When is it time to replace dog bones?

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Horatio said:
Blades or pucks are the way forward. There's no need to re-invent stuff that's already been well proven on 1/10th scale buggies and touring cars. It just needs to be replicated for 1/8th.

MOD speed have been using 'pucks' - which are essentially the same thing. They're made for centre driveline and axles.

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This means the shafts can be made from lighter material. Ditto the input/output cups.

Lower rotating mass.
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I see MIP also has the pucks without the driveshafts and cup.
https://www.miponline.com/mip-pucks-rebuild-kit-no-1-5-pucks-17045
 
But then they couldn't sell you a new set of drive cups and dogbones every 6 months. Also I'm not sure I would trust an aluminum shaft and thinner drive cups with the power system I'm running.

EDIT I couldn't use those because the screw heads would interfere with the motor. There is about 3mm of space between the rear outdrive and the side of the motor.
 
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Horatio said:
3D printed input/outputs would be awesome if they were just as durable as machined items. Especially if they were cheaper.
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General Electric uses 3D printed metal parts in jet engines now. Even if 3D printed tool steel isn't as strong as machined tool steel I bet it's still wears better than spring steel which from what I have read about it actually doesn't make a good bearing steel.
 
Atomic Skull said:
General Electric uses 3D printed metal parts in jet engines now. Even if 3D printed tool steel isn't as strong as machined tool steel I bet it's still wears better than spring steel which from what I have read about it actually doesn't make a good bearing steel.
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I'm sure advances in 3D printing are way ahead of what I'm currently aware of.

But the solution to modern Truggy outdrives already exists - merely by revising outdrives slot thickness and using delrin blades.

MOD/MIP type puck system is slightly proud of the outdrives (which may not suit everyone's setup) but a scaled up version of blades certainly would work as they are contained within the outdrive's dimensions.

Schumacher, Corally Assassin blades, RC Lab - all used to make these around 2004. They just need to be scaled up to suit our needs and the outdrive slots filed out slightly accordingly to accommodate them.

I've a good mind to fabricate my own just to prove the point.

Machining the hard spring steel outdrives would require some decent tools, but perhaps opening out the slots on the old black outdrives would be easier.

Dogbone pins and outdrives would then pretty much last forever. Only the blades would need replacing, costing pennies.
 
Atomic Skull said:
I just had an idea earlier today, what about drive cups 3D printed from tool steel? Yes this is a thing.

https://www.pcbway.com/rapid-prototyping/3d-printing/metal/Tool-steel/
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The problem I’ve always had with 3d printing is layer adhesion. Gluing layers together is only so strong. Machining from one “billet” material gives you equal strength in every direction without the part being weaker in one axis due to layer adhesion issues.

You might get away with printing a small “donut” with a 3d printer if you print it correctly. I wouldn’t print a drive cup though. The printers that can print those materials are expensive making the parts expensive.
 
If you can find a 3D printer spool with the same material qualities as delrin - ie hard - yet flexible enough to fit over a dogbones without snapping - self lubricating and very durable - you just need to 3D print this -

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at a size that can pop over the end of our 8mm dogbone ends.

The cushion is likely only going to be about 3mm wider than the pin itself.

Then really all you need to decide is how much thicker you need the slots to be. They should be a close clearance fit - play isn't required. But the blades should be able to slide in and out of the slot as the suspension articulates.

The slot needs to be precisely widened such that it's kept very central so as not to induce balance or vibration issues.

Changing Pins with a pressing tool, whilst useful, is a reactive measure that only addresses 1 half of the problem.

Pin cushions would be a preventative cure, with a holistic solution that addresses the issue of the input/output drive wear as well, which not only are (by far) the more expensive part to replace, but also require more wrenching to remove.

From a racing perspective, smoother, less notchy transmission results in better handling during cornering - especially when powering out of low grip corners.

Modern touring cars are using bearings - rather than pucks - similar to Scorched Parts 'Trident Drive'.

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I would happily take a delrin cushion over a small bearing for basher use, as they require virtually zero maintenance.

Bearings make more sense on speedrun machines or touring cars.
 
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There are even self lubricating plastic like bushings that would be ideal. They are used on some mountain bikes suspension pivots. The same is true of pedal bushings. I forget the trade name, but they are ideal for high load, low speed use, as is what happens in the dog bone sliding surface area.
 
danl said:
The problem I’ve always had with 3d printing is layer adhesion. Gluing layers together is only so strong. Machining from one “billet” material gives you equal strength in every direction without the part being weaker in one axis due to layer adhesion issues.

You might get away with printing a small “donut” with a 3d printer if you print it correctly. I wouldn’t print a drive cup though. The printers that can print those materials are expensive making the parts expensive.
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Metal is different these are industrial machines that start at 6 figures not hobbyist tech that has to be affordable by individuals. It's printed either by melting powder layer by layer with a laser or building up a "green" component which is then fused in an oven, or a cast is made from a 3D printed negative that is then melted away from the completed mould.

Also, PCB Way, JLC PCB and others can make 3D printed plastic on SLS (selective laser sintering) or high resolution photo resin printers using high strength resins with durability in the same ballpark as injected molded plastics for pretty reasonable cost (a few $$ per part).

Industrial 3D printing is a whole different world from hobbyist stuff because the machines and technology are more advanced.
 
Atomic Skull said:
I don't want to sound pessimistic but that could very well be the problem drive train components are probably a cash cow.
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Sadly, I think you're right.

Would it be possible to 3D print with a material with POM-like qualities, ideally very similar to Delrin?
 
Horatio said:
Sadly, I think you're right.

Would it be possible to 3D print with a material with POM-like qualities, ideally very similar to Delrin?
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Don't think so but you could have POM parts machined by JLC PCB or PCB Way. I'm not sure what the pricing is like on machined parts from them though.
 
There's another very simple solution they could use. Whatever stuff Hobao uses to make their drive cups and pins, just use that.
 
As a person who has used both shaft and belt driven cars for the past 40 years, to sum up:

There are specific, niche areas within RC cars where belts offer up handling advantages that mitigate any friction related / rolling resistance disadvantages that belts inherently have.

Touring cars - the layout of a modern, competitive chassis will feature 2 belts, to position the motor favourably.

In almost every other instance, machined gears are inherently less lossy.

A fuller answer could be availed here, but the debate about belt Vs shaft was tucked up over on RCtech after years - identical shaft driven car tested against belt driven car with the same battery, ESC and motor.

Current draw with belt driven cars will be higher, which matters on spec classes. It matters less with modern cars running mod and more power than they ever need.

As belts increase speed, oscillation occurs, impacting efficiency. Mitigating belt slip requires tensioners - again - impacting efficiency.

Chippings, fluff etc can get into pulleys etc unless tracks are scrupulously clean, or unless proper cases fully protect the system for off road rigs.

There's no replacement for pucks/blades - besides - you still need driveshafts to the wheels.

Unless you use direct drive to the wheels - transmission free. That's probably the most efficient alternative. 🤩
 
Horatio said:
As a person who has used both shaft and belt driven cars for the past 40 years, to sum up:

There are specific, niche areas within RC cars where belts offer up handling advantages that mitigate any friction related / rolling resistance disadvantages that belts inherently have.

Touring cars - the layout of a modern, competitive chassis will feature 2 belts, to position the motor favourably.

In almost every other instance, machined gears are inherently less lossy.

A fuller answer could be availed here, but the debate about belt Vs shaft was tucked up over on RCtech after years - identical shaft driven car tested against belt driven car with the same battery, ESC and motor.

Current draw with belt driven cars will be higher, which matters on spec classes. It matters less with modern cars running mod and more power than they ever need.

As belts increase speed, oscillation occurs, impacting efficiency. Mitigating belt slip requires tensioners - again - impacting efficiency.

Chippings, fluff etc can get into pulleys etc unless tracks are scrupulously clean, or unless proper cases fully protect the system for off road rigs.

There's no replacement for pucks/blades - besides - you still need driveshafts to the wheels.

Unless you use direct drive to the wheels - transmission free. That's probably the most efficient alternative. 🤩
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I 110% agree with everything you're saying here, but then I'll always scratch my head when I see an RC10 running
 
AggyMi said:
I 110% agree with everything you're saying here, but then I'll always scratch my head when I see an RC10 running
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I remember the RC10 when it first came out. It was Team Associated's answer to highly modified Tamiya SRB buggies (essentially Sand Scorchers modified for racing) that dominated everything for about 4 years.

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I know - crazy right?! 😅

Team Associated was like - 'how do we make this - only more better?'. 🤣

So they were liking this way of thinking:

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And the OG RC10 was born in 1984. Here's the very, very first ever RC10:

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Sorry to disappoint the Halls brothers - you'll note the 'upside down' shocks were normally mounted this way. It was standard practice and helped ensure that shocks didn't leak. Turning them shaft side down happened later, as it was found to improve the unsprung weight, which makes suspension more effective.

In this museum piece, I'm not sure where their mechanical speed controller is. In this very early hand made prototype, perhaps they were yet to produce it?

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Fun fact! It was the legendary Kyosho Scorpion, heavily modified, that broke the SRB's winning streak during the 1983 ROAR National Championships. It was not the RC10!

The first RC10's weren't available until the end of 1984, but it was 1985 that saw RC10's win both ROAR National Championships and 1985 IFMAR Worlds 2WD Stock. 😎
 
Horatio said:
In almost every other instance, machined gears are inherently less lossy.
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Fun fact, belts are less lossy at high RPM than gears are. With belts friction remains constant regardless of RPM, with gears friction increases as RPM does. Also belt drive systems often feature fewer stages than a gear system does because you can change the direction of the rotation up to 90 degrees by twisting the belt, which further reduces losses at running speed.

This has been an ongoing war in RC helis for a long time, torque tube (tail driveshaft) driven off the main gear (either a layshaft and pinion that drives a bevel gear or a bevel gear driven by a crown gear on the mainshaft) that drives a pair of miter gears in the tail vs direct driven belt tail with a pulley on the mainshaft and the belt twisted 90 degrees inside the boom to drive a pulley on the tail rotor shaft so that no change of direction of rotation is needed, with both sides arguing that their side has less friction losses. The engineering books say belts have less losses overall but the torque tube guys were having none of it. Went on for nearly 20 years, in end tail drive belts won out I don't think there has been a new torque tube heli released in the past 5 years all brand new designs (as opposed to new improved versions of old existing designs) used stacked frames and a tail drive belt now.

Of course a car that runs at lower and changing RPM a lot of the time is a different situation than a helicopter where the RPM is more or less constant and high (typical tail RPM on a 700 size helicopter is around 9000 RPM.
 
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Atomic Skull said:
Fun fact, belts are less lossy at high RPM than gears are. With belts friction remains constant regardless of RPM, with gears friction increases as RPM does. Also belt drive systems often feature fewer stages than a gear system does because you can change the direction of the rotation up to 90 degrees by twisting the belt, which further reduces losses at running speed.

This has been an ongoing war in RC helis for a long time, torque tube (tail driveshaft) driven off the main gear (either a layshaft and pinion that drives a bevel gear or a bevel gear driven by a crown gear on the mainshaft) that drives a pair of miter gears in the tail vs direct driven belt tail with a pulley on the mainshaft and the belt twisted 90 degrees inside the boom to drive a pulley on the tail rotor shaft so that no change of direction of rotation is needed, with both sides arguing that their side has less friction losses. The engineering books say belts have less losses overall but the torque tube guys were having none of it. Went on for nearly 20 years, in end tail drive belts won out I don't think there has been a new torque tube heli released in the past 5 years all brand new designs (as opposed to new improved versions of old existing designs) used stacked frames and a tail drive belt now.

Of course a car that runs at lower and changing RPM a lot of the time is a different situation than a helicopter where the RPM is more or less constant and high (typical tail RPM on a 700 size helicopter is around 9000 RPM.
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This statements about belts 'being more efficient under load' or 'as rpm increase' = fallacy.

Time to deep dive....🤣

The truth is, belts oscillations create additional losses as rpms increase. Furthermore, belts inherently want to escape the pulleys that they're turning.

Helicopter tail rotors don't compare well with 4wd car transmissions, although I can see why it would have sparked debate for heli pilots around the globe - and for all the same reasons.

We may as well introduce tape decks into the mix. Or record players. They're too entirely different to compare objectively with our RC cars.

We could also introduce bicycles. Again, belt drives are a popular choice, but not because they're more efficient or quicker - but because they're low maintenance and don't require lubrication. They're actually harder to ride - fact. This hardly matters if you're powering your e bike though.

When we see a 1/8th scale belt driven car exceed 200mph - then we'll have something credible to compare and discuss. 😝

The only downside with well engineered geared solutions is transitioning torque through 90°, which incurs some loss - but less loss overall than all the friction, tensioners and stiffness associated with running a belt - usually multiplied by 2 in an RC car.

This was amply demonstrated in spec classes when the TC3 was released. It was untouchable. At a time when brushed motors and batteries struggled to give us the power we needed for 5 minutes of racing.

Things have changed - we have more power than we can sensibly use, so the return to belts in touring cars is more to do with optimising the chassis layout for weight distribution and lowest CoG possible for 2S racing, than it is for most efficient use of power, as is often purported by 'end users'. The problem is: it just isn't true!

After years of debate, a Dyno was used to test to 1/10th touring cars with identical motor, ESC and battery. One shaft driven car, one belt driven car.

The belt driven car drew more current at ANY given motor RPM, because there was greater load on the motor compared with the shaft driven car.

In my real world testing - my Schumacher Axis always used more juice out of my NiMH 3000 cells using Reedy MVP motors than my TC3 using NiMH and MVP motors. Every time.

My Tenth Tech Predator was blisteringly quick and hit higher top speeds Vs my Cat 3000, using Reedy 11 double motors and NiMH 3000 cells.

Shaft with bevel gears turning Crown gears Vs 2 belts turning 2 pulleys
To evaluate the efficiency of a dual belt system compared to a shaft with bevel pinions turning crown gears, we need to consider several factors, including friction losses, mechanical design, and the properties of the materials involved. Here’s a breakdown:

### Belt System:

1. **Friction Losses**: Belt drives typically have lower frictional losses compared to gearing systems, especially when using high-quality belts and pulleys. Efficiency can vary widely, often achieved in the range of **90% to 98%**, depending on the quality of the belt and the alignment of the system.

2. **Flexibility**: Belt systems are generally easier to install and adjust than gears. However, they can stretch and wear over time, which can lead to reduced efficiency.

3. **Slippage**: If not tensioned properly, belts can slip, which can lead to additional efficiency losses.

### Gear System (Bevel Pinions and Crown Gears):

1. **Friction Losses**: The efficiency of well-designed gear systems, especially bevel gears, can be high, typically ranging from **95% to 98%** as long as they are accurately machined and well-lubricated.

2. **Backlash and Alignment**: Gears can suffer from backlash and require precise alignment, which can introduce additional limitations if not managed properly.

3. **Durability**: Gears tend to be more durable and can handle higher loads without significant wear compared to belts. They are less susceptible to stretching or slipping.

### Conclusion:

1. **Most Efficient System**: In a refined system where both setups are optimized (high-quality belts/pulleys vs. high-quality gears), the **gear system** (bevel pinions turning crown gears) might edge out in terms of efficiency, particularly due to the potential for high mechanical efficiency (close to or over 98%).

2. **Considerations**: However, for specific applications, other factors such as weight, maintenance, noise levels, and operational environments might lead an engineer to prefer one system over the other. For example, belt systems can be quieter and provide shock absorption, while gear systems typically provide more precise torque transmission and less slippage.

3. **Final Choice**: If absolute efficiency under load is the primary concern and the application allows for the complexity of gears, the bevel gear system is often the more efficient choice. If flexibility, ease of maintenance, and simplicity of design are crucial, the belt system might be favored, even with a potential slight reduction in efficiency.

Anyone reaching the end of this post without lapsing into coma deserves a high five! 😅 Well done!
 
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