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Old 11-14-2009, 02:35 PM   #1
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Default Pros and Cons - Mid motored TC's

Just thinking out loud here, but happy for all views/inputs.

Have a look at this pic, its of a drift chassis (Tech Racing I believe):



Now, I know that with the stick LiPo across the chassis like that, you have a fair amount of weight away from the centre of the car, and the rear belt needs a tensioner to lift it a little. But, how about swapping the stick LiPo to a saddle LiPo? If there is enough room, you could slide the pack halves forwards or back for weight balance, and finish it off with lead?

Its something I've thought about since I ran a Schumacher Axis 2 years ago, and having seen an RC Lab 7.7Pro up close, I think the mid-motored car would be a quick (and yet different) choice?

Its the current vogue in off-road to have rear cells with a mid-motor, but I can't see shaft getting popular again.

Debate/discuss/moan.
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Last edited by academygaz; 11-14-2009 at 04:15 PM.
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Old 11-14-2009, 02:55 PM   #2
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In terms of centralising mass, the old saddle pack designs are better with the lightweight LiPos.

There are 2 issues though...
  1. The high layshaft, Although its impact on CG is minimal, the perception is that a high layshaft car "isn't as fast".
  2. Saddle pack lipos offer less performance from the same total dimensions, and in the long term I am concerned about balancing (four or six cells which cannot be truly individually balanced)

An alternative is a low-layshaft car like the Axis, but that then has the motor (which weighs 2/3rds as much as the LiPo) offset out wide again.

Time to dig out all your vintage tourers. If they were fast with NiCds, they'll be fast with LiPo too!
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Old 11-14-2009, 03:43 PM   #3
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J.Cyrule used a similar chassis for the 2006 worlds.

see pix from OVERRC, best electric rc website EVER ! ( usually the pictures are very good, not blurry )

http://www.overrc.com/courses/course...oshcyrull5.jpg
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Old 11-14-2009, 03:56 PM   #4
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Quote:
Originally Posted by sosidge View Post
  1. Saddle pack lipos offer less performance from the same total dimensions, and in the long term I am concerned about balancing (four or six cells which cannot be truly individually balanced)

An alternative is a low-layshaft car like the Axis, but that then has the motor (which weighs 2/3rds as much as the LiPo) offset out wide again.
How can saddle pack lipos have a problem balancing? They are just two 1s lipo packs wired together. Isn't that the same as a 2s pack? If you have a problem with balancing then split the packs up into single cell packs, and run female by double male harness in the car.
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Old 11-14-2009, 09:20 PM   #5
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[LIST=1][*]The high layshaft, Although its impact on CG is minimal, the perception is that a high layshaft car "isn't as fast".

pls explain why?
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Old 11-15-2009, 03:53 AM   #6
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Quote:
Originally Posted by sosidge View Post
[*]The high layshaft, Although its impact on CG is minimal, the perception is that a high layshaft car "isn't as fast".

An alternative is a low-layshaft car like the Axis, but that then has the motor (which weighs 2/3rds as much as the LiPo) offset out wide again.
I see what you mean but the layshaft doesn't have to be high to have a (nearly) centered motor. On the pic I enclosed the front belt actually goes through the motor mount, like a yok MX4 I think. On the drift car shown, the layshaft is high because of the battery across the chassis, but they could have made it low just by using two tensioners. The very first SST had a transversal battery like that AND a low layshaft, and, they just used two tensioners to route the belt over the battery. What forces someone to put the layshaft higher are one-belt desings such as the xxxs and robitronic cars.

A design i would love to see is a saddle lipo pack mounted in a magic E4 like the first prototype pictures that were shown on rc tech. Rear motor+ 2 saddles transversally, the servo, ESC, RX go on the sides. That's 3 belts but hey, who cares.
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Old 11-15-2009, 09:31 AM   #7
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Quote:
Originally Posted by boybawang View Post
[LIST=1][*]The high layshaft, Although its impact on CG is minimal, the perception is that a high layshaft car "isn't as fast".

pls explain why?
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Old 11-15-2009, 01:34 PM   #8
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It's good for a drift car application hence Tech Racing labeling it a drift car. Other than drifting though, the tried and true layout of almost every car out right now is close to ideal until, 1) lipo batteries change shape or 2)motors change shape.
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Old 11-15-2009, 03:42 PM   #9
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Quote:
Originally Posted by Racing4Evo View Post
It's good for a drift car application hence Tech Racing labeling it a drift car. Other than drifting though, the tried and true layout of almost every car out right now is close to ideal until, 1) lipo batteries change shape or 2)motors change shape.
Its not the "ideal" layout... its simply become the most accepted due to perceived success... 5 minutes with a set of scales, a battery and the electronics will tell you its hardly a ideal layout... though I will admit LiPo's make it better...

Before the 415 won the worlds (by accident really) everyone was convinced that shaft drive was the only way to go and MOST of the major manufacturers had a shaft drive car as their primary product... after the unforeseen success of the 415 (most of the factory Tamiya drivers were running EV0 3's) it was suddenly back to belt drive and the "new" battery-down-one side layout...

... and its been stuck like that ever since, not because its the best but because none of the major manufacturers want to risk the money, in a still very competitive, if slightly shrinking, TC market, developing a car radically different to that of their competitors... and its left up to smaller niche manufacturers like Tigermoth Racing to try something different...

Mid mount has been tried several times before.. the orginal Losi Street Weapon was basically mid mount and I remember a Ofna/Hong Nor car in the mid-90's as well... and I am sure there are others... yes the main downfall is the battery being so far back but again, LiPo and their lower weight should alleviate some of that...
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Old 11-15-2009, 04:37 PM   #10
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Isn't original Losi JRX-S Pro a 'mid-motored' car

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Old 11-16-2009, 01:47 AM   #11
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Not mid motored, but I did like the balance of the HPI Pro 2 if you're looking at cars that used a saddle pack.

Was pretty reliable too, didnt break anything on mine when I raced it many many years ago.
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Old 11-23-2009, 06:53 PM   #12
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Here's my solution. Still needs tweaking a bit.
Attached Thumbnails
Pros and Cons - Mid motored TC's-car-001.jpg   Pros and Cons - Mid motored TC's-car-002.jpg   Pros and Cons - Mid motored TC's-img_0235.jpg   Pros and Cons - Mid motored TC's-img_0236.jpg  
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Old 11-23-2009, 07:51 PM   #13
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And of course, there's always THIS....
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Pros and Cons - Mid motored TC's-ta05v.2chassis1..jpg  
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Old 11-23-2009, 08:49 PM   #14
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Would a mid-motored car not rotate better on a technical track? With a Durango-style battery placement and a saddle pack Lipo, this could possibly be one of the better configurations.

IMO, the JRX-S and the JRX-S Type R don't have the central motor position quite right. It would be more beneficial to have a higher layshaft and be able to have longer arms, thus making the car roll better (which is what we need with rubber tire sedan racing).

Also, before CG gets mentioned, I would like to say that without "lay down" shock mounts like on the Tigermoth your highest point is always your shock tower. The weight of a spur gear, layshaft and two belts would affect the way the car rolled by very little.
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Old 11-24-2009, 01:26 AM   #15
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Quote:
Originally Posted by Danny-b23 View Post
Would a mid-motored car not rotate better on a technical track? With a Durango-style battery placement and a saddle pack Lipo, this could possibly be one of the better configurations.

IMO, the JRX-S and the JRX-S Type R don't have the central motor position quite right. It would be more beneficial to have a higher layshaft and be able to have longer arms, thus making the car roll better (which is what we need with rubber tire sedan racing).

Also, before CG gets mentioned, I would like to say that without "lay down" shock mounts like on the Tigermoth your highest point is always your shock tower. The weight of a spur gear, layshaft and two belts would affect the way the car rolled by very little.
You should look at the HPI Pro3. Central battery and motor, and long arms too (the arms are mounted inboard of the diff pulleys.

Unfortunately HPI got the materials badly wrong on that car, and even when they got the materials right it just wasn't as fast as the Pro4 they built to replace it (which was basically a refined TC3).

Although the Pro3 was one of the easiest cars to drive for club racers that I have seen.

Grizzbob - The TA05 hangs the motor way out and the cells are offset well towards the rear. With heavy NiMH, the car was very heavy on the RR corner. I've seen one with LiPo and the balance was much better, it seemed that with that layout the car really came alive. Is the V2 better balanced? If our aim is to get the centres of mass closer to the centreline of the car, TA05 is not really the solution.

ads0021 - Nice work. An XRAY 009/T1 hybrid with inline cells? Very nicely realised. The issue people have always pointed to with these designs is that the car has a lot more inertia to pitch than it does to roll, which may be why the wider and shorter layout of the electrics in the normal 009 became the preference with NiMH. The significantly lighter weight of LiPo is an opportunity to try some new solutions (or revisit some old ones!).
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