New kid, twin det. questions.

[Badger]

Hi all, I recently got back into r/c after a 19 year break, lol. Started off (this time around!) with a TT01 chassis to which I've attached a Chrysler 300c body, then I picked up an old TL01 which I'm converting to a Land Rover Bowler using a Kamtec shell and modified suspension, nearly finished building an F350 high-lift with a Dodge Ram Quad-cab shell, and now I've picked up a twin-det which leads me to a question......

Motors. I've been reading all the available info on both this and other forums, and there'a one heck of a lot of confusing info out there, not just about motors for twin det / wd, but motors in general. Now, I want my td to go roughly twice the speed of a standard tamiya motored one, but I also want more torque from a standstill.
Speed is easy, I reckon I'll need roughly 28-29,000rpm with the standard gearing, so that'll be a pair of 18 turn 28,000rpm motors then. Easy..... NOT! I know this will lose me torque, but would a pair of 15x2 giving 28772rpm give more torque than 2 std silver can 540's? Why is a 17x2 slower running than a 17, I thought from what I've read that rpm is a function of turns?
I already have a no-limit ESC fitted and I'm in the process of machining up a new ally chassis on my trusty old Bridgeport mill - this will allow fitment of two 5100mAh battery packs parallelled together for runtime.
I'm open to all suggestions regarding motors, but I have to lay down the following ground rules...
1. 7.2v only, I'm not buying another ESC.
2. 540 size motors are preferred.
3. Must have long runtime between brush changes.

I'm looking forward to any input you guys can give me, thanks, as unfortunately there aren't any good shops within easy reach that are interested in anything other than selling standard boxed models.

 

[bpare207]

A lot of the guys on here love the speed gems series of motors and run them in their clods. A 17x2 will be slower than a 17x1 due to the increase in rotating mass obv. What is it your exactly looking to do? Anything other than the stock silver cans will give you a tremendous boost in speed. As far as torque...if you're bashing go with 15-19 turns there's a thread stickied in here where the guy uses something similar to the Traxxas 12turn titan motors but made by someone else, LRP i think. But, gotta remember that the truck only goes so fast as the amount of volts you run through it, so at 7.2V your only going to go so fast with brushed motors.

 

[Badger]

Hi bpare207, and thanks for the quick reply. I've seen posts referring to the traxxas motors you refer to, but I don't really want to go to 550's and/or raise the volts, I'd rather //l the batteries for runtime. I'm intending to use this truck for bashing, but I'm being greedy and I want better runtime, speed and torque! (It doesn't have to pop wheelies from a standing start, but it would be cool if it could, lol)
Ok then, let me rephrase some of my questions:-
1. If a 17x2 is slower than a 17x1, by roughly what percentage does the speed drop (I reckon roughly 20 percent, from some quick calcs), and what percentage does the torque rise?
2. What motor, rule-of-thumb, will give the same torque compared to a standard tamiya 540 silvercan, 17x2? 19x2? 21x2? 23x2?

 

[Badger]

Guess no-one wants to talk then.......?

 

[bpare207]

Lol, this section of the forum is really dead you might wanna try posing your question in the general section cuz it is a motor question that you have

 

[william g]

I think there is 2 parts to why this has gone unanswered.

1 is the Dagger-detonator trucks are not as popular

2 the parameters you've given.

You can't get something for nothing, and if you won't change the ESC that means you can't up the voltage with batteries.

Want more speed and power you want more voltage, and a brushless setup would be low maintenence and efficient on runtime. And most basic BL systems allow 2s and 3s lipo batteries.

 

[Badger]

William G, thanks for that. I had considered going brushless, but the ESC currently fitted is an "unlimited", so I saw utilising that as a way of keeping the costs down on this one for the time being, allowing me to simply change motors. I can now run twin batteries for runtime, so what I really want to know is what motor (say, 17x2 or 19x2 for example) will give a similar torque to a standard tamiya 540?
On the issue of brushless for the future as and when funding allows, can I run 2 motors from one ESC or does each motor need a seperate ESC? If I had to run 2 ESC's, how do I have to wire them to the receiver?
Thanks.

 

[William]

brushless you'd have to run 2 ESC's but the Ez-run are small footprint
You can read this post, it's in the clod section for more info http://www.rcmt.biz/bd/showthread.php?t=13372

As for brushed motors
stock silvercan is a closed enbell 27t motor. To get torque from a modified motor you have to change gearing. Lower number of motor turns means lower pinion teeth.

So if you go from a silvercan to a 19 better figure dropping 2 pinion teeth at least. 17 drop another and so on.

 

[HawnMT]

so what I really want to know is what motor (say, 17x2 or 19x2 for example) will give a similar torque to a standard tamiya 540?

The lower the turn the motor the more torque you lose. So neither the 17T or 19T will give you the torque of the stock 27T motors. However, your really not using all the torque of the stock motors anyway because the stock gearing(I'm assuming you still have the stock 18t pinions) really are too low a gearing so your making more torque than your utilizing.

So in general the 19x2 will be a more torquey motor than the 17x2 but it also depends on other factors like manufacturer and quality of the motor(hand wound vs machine wound), etc. I have cheap Venom 17T motors that run more like good 19T mtoors.

On the issue of brushless for the future as and when funding allows, can I run 2 motors from one ESC or does each motor need a seperate ESC? If I had to run 2 ESC's, how do I have to wire them to the receiver?

To run brushless on a Dagger you'll need 2 seperate brushless systems and run a y-harness to connect both escs to the receiver.




My suggestion on your setup would be to dump the second battery pack idea and run a single 2s lipo battery and 19x2 motors and get a set of steel pinions from Robinson Racing because the stock aluminum ones will wear out in no time. I say dump the second battery because your just adding dead weight since you only want it for runtime. Daggers are great because they are light and fast but if you start weighing them down your taking away one of it's greastest advantages and asking for more parts breakage.

 

[Badger]

Okay, maybe I didn't make myself clear enough.

The logic behind me specifying "x2" motors is as follows - I'm told, and have found limited info on the 'net to back this up, that a 17Tx2 motor (for example) produces more torque than a 17T.
I know that a 17T is higher revving and has more power than a stock 27T, but this is at the expense of low rpm torque for initial acceleration.

What I'm asking is this - what motor, with a x2 or even x3 configuration, will give similar torque to a stock 27T motor? After I know that, I can then decide on slightly altering gear ratios and/or any other mods I wish to make.

HawnMT, Thanks for the tip regarding the steel gears, I had been hoping just to re-grease them every so-many runs. Won't steel gears just cause high wear on the plastic gear they mesh with though?

Unfortunately, I have to stick with brushed motorsfor the time being on cost grounds, and I am sticking with a twin battery setup as I have just spent a considerable time milling out new chassis plates and threading all the crossmembers, assembling the thing with a full set of aluminium alloy suspension arms, hubs, shock towers and long-travel oil-filled shocks and spent quite some time setting up the internal damping plates and oil thickness to get the required handling for the weight.

 

[william g]

there is no similar torque when comparing apples to oranges
Mod motors need a gear change to produce torque, no way around it. Ohm's laws of electricity.

offroad lower winds is better. ie a 17 dbl is better for offroad than a 17 quad

Tamiya gears are junk, wear to easy (soft) causing the plastic gear to wear. If you have been running the Tamiya gear then you should also change the plastic spur because it IS worn. May not be imediatly noticeable but it is.

 

[Badger]

Ok, thanks for that info re. the gears.

 

[hyperstang00]

and CVD's..

 

[Hardcore]

OFNA Evo (please someone verifie this because i got mines so long ago) dogbones will fit into a daggers axels nicely when you remove the rubber O2-rings.

I had to use them...with 4inch shocks the added ride height made them pop out. That and 2 x 550 motors at almost 20volts (fresh charge of 2 x 7 cells in series) means the standard dogbones don't last very long.

The problem i have is with the added weight of the extra battery is my dagger is very fragile. It breaks so easily if i have a small accident. Especially the TG10 wheel axels.

I've used my dagger with very stick Masher 2000 M3 compound tyres with the above power and never had any problems with the gearboxes apart from blowing a rear diff (i landed off a jump onto tarmac and was slightly ont he throttle still)

Still running the standard plastic gears. I know someone used to use them with 2 x Mamba Max 4700kv motors on 3s lipo. The diffs are usually only the downside.

 

[Rib Tickler]

I used these. Think they're the ones your after.
Ofna Rear Dogbones ( used all round ) #OFN17145

 

[bsrboy]

For what it's worth - I ran a EVX-2 / Titan 23T configuration in my truck for quite a while. The truck was WICKED fast and I had no failures.

1. The Tamiya "upgrade" pinions are fine (not sure about the 18 tooth kit one's though). Use 2000wt diff grease in your transmission and everything stays slick - I've noticed ZERO wear.

2. To run twin batteries mount the 2nd one on TOP of the chassis with velcro strips. It should run the same direction as the 'stock' battery (side-to-side). The truck can take the weight. Adjust your shock oil/preload accordingly.

3. With 2 batteries you WILL bottom out your rear transmission (i.e. - hit the ground) unless you put limiters on the shocks.

4. The dog-bones can take it. So can the axles and transmissions.

5. The truck will pop wheelies on command and flip end-over-end if you stab the brakes hard. Don't drive like a jerk. haha

Good luck!