Scratch build electric tethered car racer

[Roog]

Do you grind your own lathe tools? We had a few face groovers we made from HSS blanks.

Yes I do, I am thinking about putting a shallow grove in the tire to align with the clincher rim.

 

[ahr43]

Blimey, mate! Record first run out. Yeah, I's say that makes for a successful first session. Good show.

Always mods to make chasing that elusive mph figure. Looking forward to your follow-on runs.

Curious? Can you use the present body as a mold to pull one in Lexan? Reads like the gorilla in the room is body weight.

 

[Roog]

Blimey, mate! Record first run out. Yeah, I's say that makes for a successful first session. Good show.

Always mods to make chasing that elusive mph figure. Looking forward to your follow-on runs.

Curious? Can you use the present body as a mold to pull one in Lexan? Reads like the gorilla in the room is body weight.

Weight high up is definitely an issue, it was weird to see the car tilt up as the steel tether bar bent.
Having stripped the car back to make some changes it is apparent that the chassis rail is not a significant element of the all up weight, the wheels are heavy as are the motor and battery both as you might expect.

I am not sure if it will be worth making big holes in the angle chassis?

Parts strengthened and tether connection raised, I believe the tires are the weak point limiting top speed, I’ll try glue and see where I go from there

 

[WickedFog]

3m contact adhesive should work for glue I would think. I would scuff the rubber and aluminum up with sandpaper for it to get a good bite.

 

[Roog]

3m contact adhesive should work for glue I would think. I would scuff the rubber and aluminum up with sandpaper for it to get a good bite.

Good call re scuffing them surfaces. Lucky I have a couple of spare tires
I’ll look up 3M adhesive thanks

 

[Weezel]

Do you have any other rubber you could try making tires out of? It looks like the conveyor belt you are using has internal cording. I'm thinking that might be the cause of the ovaling. The cording is directional in the belting I've dealt with.

 

[Roog]

Do you have any other rubber you could try making tires out of? It looks like the conveyor belt you are using has internal cording. I'm thinking that might be the cause of the ovaling. The cording is directional in the belting I've dealt with.

Interesting point, initially I did look for purpose made tires, these are often expensive and require a very specific wheel profile, i was swayed by a club member to try the conveyor belt material as he had found it acceptable.

As It turns out, yesterday I was informed that they work ok up to a speed of around 50mph and even then when bonded on with some special 2 part glue designed for bonding metal to rubber! I am going to buy said glue and see how it works or not!

If this doesn't get me closer top my target speed I will consider buying purpose made tires and either modify my wheels to suit of make some more.

 

[Roog]

The ‘glue’ to bond my tires in has arrived, it’s an eBay purchase, amusingly there’s enough for hundreds of wheels!
Perhaps someone else in the club can make use of some :0)

 

[Roog]

I rebuilt the wheels for my tether car last week, I used new tires for the rear wheels but managed to reuse the front wheel tire. I used the strange two part rubber/metal glue to bond each tire in and tightened the wheel halves together, leaving it to set for a week.

So today was all about grinding the wheels properly round and smooth, can’t be too hard surely?

Now that the wheels are assembled I have to make a mandrel on which to mount the wheels this is fixed in the lathe chuck as though they are on the car drive shaft. It’s extra work, but I can’t think of an alternative to grind the tires concentric to the shaft and the wheel.

The dremel and grind stone are mounted to the tool post which allows quite precise movement and aim, I ran the lathe chuck in reverse with the dremel running at full speed. It took quite a while to face off each wheel to remove any eccentric moment of the tire face, taking about 2mm off the overall diameter.

A gentle sweeping motion of the spinning grind stone backwards and forwards across the face of the tire seemed to cut the best, leaving a nice finish.

Heavens to murgatroyd, what a mess

The rubber dust is really fine and mixes with the oil to make a gooey mess, everything thing I touch is covered with black smears.

On the positive I now have nicely smooth and round wheels

I just hope that these ‘bonded’ wheels hold together during the next outing to the track.

They need a clean, this rubber dust clings to every thing!

You can see from the ground finish that there are tiny bits of shiny stuff in the tire surface, this isn’t due to my grubby machining it is very fine metal wire (like heavy duty wire wool) embedded in the rubber conveyor belt mix, presumably for strength? When grinding I would get little bursts of orange sparks from time to time.

 

[Doom!]

Looks good! Will compressed air clean up the mess or make it worse? Sticky stuff can be a pain.

 

[Roog]

Looks good! Will compressed air clean up the mess or make it worse? Sticky stuff can be a pain.

Thanks @Doom! they certainly look much neater than the fresh sawn wheels, I can see now that I was a bit complacent thinking that wearing them in on the track would be OK.


I keep my machine tools coated in oil to minimise rusting, this means that machining is a messy affair at the best of times, I can’t afford to heat or dehumidify my shed I have to live with it. I am very jealous of YouTubers who work with spotless and dry machines although I guess they have to work hard to keep them like this( for the cameras.

The rubber dust just made things much worse, although copious squirts of WD 40 did help to wash most of it off.

The wheels on the other hand will brush clean, I’ll do that before I reassemble the car. I also need to remove the nail varnish markings which I put on the wheel hubs to make sure that I assembled the ‘matched’ parts as before, (they are supposed to all fit each other!)

On thing I noticed while grinding the surface of the wheel to a dimension is that the wheels expand due to the heat generated by the grind stone. So you measure when warm and later comparison showed that cooled finished wheels /tires shrank!

As long as you measure when warm they all seemed to end up the same size, although getting them round was probably the more important thing as putting a slightly larger diameter wheel on the outside of the track might be advantageous.

 

[Doom!]

Never thought of the tires shinking when they cooled. makes sense, just never occured to me.

 

[Roog]

Interesting and disappointing experience at the track today, with my bonded tires my car didn’t improve on its previous runs, there was a burning smell and vibration which brought the run to an end. Two of my tires held together absolutely fine, however one tried to escape its wheel/hub causing the uneven shape in the picture. Oh dear!

The glue remains well and truly bonded to the tire.

A bit despondent a club member offered me two ‘proper’ tires, I’ll have to replace them, this could be expensive.

I’m not sure how they are made, but they are quite solid, I think something has been moulded in its core.

So now I have to make some new hubs and probably a new drive shaft because the new tires are wider at the centre.

I’m finding this going around in circles really hard!

 

[Doom!]

Interesting and disappointing experience at the track today, with my bonded tires my car didn’t improve on its previous runs, there was a burning smell and vibration which brought the run to an end. Two of my tires held together absolutely fine, however one tried to escape its wheel/hub causing the uneven shape in the picture. Oh dear!

View attachment 187710

The glue remains well and truly bonded to the tire.

A bit despondent a club member offered me two ‘proper’ tires, I’ll have to replace them, this could be expensive.

View attachment 187711

I’m not sure how they are made, but they are quite solid, I think something has been moulded in its core.

So now I have to make some new hubs and probably a new drive shaft because the new tires are wider at the centre.

I’m finding this going around in circles really hard!

Sorry to hear about the tire, I thought you had it sorted out. Kind of a bummer but learn as you go.

 

[WickedFog]

Hopefully those new tires do the trick. I assume you have to machine new wheels to mount them?

 

[ahr43]

Speed racing is tough. Esp. tethered racing. Obviously placing loads on the car and chassis none of us 'straight liners' have experienced. Hard to make any recommendations.

Speed racing improvements, though, is usually measured with a micrometer, not a meter stick. Patience is paramount.

New tire assembly looks a beginning to a new plateau. Good luck. Cheers. -AC

 

[Roog]

Speed racing is tough. Esp. tethered racing. Obviously placing loads on the car and chassis none of us 'straight liners' have experienced. Hard to make any recommendations.

Speed racing improvements, though, is usually measured with a micrometer, not a meter stick. Patience is paramount.

New tire assembly looks a beginning to a new plateau. Good luck. Cheers. -AC

Thank you all, yes it’s a learning process with me starting from scratch. So hopefully the proper tires will let me get more than three or four laps in before I have to bail out.

We were talking about the influence of the tight circuit yesterday, as others have visited the circuit with their proven fast cars only to find that they lose 1/3 of that speed at this track. A larger diameter would be “straighter” and presumably faster and importantly to me, easier on the car.

As you say you try these things and learn, others with experience probably wouldn’t have tried to make tires out of conveyor belt off cuts! On a positive note the other two wheels held up very well.

Hopefully those new tires do the trick. I assume you have to machine new wheels to mount them?

Yes you are quite right it’s back to the drawing board and machinery to make a pair of hubs to grip these tires.
They have quite a small opening at the centre, from eye it looks like between 3/4” and 7/8” so my previous design might not be suitable, perhaps one big bolt through the centre will do? Certainly easier to make!

One other thing, a fella videoed each of the cars running yesterday, so when I get some footage I’ll post it via YouTube.

 

[WickedFog]

Thank you all, yes it’s a learning process with me starting from scratch. So hopefully the proper tires will let me get more than three or four laps in before I have to bail out.

We were talking about the influence of the tight circuit yesterday, as others have visited the circuit with their proven fast cars only to find that they lose 1/3 of that speed at this track. A larger diameter would be “straighter” and presumably faster and importantly to me, easier on the car.

As you say you try these things and learn, others with experience probably wouldn’t have tried to make tires out of conveyor belt off cuts! On a positive note the other two wheels held up very well.



Yes you are quite right it’s back to the drawing board and machinery to make a pair of hubs to grip these tires.
They have quite a small opening at the centre, from eye it looks like between 3/4” and 7/8” so my previous design might not be suitable, perhaps one big bolt through the centre will do? Certainly easier to make!

One other thing, a fella videoed each of the cars running yesterday, so when I get some footage I’ll post it via YouTube.

I would think a reverse cone shape for at least a couple centemeters around that center would be best to keep the tire from expanding.

 

[Roog]

Yup, I’ll have to get my protractor out

 

[WickedFog]

Yup, I’ll have to get my protractor out

Hey, look at it this way - they'll be fun parts to make. I always loved manual lathe work. Look forward to seeing what you come up with.

So what mph have you gotten it up to so far?