TOPIC:

Where's Jonny & his topic-tailored picture skills when you need him?

eddrick wrote:

Stick a battery on them, run them up, then reverse the connection & run again - you'll soon hear if it's going faster in one direction than the other.

Yeah, there is a difference... Not huge, nowhere near as noticeable as my Super-stock or Technigold. So the timing is advanced but not as much as these other more sporty motors.

Which leads to the next question - Does it matter?

This is my current stance:-
While this sinario is not ideal, after thinking about it (and discussing it with my bro - he is an electician) it probably is not as bad is it sounds. The motor running forward (advanced) would create a larger magnetic field, draw more current and create more heat(as 'worked' motors do). The reverse running motor would have a much easier life but would still make a fair contribution to moving the vehicle forward.

What do you guys think? I am curious if this would explain Jonny's Clod issues?? Worms, strap-ons or is Taylor Swift better at pulling than pushing???

Yes your bro is correct in what he's saying, but also remember that the effect will be 3x as bad when the motor is actually loaded up & doing work (Remind him about start-up currents vs running currents & why you use star-delta starters with high draw motors). If that work includes driving the rear end faster than its capable of doing on its own, as well,... you see where this is going? In fact, you could argue that you'd be better running a silvercan, than running a tuned motor backwards!

I don't know if anyone else has noticed, but a lot of silvercans run faster in one direction than the other too, & more often than not the faster direction is reverse for the car. The other thing to note is that although timed motors spin faster forward, they make more torque in reverse. More torque less revs is what you need for shifting a big heavy lump.

Yeah sure it'll have a faster top speed with the tuned motors, but you'll probably find the acceleration is less than that of the silvercans (Normally you'd use a smaller pinion with a high rev motor to get around this, but you can't in the clod).

I'd say Jonny's observations are exactly what you should expect - the tuned motor will pull more current regardless. The one running forward will draw more than the one running in reverse, regardless. Add to that, the forward running one will be trying to go faster than the other, ie you're giving it more load than just pulling the truck with a pair of freewheeling wheels, it'll be more like pulling it with a handbrake on (If that makes sense)

I think the general 'rule of thumb' is at a given load an electric motor will draw 6x its operating current during start-up. It is also at this point (0rpm) that it produces its maximum torque and draws the most current. As RPM increases the torque decreases until the load and torque level out. 3x as bad? 3x as bad as what?? I understand more load (such as unbalanced motors) will require more current.

eddrick wrote:

In fact, you could argue that you'd be better running a silvercan, than running a tuned motor backwards!

I am not ready to draw this conclusion yet. If all else was equal I would agree, but they are not. The silvercan produces 237g-cm torque@max efficiency, the sport-tuned produces 350g-cm. from memory the silvercan has an efficiency rating in the 50's, the sport-tuned is well in the 70's. And of course the sport-tuned is capable of spinning faster. As an electric motor's actual operating rpm is determined by load vs torque(amongst other variables) I expect the sport-tuned will be the faster set-up. I suppose my question should be whether the extra power of the sport-tuned is enough to counter-act the inefficiencies created by the different timings (with enough power left over to noticeably increase the performance of the truck!!), and if the extra heat/current draw created by the differing motor timings will be a problem. At this stage I still think it is worth a try.
Surely someone can say "I had some sport-tuned motors in my Bullhead or Clod, and it was {better,worse} than the kit motors!!" I suppose we will find out soon.

-edit- I will catch up with Bro tonight, I will be interested to hear his perspective.

Yep, completely agree with the torque/rpm/current thing, but it's not linear, & how non-linear depends on lots of other things too, especially when it's hooked up to a load with indeterminate variables (Driving style, terrain, mechanical condition, battery condition etc). You have to watch the manufacturer's theoretical ratings, as most are for a motor running on the bench, not real-life numbers. Also remember, the Bullhead isn't exactly the "typical" toy car the Sport-tuned was intended for. (Akin to sticking an F1 lump in a bulldozer)

There was a discussion about this a while back (Can't remember what it was called), complete with posh graphs etc, which was very interesting to see how non-linear tuned motors are.

As for the "3x" statement, most of what I do/test is to do with industrial AC induction motors & "3x the no-load current at startup (Or mechanical overload/locked rotor)" is what I'm used to.
If you tell me it's 6x for toy car motors, I'll take your word for it.

Until someone else educates me, I'm sticking with what I expect to happen - motor running forward is gonna flatten the battery quicker & make it hotter, reverse -running motor is going to be dragged along by the other & make no useful contribution above its own top speed or acceleration.
Anything above the top rpm or acceleration of the reverse-running motor is only going to be done by the faster-spinning, faster-accelerating forward-running motor, hence it will be doing all the work.

As an example, imagine the chassis is a piece of rope, the forward-motor at the front. There will be no point where the rope is ever slack, (If it were, it would mean the reverse motor's going quicker than the forward one)therefore the front is always dragging the rear & the rear plays no part in the forward acceleration. ie it's a hinderance, not a help

Both motors need to be spinning THEMSELVES at the same speed, or they'll be fighting eachother ie one will always be driving the other faster than it's capable of doing itself.

This is the topic about the motor specs :

Click me

I'm quite curious how the motors will behave in practice - compared to a couple of silvercans...

Caught up with Bro last night, he said I pretty much hit the nail on the head with my earlier statement.

vara351 wrote:

The motor running forward (advanced) would create a larger magnetic field, draw more current and create more heat(as 'worked' motors do). The reverse running motor would have a much easier life but would still make a fair contribution to moving the vehicle forward.

He explained it by saying "Imagine a father and a son pushing a car. The father would me doing most of the work and working up more of a sweat, but his job would be made much easier by his son's help."
The 'rope' example presented earlier is not relevant because there is no load present. Picture the same father and son team pulling their car with a rope. The son's help would be much appreciated until the point were the load was so light that the father was able to run along dragging the load and his son along with it. The Bullhead motors will see a significant load as they are moving a heavy truck, and even more load will be created by stop-start driving, running up hills, running through grass, running over my freshly restored Monster Beetle etc. The fact that the father is a faster runner with no load present does not mean he will have to drag his son and the load while they are working together. They will not be working against each other or "fighting" each other. Same as a horse and wagon, you do not have to have two perfectly matched horses.
I don't know why ppl are asking about graphs, motor ratings, etc. The sport-tuned is far superior to the silvercan. If someone wants to see a graph there is one showing this on the Sport-tuned motor's box.
And putting a sport-tuned motor in a Bullhead is like putting a F1 motor in a bulldozer??? This made me giggle as the sport-tuned is a far cry from the F1 of RC car motors, and I cannot imagine an F1 motor making more torque throughout its rev range than a Caterpillar deisel. I see our Bullhead conversion as being more like putting a 350 Chev in a Toyota Landcruiser.

Anyhow, back to my original query about the timing differences, and here is what I expect will happen.
- When fitted with Sport-tuned motors the Bullhead will be more powerful. It will accelerate faster, have more top speed and be able to climb up things easier.
- The Forward spinning motor will run hotter than the reverse spinning motor.
- Run-time may be reduced from that offered by the silvercans, this is a normal side-effect from fitting a more powerful motor to any car.
- The Bullhead will be more powerful with two sport-tuned motors timed differently than it would be if only one sport-tuned motor was fitted.

Of course I may be completely wrong, and we do intend to test our theories in practice. Watch this space.

I agree with most - the father will only have to do extra work when the son can't keep up.
It's not like they are going in opposite directions...

vara351 wrote:

And putting a sport-tuned motor in a Bullhead is like putting a F1 motor in a bulldozer??? This made me giggle as the sport-tuned is a far cry from the F1 of RC car motors, and I cannot imagine an F1 motor making more torque throughout its rev range than a Caterpillar deisel. I see our Bullhead conversion as being more like putting a 350 Chev in a Toyota Landcruiser.

Anyhow, back to my original query about the timing differences, and here is what I expect will happen.
- When fitted with Sport-tuned motors the Bullhead will be more powerful. It will accelerate faster, have more top speed and be able to climb up things easier.

Actually, F chassis and Group Cs are fitted with a Sport Tuned...
The second statement can't hold up - it'll give more top speed but less acceleration and torque than a couple of silvercans.

Replace the father with a breakdown truck, then what happens, at 30mph? Tie the sons hands to the back bumper & how much is he helping?

I am feeling a little disappointed at the direction this thread seems to be taking, I feel it is turning into an argument rather than an intelligent conversation. I have made an open and honest prediction on what I think will happen based on my available resources. As I have already said, I may be wrong and I am happy to admit that if it turns out to be the case.
Does anyone really think the difference in the sport-tuned motors will be similar to that of a little boy compared to a breakdown truck traveling at 30mph? Why post this???
Some common sense is needed when making or interpretting these examples, to refer back to the horse and wagon, one would not team up a clydesdale with a Shetland pony.
In the context of the above post I read the f1/bulldozer statement to be another far-fetched example basically saying we were trying to put a cutting-edge super high revving low-torque motor (something like a 9t) in the truck.

I am curious why Edou predicts the truck will have less torque with the sport-tuned. The sports-tuned produces 350g-cm of torque compared to the silvercan's 237g-cm. The graph on the box shows it well ahead at all times. Am I missing something?