Belt-drive transmission

[Mrgoodwrench35]

I've had some limited experience with rc belt drive and I was not impressed. The belt drive on the xmaxx is very poor, IMHO.

I am curious though, if a centrifical belt drive system, similar to the ones used on atv's and side by sides would have a valid use on RC. Seems like a variable gear ratio would be helpfull in on road applications.

 

[JCsRCcar]

In the automotive world (full size passenger cars) belt drives are used over gear drives simply because they are quieter compared to gear drives and compared to chain drives they don't stretch. In the RC car world this is not important. In the RC car world belt drives may be less susceptible to damages caused by sand to some degree. Otherwise belt drives may put more side load or strain on the front motor bearing due to the tension needed to keep the belt tight and not slip and they can be more complicated especially when you want to change the pinion gear. For efficiency I’m willing to bet the gear drive is more efficient but that would have be tested.

 

[bill_delong]

In the automotive world (full size passenger cars) belt drives are used over gear drives simply because they are quieter compared to gear drives and compared to chain drives they don't stretch. In the RC car world this is not important. In the RC car world belt drives may be less susceptible to damages caused by sand to some degree. Otherwise belt drives may put more side load or strain on the front motor bearing due to the tension needed to keep the belt tight and not slip and they can be more complicated especially when you want to change the pinion gear. For efficiency I’m willing to bet the gear drive is more efficient but that would have be tested.

I disagree, timing belts are a nightmare and will destroy an engine if you continue to drive a car as the timing belt begins to stretch and slip.

First time I experienced this was with a friends car which left us stranded in the snow up the mountains, but that's another story. The mechanic explained that if he stopped using the engine immediately when losing power then the belt could've been replaced without damage to the engine. A year later the same thing happened to my mom's car and I told her to immediately stop, it was a bad timing belt. Tow truck driver refused to tow the car without starting the engine and the belt snapped causing the engine to need replacement. I've helped close to a dozen other friends over the years prevent damage and encourage them to replace the timing belts before they snap. I've never once seen a timing chain ever snap.

There will always be a performance/maintenance sacrifice when switching from a gear design to belt design, no exception.

 

[Roog]

I disagree, timing belts are a nightmare and will destroy an engine if you continue to drive a car as the timing belt begins to stretch and slip.

First time I experienced this was with a friends car which left us stranded in the snow up the mountains, but that's another story. The mechanic explained that if he stopped using the engine immediately when losing power then the belt could've been replaced without damage to the engine. A year later the same thing happened to my mom's car and I told her to immediately stop, it was a bad timing belt. Tow truck driver refused to tow the car without starting the engine and the belt snapped causing the engine to need replacement. I've helped close to a dozen other friends over the years prevent damage and encourage them to replace the timing belts before they snap. I've never once seen a timing chain ever snap.

There will always be a performance/maintenance sacrifice when switching from a gear design to belt design, no exception.

Interesting point, every European car I have ever bought that had a timing belt seemed to have known issues with cars going back for changes and later models having different arrangements and different issues! Even my double chain drive jaguar had serious issues with timing chains letting go. I was glad it remained intact during my 10 year ownership of it.

 

[Lumikko]

A belt drive is less efficient when there’s no load or a low load. Anyone can see this by giving the wheels a spin when the car is on a pit stand.

Things change when you apply load and many critics of belt drives forget this. A belt drive under load is quite a bit more efficient than a shaft drive because of the bevel gears.

That’s not to say they are a better choice overall. Belts require the distance between the axles to remain constant to maintain proper tension. This is not compatible with the desire to tune the car with chassis flex. Shaft drives can be perceived as an easy solution with less hassle and adjustment.

Electric off-road 4WD world championships were won with belt drives for almost 20 years starting from the ’80s. My guess is that they offered the efficiency advantage necessary with the electronics of that era. When lipo batteries and brushless motors became the norm, the cars became so powerful that a bit of drivetrain efficiency could be sacrificed to get the option for increased chassis flex in return.

 

[JCsRCcar]

I disagree, timing belts are a nightmare and will destroy an engine if you continue to drive a car as the timing belt begins to stretch and slip.

First time I experienced this was with a friends car which left us stranded in the snow up the mountains, but that's another story. The mechanic explained that if he stopped using the engine immediately when losing power then the belt could've been replaced without damage to the engine. A year later the same thing happened to my mom's car and I told her to immediately stop, it was a bad timing belt. Tow truck driver refused to tow the car without starting the engine and the belt snapped causing the engine to need replacement. I've helped close to a dozen other friends over the years prevent damage and encourage them to replace the timing belts before they snap. I've never once seen a timing chain ever snap.

There will always be a performance/maintenance sacrifice when switching from a gear design to belt design, no exception.

You disagree but then bring up different and less relevant points about timing belts in an ICE. Timing belts for ICE engines, specifically dual overhead camshaft engines do not stretch like timing chains do, but they will break if they are not changed within the recommended interval suggested by the manufacturer. Many people don’t do the maintenance required because they either don’t know about it or don’t want to pay for it and just ignore it until it fails. My Toyota Tundra V8 timing belt had to be changed at 90k miles for example. Then there are freewheeling and non freewheeling engines where one will destroy the valves if the timing belt breaks and the other will not.

In the automotive world timing belts are lighter and less costly to manufacture compared to a timing chains and because timing belts don’t stretch, they also will not change the engine timing over time (towards retarded engine valve timing) due to that chain slowly stretching. Because timing belts are lighter they also have less reciprocal inertia which helps with fuel economy and makes the engine rev up faster too. Take it from a former ASE master certified technician here, I know a few things about timing belts.

BTW I’m not advocating for timing belts in RC cars. I don’t think they are better than gears.

 

[bill_delong]

You disagree but then bring up different and less relevant points about timing belts in an ICE.

You switched the topic to ICE and I was disagreeing about the durability of belts (specifically timing belts in the example I brought up) I prefer timing chains and this was a requirement before I bought my 2016 Colorado, I try to avoid timing belts because I prefer to do my own maintenance when possible and I don't have the skills/tools to replace a timing belt myself

...timing belts don’t stretch...

In the cases where I experienced a timing belt failure first hand, the engine would slowly get sluggish where top speed would diminish over the course of 10-15 seconds. This gave me the impression that the belt was stretching before it snapped. I am interested in hearing what is really going on during those precious 10-15 seconds as an indicator before the belt fails if it's not being stretched. I honestly have no clue, just what I saw first hand as an DIYer.

BTW I’m not advocating for timing belts in RC cars. I don’t think they are better than gears.

We are 100% on the same page here

 

[WickedFog]

In the cases where I experienced a timing belt failure first hand, the engine would slowly get sluggish where top speed would diminish over the course of 10-15 seconds. This gave me the impression that the belt was stretching before it snapped. I am interested in hearing what is really going on during those precious 10-15 seconds as an indicator before the belt fails if it's not being stretched. I honestly have no clue, just what I saw first hand as an DIYer.

Timing belts are fiber reinforced. Not sure how that could stretch unless it broke the fibers while the rubber remained intact.

 

[JCsRCcar]

Bill, to answer your middle question I have to assume the belt slipped or jumped a cog as it started to fail causing the loss of power before it finally broke.

So to get back on topic here (sorry) I think we all agree that belts have their place considered the comprises and are not the best fit for many RC drivetrains. I think Lumikko brings up some good points and his history on belt drives with RC is interesting. Considering back in the day most electric RC cars used brushed motors and NiCad or Nickel metal hydride batteries, drive line efficiency must have been more of a factor then.

 

[Brady Matthews]

Bill, to answer your middle question I have to assume the belt slipped or jumped a cog as it started to fail causing the loss of power before it finally broke.

So to get back on topic here (sorry) I think we all agree that belts have their place considered the comprises and are not the best fit for many RC drivetrains. I think Lumikko brings up some good points and his history on belt drives with RC is interesting. Considering back in the day most electric RC cars used brushed motors and NiCad or Nickel metal hydride batteries, drive line efficiency must have been more of a factor then.

Thank you, I now see why people don't like belt-drives in RC cars.

 

[Lumikko]

I’m not a touring guy but I hear belt drives are still popular in those things. They say it affects the feel because backlash is reduced and hitting the ends of the backlash is softer compared to shaft drive. They don’t do bumps and jumps so the rigid chassis required by the belt is not an issue.

Another thing I’m not is a highly skilled driver. I could probably drive a belt wheeler buggy or a shaft touring car and not notice anything out of the ordinary. Except the smooth sound of belt drive, gotta love it!

Timing belts on cars with IC engines… They are cheaper and have other advantages over other solutions but can fail in a snap. You can greatly reduce this risk by observing both the time and odometer intervals for changing it. Also, an interference engine (piston and valves occupy the same space at different times) can seriously fail if the belt snaps. Non-interference engines don’t have this problem. If a timing belt is used until failure, the teeth on the belt will get worn and it will probably exhibit some symptoms before failure. Skipping just one tooth will cause the engine to run (if it runs at all) in a way that will not go unnoticed!

 

[Mrgoodwrench35]

In the automotive world (full size passenger cars) belt drives are used over gear drives simply because they are quieter compared to gear drives and compared to chain drives they don't stretch. In the RC car world this is not important. In the RC car world belt drives may be less susceptible to damages caused by sand to some degree. Otherwise belt drives may put more side load or strain on the front motor bearing due to the tension needed to keep the belt tight and not slip and they can be more complicated especially when you want to change the pinion gear. For efficiency I’m willing to bet the gear drive is more efficient but that would have be tested.

The automotive industry uses belt drive transmissions because they're cheap and light, causing less drag on underpowered engines. NOT because they are quieter. Have you ever heard anyone say 'gosh, my transmission sure is loud' ? No, and neither has an auto manufacturer.

Timing belts are great, as long as you service them as intended. They most definately do stretch, just like any component made from rubber. The nylon reinforced belts last longer, but they still stretch. And yes, enough to effect valve timing. I've changed thousands of timing belts over the years and most of them were stretched. So to say they don't stretch is, well, a stretch.

 

[Lumikko]

The perceived stretch could be belt slackness because of wear on the sprockets and belt teeth. Nitpicking? Maybe. Also, I could be wrong.

None of them are made from just rubber, though. The elasticity of that material is not a factor.

 

[Mrgoodwrench35]

I've never seen sprockets wear to any measurable degree. Not the toothed side anyway. Variable cam gears wear internally but that's a different story.

The stretch I'm referring to is the overall length of the belt, not tooth wear. over the weekend, I replaced the timing belt in am old Honda accord 2.3. when I spun the engine over to line up the marks for belt removal, with the cam lined up, the crank was off just over a tooth with no slop in the belt. That's stretch. granted the belt was 20 years old and had 225k on it, bit still.

 

[Lumikko]

the belt was 20 years old and had 225k on it

All I can say is funny stuff happens when you grossly disregard maintenance.

 

[Mrgoodwrench35]

All I can say is funny stuff happens when you grossly disregard maintenance.

Agreed. The recommended interval is 80 or 100k so yeah, it was a little overdue. The belt looked suprisingly good for its age though.

 

[Chubaka]

I’m not a touring guy but I hear belt drives are still popular in those things. They say it affects the feel because backlash is reduced and hitting the ends of the backlash is softer compared to shaft drive. They don’t do bumps and jumps so the rigid chassis required by the belt is not an issue.

Another thing I’m not is a highly skilled driver. I could probably drive a belt wheeler buggy or a shaft touring car and not notice anything out of the ordinary. Except the smooth sound of belt drive, gotta love it!

Timing belts on cars with IC engines… They are cheaper and have other advantages over other solutions but can fail in a snap. You can greatly reduce this risk by observing both the time and odometer intervals for changing it. Also, an interference engine (piston and valves occupy the same space at different times) can seriously fail if the belt snaps. Non-interference engines don’t have this problem. If a timing belt is used until failure, the teeth on the belt will get worn and it will probably exhibit some symptoms before failure. Skipping just one tooth will cause the engine to run (if it runs at all) in a way that will not go unnoticed!

Defiant would be one to talk to. He has belt and shaft driven nitro rs4s. I never ran a belt. I will say those belt cvt trannys suck though.

 

[Grizz03]

I believe in everything stretches, however minute that may be.

I've never seen sprockets wear to any measurable degree. Not the toothed side anyway. Variable cam gears wear internally but that's a different story.

The stretch I'm referring to is the overall length of the belt, not tooth wear. over the weekend, I replaced the timing belt in am old Honda accord 2.3. when I spun the engine over to line up the marks for belt removal, with the cam lined up, the crank was off just over a tooth with no slop in the belt. That's stretch. granted the belt was 20 years old and had 225k on it, bit still.

That definitely was a ticking time bomb, especially for an interference engine. That's half a tooth at the cam. It's amazing how much these variable cam timing (VCT) engines can adjust for with no noticeable loss in performance. This type of technology is probably part of the reason why most don't understand the value of maintenance and we've become a throw away society.

 

[WickedFog]

I would again argue that timing belts are reinforced with fiberglass and or kevlar typically, depending on how much money you spend on them. Having worked for a company that made carbon fiber, kevlar, and fiberglass materials, I can tell you for certain those materials do not stretch.

I would also argue that what anyone is suspecting to be stretching is simply the inside diameter and the teeth of the belt wearing, which would make one believe the belt has stretched. The teeth may appear to still be fully engaged in the gear, but what you can't see is that the teeth of the belt are designed for an interference fit. A worn belt may still engage the teeth, but the loss of material over time will make the teeth more of a slip, or looser fit. There is of course going to be wear on the pullies as well, making it seem even more like the belt has stretched.

Just my thinking. No expert, but Kevlar and fiberglass simply do not stretch. Especially in the amount necessary to allow for a whole tooth out of timing.

 

[Mrgoodwrench35]

I'm not saying that Kevlar, nylon, or carbon fiber stretch. I am saying that a timing belt stretches. I don't care what it's reinforced with, it stretches.