Scratch build electric tethered car racer

[Roog]

You are doing a fantastic job with this man. One thing I noticed from the get go is your surface finishes look great. Especially for not having flood coolant. Your design is solid too. One thing I excelled at, and why I progressed to the prototype work in every shop I was at, was because I could see areas of fixtures that would be at risk of mechanical loads and stresses. Some of the parts I made were ones people thought we couldn't do til I designed a fixture. So when I point out things on your build, it's just me being a bit over analytical. You've done a great job at building something not many people could build.

I genuinely appreciate your comments, I know that there are things I could do better, mainly more accurate but also lighter! but my lack of experience with RC gear and machining means that I usually do things my way rather than the correct way.

It’s a bit like the way I use CAD, I create CAD drawings like a draftsman would create a physical drawing.

I am an engineer, an electrical and electronics one, but I also enjoy making machines.

My First job was to design control systems and program industrial machines in automated factory production lines, that got me into moving structures, hydraulic lifting bridges and during the 90’s I got drawn into the general construction industry, where I mainly specialise in power engineering and healthcare buildings. This is a far cry from the fun I had designing, making and commissioning factory machinery for sale. I tend to do ‘troubleshooting’ these days.

 

[WickedFog]

I genuinely appreciate your comments, I know that there are things I could do better, mainly more accurate but also lighter! but my lack of experience with RC gear and machining means that I usually do things my way rather than the correct way.

It’s a bit like the way I use CAD, I create CAD drawings like a draftsman would create a physical drawing.

I am an engineer, an electrical and electronics one, but I also enjoy making machines.

My First job was to design control systems and program industrial machines in automated factory production lines, that got me into moving structures, hydraulic lifting bridges and during the 90’s I got drawn into the general construction industry, where I mainly specialise in power engineering and healthcare buildings. This is a far cry from the fun I had designing, making and commissioning factory machinery for sale. I tend to do ‘troubleshooting’ these days.

That is the one thing I could never grasp was electrical stuff. My dad was a whiz with it. He dabbled in tv repair for a bit when I was a toddler I believe. He also built his own circuit boards and gizmos to hop up his CB radios. His car CB could reach way the hell out there, and was, I am sure, completely illegal, because he added some extra crystals to it that were hooked up to a hidden switch. No idea what that did, but I know his buddies were in awe when he showed em what it could do. I do know back then, it could pick up the police band, and him being a cop for awhile, he understood all their codes and stuff.

Looking forward to hearing about the next run. Hopefully a video too. This is one of my favorite projects on here.

 

[Roog]

That is the one thing I could never grasp was electrical stuff. My dad was a whiz with it. He dabbled in tv repair for a bit when I was a toddler I believe. He also built his own circuit boards and gizmos to hop up his CB radios. His car CB could reach way the hell out there, and was, I am sure, completely illegal, because he added some extra crystals to it that were hooked up to a hidden switch. No idea what that did, but I know his buddies were in awe when he showed em what it could do. I do know back then, it could pick up the police band, and him being a cop for awhile, he understood all their codes and stuff.

Looking forward to hearing about the next run. Hopefully a video too. This is one of my favorite projects on here.

Yes electricity is quite magical, but for me that was ruined when as a kid I started breaking open old electronic components to see what was inside, and the ‘nothing to see here’ cured me. At least the science in so far as it applies to electricity and electronics works well :0)

Electronics isn’t the hobby it once was, when you made things because you couldn’t afford a manufactured item. Now it seems I can buy a module that will do almost everything I want for a handful of $.

As for video of our car runs, the last runs were recorded by one of the members using a camcorder on a tripod, I’ve not seen a traditional camcorder for quite a while, hopefully the footage will surface at some point and I’ll stick it on YouTube.

 

[WickedFog]

We do all our video with my phone on a little tripod.

 

[Roog]

We do all our video with my phone on a little tripod.

Quite so, a rigid tripod is probably the most important photographic/video accessory you can buy, just slightly taken aback at seeing the camcorder :0)

On the subject of video, I recently bought a low cost drone, just for a bit of fun. I would like to take video of the track from above the track to get an alternative perspective. On my last outing the wind was very blustery, not a great time to get to grips with another hobby, so I abandoned my flight practice, I must have another go next time.

 

[WickedFog]

Quite so, a rigid tripod is probably the most important photographic/video accessory you can buy, just slightly taken aback at seeing the camcorder :0)

On the subject of video, I recently bought a low cost drone, just for a bit of fun. I would like to take video of the track from above the track to get an alternative perspective. On my last outing the wind was very blustery, not a great time to get to grips with another hobby, so I abandoned my flight practice, I must have another go next time.

I've always wanted one of the small DJI drones. They are so stable, even in wind. Add with the video stabilization on top of that and they produce some really crazy good video. I can just never save up enough to buy one before other things use up the funds.

 

[LibertyMKiii]

Really great work on this project.
It is rather rare to see someone in this hobby make things from scratch. I built a custom car also belt drive with a carbon body but don't have the balls to drive it with the risk of a crash.

For some reason these tethered RC car tracks are only in EU. I have not seen it done in the US at least in the last decade or 2.

I am sure you have looked a little at what standard rc cars are doing in speed runs and how they run foam tires. What sort of RPMs can these rubber tires hold?
I believe the foam tires are holding up to 17-21k rpms.

 

[Roog]

Really great work on this project.
It is rather rare to see someone in this hobby make things from scratch. I built a custom car also belt drive with a carbon body but don't have the balls to drive it with the risk of a crash.

For some reason these tethered RC car tracks are only in EU. I have not seen it done in the US at least in the last decade or 2.

I am sure you have looked a little at what standard rc cars are doing in speed runs and how they run foam tires. What sort of RPMs can these rubber tires hold?
I believe the foam tires are holding up to 17-21k rpms.

Thank you @LibertyMKiii
Ah, the scratch build thing is because electric drive tethered cars are quite new, and kits of parts are non existent, plus I am quite tight with money so the thought of parting with money would encourage me to have a go.

I calculated that 100mph would be about 15,000rpm, judging from the tire damage I have experienced I think a degree of wheel spin is happening but I was not aware of rising tone from the motor.

It has crossed my mind that fast rc cars seem ok with their tires, but I’m guessing they don’t suffer the forces that tethered cars do. To be fair two out of three tires on my car were OK, but it takes just one to go imbalanced and all hell breaks loose.

It is interesting what you say about tracks in the US, I believe tethered car racing started in the US back in the 1930’s. It was big in the UK in the 1950’s and there are now very few tracks about, it is just a lucky coincidence that there is a small track just 20mins drive from where I live, so it seemed rude not to join in!

 

[LibertyMKiii]

Thank you @LibertyMKiii
Ah, the scratch build thing is because electric drive tethered cars are quite new, and kits of parts are non existent, plus I am quite tight with money so the thought of parting with money would encourage me to have a go.

I calculated that 100mph would be about 15,000rpm, judging from the tire damage I have experienced I think a degree of wheel spin is happening but I was not aware of rising tone from the motor.

It has crossed my mind that fast rc cars seem ok with their tires, but I’m guessing they don’t suffer the forces that tethered cars do. To be fair two out of three tires on my car were OK, but it takes just one to go imbalanced and all hell breaks loose.

It is interesting what you say about tracks in the US, I believe tethered car racing started in the US back in the 1930’s. It was big in the UK in the 1950’s and there are now very few tracks about, it is just a lucky coincidence that there is a small track just 20mins drive from where I live, so it seemed rude not to join in!

Traction is tricking due to the forces acting on the car. Adding wings for downforce likely is not ideal. Also seems to not be necessary based on historical 200+ mph cars I looked at.

When I looked at your build the first thing I thought was that a Castle MMX8s ESC would be really helpful with the great data logging it has. You would be able to to see wheelspin with tracking the RPMs, voltage etc.

I recently got more into RC boats because a decent size pond is a 4 min walk from my house, so I fully understand what you mean when there is a nice spot close by.

 

[Roog]

Traction is tricking due to the forces acting on the car. Adding wings for downforce likely is not ideal. Also seems to not be necessary based on historical 200+ mph cars I looked at.

When I looked at your build the first thing I thought was that a Castle MMX8s ESC would be really helpful with the great data logging it has. You would be able to to see wheelspin with tracking the RPMs, voltage etc.

I recently got more into RC boats because a decent size pond is a 4 min walk from my house, so I fully understand what you mean when there is a nice spot close by.

Regarding the tracking ESC, if I can stop worrying about the tires escaping I could concentrate on building speed more progressively, It would be very helpful and interesting to get that feedback, although the escalating costs and complexity are drifting away from the intended simplicity of the hobby. The geek in me loves the idea.

yes finding a good pond/lake that’s normally a challenge. As a teenager I was able to use the pond and latterly the lake at two of Bath’s universities, one on King Charles property! He understandably didn’t allow IC power due to the wildlife.

We also have a disused airfield about 5 miles away which we used for RC and control line model planes and a decent hill for slope soaring, I’ve been very lucky.

 

[Roog]

Went to the track today, all was going smoothly then,…..

I brought it to rest just as you seen the picture above on two wheels.

I got up to 65mph, (another new track record!) then there was a noise and the outside rear tire flew off.

It appeared to fly off as one piece and disappeared into a hedge, there seemed little hope of finding it, I hope the sheep in the next field don’t find it either.

I think the tire split, because it came off in one piece and I'm fairly sure that it didn’t just roll off the rim.

I continued to run using my previous surviving home made tire and wheel. We noticed that the car would make a strange rumbling noise at around 60mph, perhaps it’s a belt resonance? One suggestion is to get a new motor pulley of a larger diameter to put the belt through a less tight bend, another thought is whether the motor is cogging I.e. the rotor can’t keep up with the rotating magnetic field?

Is this a thing with brushless motors?

 

[WickedFog]

One suggestion is to get a new motor pulley of a larger diameter to put the belt through a less tight bend,

You might want to get some delrin or nylon (self lubricating) and make that belt guide like I showed you earlier in this thread. You might even add external guides. It very well could be the tight radius of the motor pulley causing belt flutter. If you can get the pulleys closer to the same diameter, that may resolve some of that. Have you not ran it up to speed on a bench to see what issues you may have?

another thought is whether the motor is cogging I.e. the rotor can’t keep up with the rotating magnetic field?

Is this a thing with brushless motors?

Not after getting past the initial startup, no. You could try a sensored setup if you can't figure out any other causes. But I don't think it's the motor.

As for your tire flying off, i was afraid of that. You're going to have to bite the bullet and encompass those tires into a reverse cone shape with your wheels. If it were me, I'd only leave about a centimeter of the tire exposed. The rest would be encapsulated in an aluminum housing.

 

[Roog]

You might want to get some delrin or nylon (self lubricating) and make that belt guide like I showed you earlier in this thread. You might even add external guides. It very well could be the tight radius of the motor pulley causing belt flutter. If you can get the pulleys closer to the same diameter, that may resolve some of that. Have you not ran it up to speed on a bench to see what issues you may have?

Not after getting past the initial startup, no. You could try a sensored setup if you can't figure out any other causes. But I don't think it's the motor.

As for your tire flying off, i was afraid of that. You're going to have to bite the bullet and encompass those tires into a reverse cone shape with your wheels. If it were me, I'd only leave about a centimeter of the tire exposed. The rest would be encapsulated in an aluminum housing.

Oh, you posted this in the wrong thread
Click to expand...

Thanks for your thoughts on motors, I suspect the belt myself.
Funny thing is I followed the advised tire fixing to the letter.

I have another plan for the conveyor belt tires but it involves making new hubs and much working of the rubber.

 

[WickedFog]

I have a feeling if you don't grip those conveyor belt tires very close to the outer diameter you are going to be forever fighting them. And doing so with holes around the outer lip, if that is what you are considering, is just going to create weaker areas in between the bolts that will still fly out. So face grooves in the contact sides of the wheels, leaving thin rings to squeeze and grab the rubber, will be your best, and likely only solution.

I seem to remember the cone shaped wheels cannot be found anymore right? I am sure somebody sells them. Get me a few pics from different angles of your cone tire you still have. I'll see what I can find. Because I really think so far, they were your best solution to the problem. With encapsulated wheels, they simply cannot fly apart.

One other option, smaller diameter tires, taller gearing. That will create less centrifugal force on the tires.

One thing I just thought of...
Your car is travelling in a circle. Your tires naturally want to travel a straight line. I wonder since your car is tethered, if the tire isn't walking itself outward and folding over once it reaches the threshold of the tire's ability to maintain shape, and pulling itself out of the wheel, rather than centrifugal force being the main cause. A bench test might prove this theory. If that is the case, simply adding larger diameter aluminum hubs, with less tire exposed, may solve the problem.

A severely exaggerated view of what I mean. The tire wanting to go straight. But the tether pulls it around an arc. So the tire is always fighting the curve. And the sidewsys centrifugal force is trying to fold the tire outward as well.

So in other words, I wonder if your tire isn't also turning into a bowl shape as it goes around the track.

 

[WickedFog]

Sorry... my mind is in engineering mode. Another reason the cone tires are a great idea...

As your conveyor belt tires expand outward, even ever so slightly, the rubber is thinning. That creates less grip by your wheels. Which in turn gives the rubber more leeway to expand, making them thinner, allowing them to expand, etc, etc, etc.

The cone shaped tires would have to nearly liquify to squeese all that material through the funnel shaped cross section that the encapsulated wheels would provide. As the tires try to expand, the force of the wheel surfaces squeezes the rubber tighter and tighter.

 

[Doom!]

Congrats on the new track record Sorry about having to go back to the drawing board.

 

[Roog]

Congrats on the new track record Sorry about having to go back to the drawing board.

Yup its a right pain, cost is OK but the time required is stressing me a bit, I have other important stuff to do on real vehicles!

Responding to @WickedFog a moment back, I agree I don't want to puncture the tire anywhere that would just tear.

The retro wheels I used most recently are shown as mounted on modest hubs, image below taken from the parts page and very similar to mine (I followed their instructions to the letter) perhaps they are just not reliable at higher speeds, perhaps i got a bad'un, the other has survived as have two of my home made tires.

Another much sportier wheel looks like this, you can see a grove for the tire

These use 100mm dia. tires with a narrow tread area, in part for lower air resistance.

My issue is, even if I put cost to one side, the availability of these tires is uncertain. Yesterday I was given a contact in Ukraine as a source of the retro tires I used yesterday, I am happy to support him, but it is a bit remote and they didn't stand up to the pressures my car imposed on them so probably not a great option. I suspect this is why people make their own.

As @WickedFog days above I think a thin tire with rims which go close to the rolling diameter would be the most suitable.

Issue is, how to obtain/make such a tire?

I have thought about super gluing O-rings on a rim like they do with 'tubeless tires' on racing cycles but this doesn't 'feel strong enough' to me. Easy to make though!

Oh and I have ordered a 30T pully for the motor, that gives me a lower ratio of 3:4

 

[Roog]

OK here's a new train of thought, I now know from practical experience that making stuff that doesn't break apart when spun to to speed is hard!
So does someone already make "something which has to be spun up very fast without falling apart or injuring someone?" and "do some of these have a durable rubber finish?"

I wonder if their is mileage in adapting backing disks for sanders for example?

I note max safe speed ten thousand rpm, surely they must have a fair safety margin, good for 20 perhaps?

In fact anything which someone has already designed that doesn't break apart when spun up at speed might be a start?

BTW yesterday at the track side discussion drifted on to "how to use solid wheels?" perhaps I could bond a toothed belt to the circumference? just joking LOL!

 

[WickedFog]

This is kinda what I was trying to explain to you earlier about face grooves in the wheels. But that is more of a proud rib sticking up. If you had a rib like that close to the outer edge, then left just a little bit of your conveyor belt tire protruding, I think they would handle a lot more RPM.

I like the o-ring idea, but glue won't hold it at those RPM's. You'd want to machine a circular goove on the outside edge of the wheel halves to basically get around 75% (just guessing) wrap around the o-ring to prevent it from expanding outward. That would leave a fairly small contact patch. And you would want the heavy duty o-rings.

Convince them to coat the track with rubber, then just use aluminum wheels

 

[Roog]

This is kinda what I was trying to explain to you earlier about face grooves in the wheels. But that is more of a proud rib sticking up. If you had a rib like that close to the outer edge, then left just a little bit of your conveyor belt tire protruding, I think they would handle a lot more RPM.
View attachment 189687

I like the o-ring idea, but glue won't hold it at those RPM's. You'd want to machine a circular goove on the outside edge of the wheel halves to basically get around 75% (just guessing) wrap around the o-ring to prevent it from expanding outward. That would leave a fairly small contact patch. And you would want the heavy duty o-rings.

Convince them to coat the track with rubber, then just use aluminum wheels

My original wheels do have a 0.6 m deep lip at the edge which produced a pronounced indentation in the plain rubber tires, but clearly this isn’t enough, I did think about cutting a grove to align with the lip/groove but again I don’t think this will be enough. The clever fast tires trap a round ring inside the rim like an o-ring with just a thin tire protruding, making the wheel hub isn’t a problem but making or even buying the tires is.

I can see that tires are at the route to the solution

I am looking into seals and o-rings to see what is available there must be something out there.

And yes I agree, solid wheels are the future after all if it’s good for the full sized cars it must be good for the models,