New from Kershaw Designs:

If you're one to keep your ear to the ground for what the next big innovation from the RC industry is, then you'll know that this truck embodies them all. Major manufacturers are scrambling to release large scale vehicles. Brushless motors are just beginning to show up in production RC cars. This truck can be had with all of these features wrapped up into one. And, by the way, try to find a large scale truck with 4WD.

Features:
[ul][*] Your choice of 9 different power systems, custom systems or install your own [*] [link=http://204.186.93.64/Comstock-MST.html]MST (Metal Spine Technology)[/link] chassis for a light weight but stiff rig [*] Differentials built from [link=http://204.186.93.64/Comstock-Diffs.html]extra large 1.5 Mod gears[/link] - 50% larger than the industry standard [*] [link=http://204.186.93.64/Comstock-Gears.html]9mm wide extra large gears[/link] that better distribute the punishment of dual brushless motors [*] [link=http://204.186.93.64/Comstock-Underside.html]Battery tray[/link] that can be turned around 180 degrees to vary battery pack position and weight distribution [*] Choice of [link=http://204.186.93.64/Savage1-6thConversion-Tires.html]7.5" CEN chevron tread tires or 7.5" Bow Tie style tires [/link][*] 7 15/16" long 1/5 scale Redcat aluminum shocks [*] Room for 2 batteries up to 165mm long, 51mm wide and 50mm tall [*] Accepts dual steering servos. Radio system not included[*] Each truck is built one-by-one by hand. If you want any custom parts installed, don't be afraid to ask!
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$999

Link to... [link=http://204.186.93.64/Comstock.htm]Kershaw Designs - Comstock II[/link]

Dan Fischer
KershawDesigns.com

ya, these are verry cool. but they have been out for a while now.

Must clarify something. There was a Comstock that had been around for about 3 years. The first generation Comstock was based on Revo suspension with extended arms. The truck shown, while it maintains the same body and scale, is the second version whose chassis has been redesigned from the ground up.

Dan Fischer
[link=http://kershawdesigns.com]KershawDesigns.com[/link]

how are you planning to combat the fact that two BL motors never spin at the exact same speed even if they are the same wind? this would cause condsiderable strain on the drivetrains and motors/esc's

the lug

got any action videos of it with the dual brushless system?

Well, thus far, the truck has tons of runs on it and, with checking ESC and motor temps with and without motor heatsink/fans, I notice no trouble with one motor reaching any significant temperature over the other. I can make a good educated guess that when using 2 entire brushless systems in an RC truck, using motors and ESCs from the same porduction run of the manufacturers is enough to make sure the systems run in synch.

However, if you have any expereince to the contary, please chime in.

Dan Fischer
[link=http://KershawDesigns.com]KershawDesigns.com[/link]

Not yet, but they are sure to come. Check back here from time to time...

[link=http://204.186.93.64/Videos.htm]Kerhaw Designs Videos[/link]

The issue with two brushless motors running in one vehicle being out of sync is vastly overblown. It may theoretically stretch one motor if another is struggling, but the actual, real life stress this puts on the motors compared to hauling a 14lb rc chassis around with 7 inch rims on it is negligible.

Truck looks great incidentally, must be sickeningly powerful even with 2 crap motors onboard. Those diffs look like they could take on just about anything.

Thanks, and I'll second that motion.

Dan, do you think that you will ever offer gassers in 1/6 scale, or are you all about the electrics?

Just to make sure we are onthe same page, I take it you mean gasoline powered cars as opposed to nitro?

i believe your referring to load sharing.

generally when low volt ac motors are run together (less than 600vac), and the motors are within 125% of each other in terms of hp/watts, its really not required, even when both motors are shafted together.

should be a non issue.

however,,,,,,,,,,,,,i wouldnt mind seeing someone experienced in the rc field confirm this, as my experience is with much larger multi-motor drive systems, like 8-12 200hp ac motors line linked and shafted together. maybe "access" could weigh in, from my reading here he seems pretty sharp on the subject.

i didnt see it but lilred machine is pretty much on the money

it may be negligble but i read somewhere that traxxas had to do something fruggly to get thier V twin emaxx in sync, and Joe Ford of CC strongly recommended against running a dual motor setup, so i was just curious if you had come up with a solution or if you felt it didn't effect it

the lug

hey lug,

i could certainly be wrong, and if traxxas had to do something to rectify a load sharing issue, then it would suggest i am, lol.

but in my work (high speed web printing press (i.e. stop the presses, stop the presses, we got a new headline!!!!!!!!!) its very common to gear up multiple 3 pole ac motors and run the dog out of um' without worry of load sharing issues.

edit: in fact, we have disconnected power to certain motors for standard maintanence of the output controller for that motor, and just let the remaining motors keep on pulling, keeping the down motor spinning while we do our thing without any issues at all.

Efficiency is the key to everything brushless, a few percentage points efficiency can mean the difference between a setup that runs cool and one that runs hot. You're almost always going to be better off with a bigger motor than two smaller ones. Do you remember the traxxas E-maxx twin VXL concept? Not only was this never released to the public (for it's brushless MTs, traxxas ended up going with a OEM castle creations system), but if you look carefully the ESCs were joined together with some kind of communication cable between the two. Presumably to syncronize the otherwise sensorless brushless ESCs and keep them from fighting each other, which would contribute to inefficiency.

With brushed this was never much of a problem since the switching of the motors depends completely on the shaft position. But with brushless, if you have each ESC switching independently, in the best case, you've lost some efficiency, in the worst case you might strip a spur gear or something similar (if you have two motors that tend to fight each other really hard).

There are some applications where multiple motors might make sense, but we haven't seen many of those enter into RC as of yet. Most of these applications call for motors that are not on the same transmission system, but instead each motor drives one or two wheels and then by varying the power or speed of one (or more) motors intelligently, the user has an advantage in control. For instance, a dual MOA (Motor-on-axle) crawler where the motors are run or stopped selectively for a 'dig'. Or even a motor-to-wheel direct drive, which could in theory steer without the need to yaw the wheels in the horizontal plane, but merely by increasing or decreasing the speed of one's side wheels.

And don't think I know everything, there have been times when I've been corrected by others here. But I think most everyone has in the past agreed with the dual vs. single motor concept. It's like how you don't see dual-engine cars in existance... if more power is the end goal, it's easier, cheaper, and poses less problems to just increase the size of the engine.

The above post mentioned an AC motor, and this is a slightly different case since, other than at spin-up and spin-down, the phase and frequency of the AC solely control the position of the rotor. So, even if completely independent (not on the same shaft), two AC motors run from the same AC source (or inverter) should eventually 'sync up' once they reach their top speed (a factor of the AC frequency, provided there is enough current for a given load). Though I could be wrong, AC motors aren't my thing, I've been wrong about stuff before.

neither one of my degrees is in engineering so I won't argue anything other than having built and played with several different dual brushless trucks I can attest you might get 4 hours you might get 40 hours but don't be suprised if it phases once and burns the spur, pinion or even shears off the motor shaft, with the big pop can sized brushless motors we have available there is no reason for 2 motors, let along one 1950 lehner or neu 1527 is probably enough while still being a "small" motor.

Yes, gassers like something with a 26cc or 30cc motor. That would look awesome on one of your chassis.

I gave it some thought, but many large manufacturers (FG, Harm, HPI...) would just make too many vehicles that are much more cost effective. Now giant nitro trucks are another thing.

i think giant gas are way better than giant nitro unless you start looking into .46's and bigger, yes they have been done but they're all converted heli or plane engines and don't really law it down like todays .28's or .21's in regards to displacement/max rpm's so unless they really become popular i don't expet to see many big high output nito's for cars, just cuz of gas more bang for your buck and less hassle,

the lug

Yes, I agree. I used to make a few large scale nitro years ago, but decided against putting the time into the designs. Just not enough interest. For those that are holding out with nitro, I do have a .70 Thunder Tiger engine out of an EK-4 here that is begging to be installed in a large scale chassis.

Dan Fischer
KershawDesigns.com

Hey Dan,

Do you have a photo gallery of some of your older stuff, I would love to see what you have done in the past with the nitros.

1/5 scale buggy with the Thunder Tiger .70 Engine and Savage 2 speed tranny...

Quite frankly, two motors is cooler than one. Nothing like lifting the hood and having two phat cans sat there.

Every truck I've ever seen with 2 motors hasn't really had a problem. Traxxas has to account for every eventuality if they are thinking of releasing a product to the public, hence the sync cable.

If someone builds a custom truck with two BL motors then they are likely to not mind repairing the damage that this setup can do. If you are going to release a truck to joe bloggs on the street, with a warranty then you HAVE to make sure it works under normal conditions without failure. The sync issue isn't huge, but a truck that will randomly sheer spur inputs or motor shafts every now and then isn't something that the average bloke/girl on the street with a fistful of $ will necessarily want to deal with.

Me, Access, Dan, J.D.T etc. won't have an issue. Incidentally I once fitted 2 feigao 9ls in an E-savage. It was insane but the drivetrain was screaming for mercy after around 40 seconds.