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Full Option IMA Integrated Motor Axle
Here are a couple of pics of the new back end I have done for the Mardave, which I am calling the IMA.
https://fbcdn-sphotos-h-a.akamaihd.n...55482142_n.jpg The concept is self-explanatory, and the results are very pleasing. The car drives as smooth as silk, and there is no mechanical noise from the lack of gears. The current set up is using a slightly low kv motor (750) which isn't drawing quite enough current as I can complete a race on about 800mAh on a 2-cell. As a result it lacks a bit of punch out of corners but is very comparable with 'normal' cars in straight line speed. The other benefit is that the whole pod weighs just under half that of a standard plastic pod with 540 size motor and axle. I am going to switch out the motor for a slightly bigger one (35mm can) to try to get a little more low end. Once that is proven, I will move on to stage 2 of the concept, which will be a customised rotor unit for the new motor with an integral diff. Judging by the performance of this, it wouldn't surprise me to see all pan cars change to this type of drive before too long. Touring would benefit even more, with biased F/R drives for better cornering, but that would take some customised electronics in the ECSs to achieve. |
IMA v2.0
Now using Aerodrive 3536 motor, 910kV. This is a lot torquier, more powerful, and the fastest solid axle Mardave I've seen. Got second in the A final at this week's club meeting. Now got to make an integrated diff and it will be the complete package. https://fbcdn-sphotos-c-a.akamaihd.n...33101364_n.jpg |
Really interesting idea here, always good to see others tinkering and thinking outside the box!
Good luck with it, James |
Thanks James, I really think this will be commonplace before too long. It's great to drive.
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Do the race regulations allow this though Dave?
Part of the reason I stopped running 'Dave's at the club was that with a car "built to regs" I was totally out paced by the cars built to the club rules then, including your previous car. |
Apart from 'anything goes' rules I doubt this car would satisfy the regs at any club. Certainly wouldn't at ours. My intention here was to see if the concept worked, which it does, so now I want to perfect it. I've missed enough weeks of our championship to not worry too much about not counting for points.
The rules at Gloucester are still 2S/21.5 or 1S/13.5 to count for points. People who want an easy life, and a cheaper car, go for 2S. People racing elsewhere too go for 1S. The racing is still great and I have to say, the most enjoyable I have had since starting at the club. |
I just wanted to add I have been running with this concept car in recent weeks with a 2s supastox and it runs very smoothly and the current configuration is 100% competitive against the top GT12 runners at the club (GERCC - Gloucester).
It is slightly surreal to see it silently gliding around the track! Good stuff Dave. |
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that I doubt! |
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With this layout the one thing that can't be escaped is the high efficiency. It is currently using roughly 3/4 of the energy to complete a race in a time faster than all but the very quickest GT12 cars at our club - compared to the exact same car running a 21.5T 2-pole motor. Properly designed, the suspension will work better as the unsprung weight is halved. These are major advantages and I am not saying my prototype has maximised any of this potential, but the potential is there to be taken and that isn't the case with a conventional geared transmission layout. |
Don't some clubs still run mechanical speed controllers?
If that's the case I expect they will adopt this system in approx April 2213... |
That's right. Then there are the clubs running tethered cars without radio control at all, they won't go for it either.
Personally I don't understand the MSC runners. Once you factor in a servo and the MSC itself, you could buy an ESC. |
Very cool!
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LR - how will we be able to compensate for tyre wear on this set-up, or change gear ratio to suit tighter or more open tracks? It's a clever use of the torque characteristics of a DC motor!
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There is enough torque to spin up the wheels with this particular motor at low speeds, even with a top speed exceeding the rest of the cars on track by a good margin. I've been running the throttle to 80% so I don't have a crazy speed advantage. I think you might get away with setting up for the biggest track in the country and still have more than enough low end punch for the tightest track. That remains to be seen. Otherwise, rather than changing gearing it would be a case of changing stators. Not a major issue with these complete motors selling for under a tenner each.
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I'm curious how you plan to do a diff on this one. Any chance to see an exploded view: all parts layed out in order before assembly?
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https://scontent-b-lhr.xx.fbcdn.net/...57576593_n.jpg |
used to have an rc18b with an outrunner integrated into the centre shaft, also have a small drag rail with that setup, it works very well but you do need a higher rated speed control and good batteries because startup currents are VERY high. both are/were very smooth to drive, but very limited by the gearing, or lack of. not too bad onroad with foams i suppose because you can true your tyres to get suitable gearing. by the way, you want a really smooth mardave, try a keda 450h 3200kv outrunner, really good to drive!!
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Love to see some pics dodgydiy.
But a Keda 3200 on a Mardave? That would be out of control. I doubt many speed controllers that could actually fit in a Mardave could handle those start up currents! |
Great idea!...well done.....cant wait to see how it develops...:thumbsup:
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https://fbcdn-sphotos-b-a.akamaihd.n...83212582_n.jpg
Components for the motor diff unit. -Motor stator -303 stainless steel through shaft and ring carrier -Modified 14-pole rotor -Acetal ball cage -Standard Mardave steel diff ring -6082 aluminium differential hub -Stainless end cap with stub axle -End cap mounting screws I just completed most of the parts. Test fit time. |
so its not going to be something you can buy off the shelf?
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That depends on the success, or otherwise, of the concept.
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What are these motors normally used in; boats, planes, heli's?
I could very well imagine one of these go into a shaft-driven touringcar; just in front of a pair of saddle-packs. |
These motors are used in multi-rotor helicopters and planes. The ability to swing huge propellers without a gearbox is a big benefit. Price is lower, reliability is higher and efficiency is greater. The same benefits can all be realised in wheel driven vehicles.
On top of that, because the magnets are rotating in the open air and are mounted on a huge annular steel heat sink, they don't get as hot, so you can push these motors a lot harder than an 'inrunner' conventional car motor. So a smaller motor will give more power. In a touring car the inline shaft concept would of course work. In my opinion, the real benefits would be realised only without the transmission shaft, with a motor in each bulkhead and no mechanical transmission at all. Then you can use electric overdrive, on-demand oversteer and all the other things that allow the car balance to be constantly fine tuned for the best performance in all situations. And you can put all your gear right where you want in the chassis - dead in the centre. |
It will need to be in the shaft - only one drive motor allowed in Touring Cars!
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Would this concept work in a v 10 I've got sitting here just fancy having a play with it
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Gerbil - yes.
SlowOne - there are far bigger obstacles than the single motor rule. For a start even one of these motors is not of BRCA legal construction in the first place. |
If,say you were running a 6.5T motor in a car,what would be the equivalent in one of these outrunner motors?
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The bulkheads are a bit narrow also, and twin moters with the assorted ESC = getting expensive Unfortunately I don't have a shaftdriven touring car anymore to give it a try. one more question: am I right in thinking you get a stronger effect of the drag brake adjustment without the reduction on your GT12? |
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Mr. Ed, the drive torque increase in this style of motor is also seen in the back EMF and drag braking effect. You don't get a stronger drag feel at the wheels, it feels much the same as a normal set up in that respect.
Believe me, choose the right motor and there would be more than enough torque to light up the tyres on a touring car without any gearing needed. But, you would certainly need the integrated diff as that's really important for the touring car. As you say, making that whole assembly narrow enough, and developing the appropriate drive electronics would be real challenges - but surely a lot of fun too. Quote:
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Leading the way - Maybe
Given that Brushless motors - Lipo Batteries -2.4GHz Tx have only been adopted in recent years, I must applaud the efforts and skilled endeavours of LongRat :thumbsup:
Proof of Concept is original thinking carried into practice where it could be taken up by manufacturers that would drive prices down in volume production. :wub Another gain is no frictional losses via gears - the possibilities are there for IMA GT12 is a low cost class that has a good following and innovation properly developed has a place in RC. It may take time for IMA to be accepted so keep up the good work LongRat and keep us posted :cool: |
Thanks for the encouragement.
There is a problem with the current design of the motor-diff unit, in that there is insufficient support for the rear of the rotating can. I have a couple of things to try to overcome this... I will update the thread once this is done. Here is a picture of the finished unit assembled. http://i43.tinypic.com/2z9bf9h.jpg |
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As I see it the left outdrive will have the RPM of the motor, while the right outdrive can go faster (in a turn to the left) or slower (in a turn to the right). Sofar all good, but driving a straight line will get difficult unless the diff is set tight enough for the right wheel to keep the same RPM. Could be my lack of insight on how the out-runner motor functions. I do much admire your very good finish of those mechanical parts. |
The outer can of the motor turns, which is directly connected to the ball carrier. This is the part that would normally be the spur gear in a conventional set up. So the motor drives the balls, not either of the outdrives. The outdrives are free to rotate separately from each other and from the motor can and ball carrier.
Think of it just like a conventional Mardave or pan car ball diff, but the spur gear is the end bell of an independently spinning motor. I think I might have a solution to my current problem, some components are on order and I will update the thread when they turn up and I have made a couple more parts. Should be interesting... |
Got it, thanks for explaining that.
Looking at it now, I think the high torque comes mainly from the 14-pole design, and not as much from the out-runner principle, right? Would it be more or-less correct ot say that you could go from a reduction of 1:R for a 3-pole motor, to a reduction 14:3R? Do you need a different ESC for these 14-pole motors? You mentioned the AMP ratings, but anything else? Frequency perhaps? |
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