</td> <td class="xl28" style="width: 74pt;" x:num="25,000" width="98">25,000</td> </tr> <tr style="height: 60pt;" height="80"> <td class="xl29" style="width: 75pt;" width="100">Revolver 700</td> <td class="xl30" style="width: 74pt;" width="98">252 watts</td> <td class="xl31" style="width: 74pt;" x:num="29,400" width="98">29,400</td> </tr> <tr style="height: 60pt;" height="80"> <td class="xl29" style="width: 75pt;" width="100">Revolver 700-HO</td> <td class="xl30" style="width: 74pt;" width="98">363 Watts</td> <td class="xl31" style="width: 74pt;" x:num="27860" width="98">27,860</td> </tr> <tr style="display: none;" height="0"><td style="width: 75pt;" width="100"></td><td style="width: 75pt;" width="100"></td><td style="width: 74pt;" width="98"></td><td style="width: 74pt;" width="98"></td><td style="width: 56pt;" width="75"></td><td style="width: 87pt;" width="116"></td><td style="width: 69pt;" width="92"></td><td style="width: 72pt;" width="96"></td></tr></tbody></table>

Ok, how about the physical difference? The 700 HO must have better qual windings and magnets, as it seems have a similar kv to the reg 700. I guess that explains the cost. For my purposes the 700 motors Neil linked to will be more than enough.

I think the 700HO motors have 5 pole armatures, rather than 3 poles on the normal 700s... I think.

Sorry I meant to link to it.:lol: Don't waste on other big brushed motors, believe me I have tried them all. Not even close to the dewalts. Here http://www.robotcombat.com/products/dewalt_motors.html The motors I have are the "new" 18 volt motor. The speed controller I used is on this site also.

Thanks, do you think that a MM would be able to handle 2 of them? Any idea what speed they turn at a specific voltage?

Maybe I would only need 1 of them? I really can't see a brushed motor doing more than 500 watts...

I can remember several years ago guys were running the 18v dewalt motor single setup on 16.8 volt nimh and getting around 32-33 mph in the e-maxx. I think one would be plenty for your application.

I think the MM would be easily able to take them...

That sounds good. I may have to give one of them a try. The dual 775 motors look good too, but I would have to buy pinions for them, and a motor mount, I could make a single motor mount easily for the 820 motor.

So I have decided to try the titans first. Looks like 13/72 gearing will do the job.

Remember that the mamba max won't have to switch phase with a brushed motors so it should be able to handle 200-300 amps instead of 100(Of course i doubt that Castle would warranty it at those amp even in brushed mode). It's not for nothing that manufacturer have problem doing brushless controller.

I peaked 1900 watts on my eagle tree with that 18 volt dewalt motor in my 1/5 scale e-maxx/baja(waiting on MM). It was doing a constant 700 plus watts. That was using 6s2p a123 cells. I also ran 8s1p1 a123 and peaked at 1700 watts. If those numbers are right those HO motors suck. Like I said I tried them all before going brushless and the dewalts are the most powerful brushed motors of that size. I still run one in my jugg2 on 6s 123cells. I do think the mamba can run it. Just use the high power wiring setup.

In fact there is a few more powerful brushed motor at that size. One of the most fearsome one are astro cobalt motors reaching 85 to 88% efficiency iirc.

http://www.astroflight.com/index.php...products_id=85
http://www.astroflight.com/index.php...products_id=87
http://www.astroflight.com/index.php...roducts_id=126
http://www.astroflight.com/index.php...roducts_id=128

The astro cobalt 90 is said to be able to replace a .90 glow engine on a plane... 1500-1600 watts continuous which is near a neu 1521 but at 2 pound. The good point though is that controller handling brushed motors are more robust...

Those are a bit more powerful, but the dewalts are one tenth the price.

If I spend 140+ on an rc motor it sure as hell won't be brushed.

You got that right!!!

I may have to get a dewalt 820 and run it on 5s lipo with a MMM. See how good it really is...

Anyone know how effecient they are?

You mean aside from the arcing and friction from the brushes? :wink:

I think it has a built in fan... BrianG cryptonite there:lol:

You may be right, but it would be interesting to play with the "best" brushed has to offer, at least for 40 bucks...

BTW, I have the 6x6 maxx rolling now. Check the build thred!

TBH, I'd use a fan if it was built into the motor, kind of like a Pletty. It's the add-on crap I'm dead-set against. Not only does it look retarded and messy, it shouldn't be needed. But if the fan was built-in, I'd see it as a little extra insurance against heat. And I hate heat more than I hate fans.

Yeah, the plett fan is a really nice design. Makes the 1512 motor as capable as a 1515... I would rather not have the fan myself, but it does help alot on brushed motors.

As per that robotwars wiki, about 81% for the old style can

http://www.robowars.org/wikka/DewaltDrivetrain

Thanks, I may have to give it a try then, that rating is not much worse than a feigao!!!

Keep in mind though that efficiency will fall faster if they are run at lower voltage.

What voltage do they run the motors at? 24v?