Scratch build electric tethered car racer

[Roog]

Posted on this very fine forum because I was an RC modeller many years ago a this model will have an RC throttle control! (no steering required.)

Why am I doing this? Well because I want to see how fast it will go and because I was told by the local club that electrics are the ‘work of the devil‘ and that only IC power is for real cars. I am going to prove them wrong.

The informal speed record at the small local club circuit is a modest 50mph or so held by a 1.5cc air screw powered car, this situation cannot remain, imho ’cars’ should be driven by power through the wheels!

I have a plan, more of that later, but for now the parts have started to arrive.

and I have a selection of tooth belt pulleys which should give me the option of 2:1 or 2.5:1 ratios over 3M or 5M 15mm wide belts. I have yet to see how durable the finer belts will be?

 

[TRAT]

Hmmm I think I have a slot drag car that was proven in the 60s super fast but on Nitro.

Hmmm I think I have a slot drag car that was proven in the 60s super fast but on Nitro.

I’ll keep eye on this build for sure

 

[Greywolf74]

can't wait to see it take shape

 

[Roog]

I’ll try not to disappoint

you will have to be patient though because last time I made wheels they took an age and are very boring to do. On a three wheeler such as this car you have to make 6 wheel halves which are very similar.

 

[bill_delong]

the world record was set by an all electric car:
https://www.rccaraction.com/202mph-12-cells-inside-worlds-fastest-rc-car/

 

[Roog]

the world record was set by an all electric car:
https://www.rccaraction.com/202mph-12-cells-inside-worlds-fastest-rc-car/

Wow that is impressive, I cannot contemplate running an RC car at high speeds let alone 202mph. I am interested to see that it has gear and belt drive Systems

It is quite an interesting comparison because the challenge of stability and steering of an RC car compared to a tethered car where direction is dictated by the wire tether, and therefore not a thing you have to think about much during the run is off set by the extra air resistance of the tether wire its self which the RC car does not have.

I like that car body design. Most fast tethered cars look like 'spear heads'

I do have one significance challenge and that is the diameter of our local track, which makes very fast speeds a safety concern, hence i have set the gearing of mine to around 120 to 130 mph and given that I have not seen a car go faster than 50mph on our track should be quite exciting enough!

Let us see.

A bunch of pulleys and toothed belt (3M HTD one missing), offering a couple of gear ratio options arrived last week, I am looking forward to setting out the motor and drive axles on paper, i'll probably start with 2:1 and see if the motor has sufficient torque to get away.

I also have some bevel gears, but they might be for a future build.

 

[Roog]

The plans for my car are in need of developing, here is the current Plan and elevations

but I have been getting on with the wheels, first, cut some tires.

cut from 10mm thick conveyor belt rubber, I need three for my new car but thought I might as well cut the rest from the sheet. So I have a couple of spares.

The wheels are currently in their raw freshly cut state. Once mounted on their wheel, I plan to grind them to their final diameter. The other element I can get on with are the wheels, I hate making wheels, it’s only a three wheeler but that still means I have to make six halves, here is the first one.

face off and cut it down to the final diameter, which is 63mm for my 80mm diameter wheels

Next mark off the three wheel bolt centres, in the past I have done this at the end but found the results variable so this time I am trying to drill the tap size holes early on. Three bolts hold the two halves of the wheel together, bit like the wheel bolts on a Citroen 2CV!

drill M4 tap holes for both halves of first wheel.

 

[Roog]

Next back in the lathe to machine the tire hub

the narrow raised lip 0.5mm deep at the outer edge is meant to hold the tire firmly like a clincher rim, well that’s what I tell myself anyway.

next parting off, I hate parting off and usually end up sawing the thing off in a vice!

first half rim cut off the main lump of metal stock it’s back in the lathe to face off the outside face of the wheel

little chamfer to tidy up the outer edge and on to centre drilling the main hole for the drive shaft. Plan is to ream it to a precise 8mm then machine the 10mm drive shaft down to 8 mm to fit the wheels.

 

[TRAT]

I like this!!

 

[Roog]

Thank you @TRAT looking at the photos I posted yesterday evening I realise a couple of mistakes I made and how rough my machining is, the next one will be better. LOL!

I should have mentioned, the finished wheels are meant to look a bit like these which I made for a previous model, latest ones should be a little lighter, I hope.

 

[Greywolf74]

Good stuff!

 

[Roog]

I’ve made some Christmas decorations too!

 

[Roog]

Making the recesses in the three wheel bolts, drilled first then finish with an end mill

next drill the centre hole for the drive shaft just less than finished diameter them use a reaming tool to take it to final size.

I’ll not bore you with me building the other half of the wheel but here’s me truing the bar stock to start machining the other half. Trick is to rotate the metal in the chuck find find the high spot, then tap that down with a soft faced hammer, keep doing this until the dial stays put.

and here is the back of the finished other half, what you can see here is the start of the groove to accept the drive pin. this was taking too long as the cut depth was very limited, 0.1mm per hand wound sweep, so I stopped here and need to find a better way. Lots of 2.5mm holes in a row perhaps?

 

[Roog]

Oh dear, I’ve just noticed that the cable from the digital readout sensor is in a bad way. Still works but clearly in need of repair.

 

[Greywolf74]

Dont get any of those Christmas decorations stuck in your fingers lol

 

[Roog]

Took a break from making wheels, fixed the wiring to my lathe Digital readout and did the scariest operation so far, programme and run my motor / speed controller combo.

Thank you to the YouTube video posters who helped me with the use of the program card, easy once you know how.

 

[Greywolf74]

Gonna run it on 6S, I'm assuming?

 

[Roog]

Gonna run it on 6S, I'm assuming?

4S I’m a chicken (UK expression for coward!)

but if the car proves to be stable perhaps I could upgrade to 6S <evil cackling laugh>

My 2.5mm diameter end mill arrived, it looks very fragile, so I bought two, perhaps that should have been five! Oh well here goes:

Took it very slowly drilling lots of holes in a row then running through to create a 2.9mm deep slot across the back of the inside hub in which the drive pin engages. It seems that one end mill was enough, it survived the ordeal.

so now I have two wheels, one shows the front, the other the rear with the drive slot.

just one more to build, good grief!

 

[Greywolf74]

4S I’m a chicken (UK expression for coward!)

Its the same in the U.S. too

Looks like you're making progress

 

[Roog]

Its the same in the U.S. too

Looks like you're making progress

that’s a comfort :0)

Early on in my career I worked with a client in the US and as I got to know them more I found my self lapsing into using slang words and quickly realised that there were words used in the UK that didn’t transfer well to my US counterparts, nothing embarrassing or rude most simply led to mild confusion.

hopefully it will get more interesting soon