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Old 06-19-2012, 02:09 AM   #76
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Originally Posted by iamahuman View Post
Good to see you're beating CF'ed out cars with your fibreglass chassis. Goes to show that design is a big aspect of racing.

Will you be moving to CF? Any advantages of that (over the fibreglass chassis) other than flex characteristics?
Yes the final chassis will be CF, just using fibreglass for now as it's much easier to cut and drill (and it's cheap!).

CF should be lighter for a given stiffness, although the car needs 30g of weight to get to the 1350g minimum anyway, so I doubt this will be worth much laptime.

Main benefit is that it looks pretty
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Old 06-21-2012, 02:53 AM   #77
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Race summary #3

Another dry evening at Bedworth in the UK, and another successful outing for the prototype car.

My runs tonight were

19/306 (crashed + old tyres)
20/315
20/314
20/313 (would have been 20/311 if this was a qualifier - lost 2s on first lap due to grid start).

So that's 3 new PBs in one evening. The car is now 3s faster than the TC6 over a run, and 0.15s faster on fastest lap, with still plenty more to come.

Things tested

For the third heat I tried a more flexible topdeck (the centre section was narrowed by 3mm, and the prongs by 2mm). This didn't seem to have a major effect on the cornering, but it did seem to help over the bumps, which is one of the cars current weak points. I have tried running softer springs which also helps over the bumps, but takes the edge off the cornering. So a flexible chassis and stiffer springs seems like a better direction to go. I'll make another topdeck for next week with even more flex to see how this goes; I also want to even up the flex as at the moment most of it happens at the rear.

For the final I tried moving the front shocks to the inner hole on the wishbones, and going up one rate on the front springs (Silver to Pink). This makes the front end a lot softer overall, and is something I've wanted to try for a while. The effect was quite dramatic; I had a lot more steering everywhere, especially mid-to-exit and at high speed. But the rear was still planted making for a fast, stable car. I think there's a lot more time to come with this setup once I adjust to all the extra front end and make use of it (I was on the grass on the inside of a few corners it had so much grip).

I also tried a rear belt tensioner as a quick fix to stop the rear belt slipping. It helped a bit but didn't totally cure the issue. I think the rear layshaft and diff may be moving towards each other under acceleration and braking (pulled together by the belt), so I'm going to add a carbon brace to prevent this. It will just butt up against the rear bulkhead without bolting to it, so the main side-to-side chassis flex will be unchanged.

The Tornado fan on 6v also survived the evening. It was a warm evening and even running at a faster pace (and doing an extra lap) the motor was still under 90deg so temperatures are well under control.

That's all for now, thanks for reading
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Old 06-21-2012, 03:02 AM   #78
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Sounds really good Dale, congratulations!

Are you still using the non RC belt on the rear? Maybe its extra thickness isn't allowing it to wrap around the pulley as nicely as a thinner RC belt? The offer of that Scythe belt is still there if you need it...

Looking forward to seeing the car in CF as well, that will gain you a couple of tenths a lap in looks alone

Whats your email address mate, would like to send you a couple of pics of my proto to see what you think. Been out tetsing with it lately and its been good, first real test at the STCC at Ipswich this weekend...if it stops raining!
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Old 06-21-2012, 03:11 AM   #79
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Hi Dale. Very interesting project and it's been a great read so far. Congrats it's coming together so well. I do have one question. What does your car weight ready to run?
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Old 06-22-2012, 02:11 AM   #80
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Originally Posted by Chrissy C View Post
Sounds really good Dale, congratulations!

Are you still using the non RC belt on the rear? Maybe its extra thickness isn't allowing it to wrap around the pulley as nicely as a thinner RC belt? The offer of that Scythe belt is still there if you need it...

Looking forward to seeing the car in CF as well, that will gain you a couple of tenths a lap in looks alone

Whats your email address mate, would like to send you a couple of pics of my proto to see what you think. Been out tetsing with it lately and its been good, first real test at the STCC at Ipswich this weekend...if it stops raining!
Had a close look at it last night, testing it like I'd test for rear ball-diff slip. I can now clearly see that the rear layshaft and diff are being pulled towards each other by the belt, causing the belt to slip. Should be a very easy fix, just needs a small carbon block bolting to the top of the layshaft mount to keep the bulkhead from being pulled into it.

I've PM'd you my email address.

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Hi Dale. Very interesting project and it's been a great read so far. Congrats it's coming together so well. I do have one question. What does your car weight ready to run?
It weighs 1355g (with 30g of lead). The carbon chassis and some titanium screws should allow a bit more ballast to be added which can then be moved forwards or backwards for tuning.
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Old 07-10-2012, 03:54 AM   #81
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Time for a little update since it's been a while. The prototype is still running well and is now my regular race car; I haven't raced the standard TC6 since I started racing the prototype.

The car had it's first major(ish) outing at the weekend, at the BRCA Clubmans round at Bedworth. I qualified 6th overall against a very competitive field, setting a new PB in the process, so a great result. The finals didn't go well with a motor issue and a broken servo arm due to being hit by another car, but thats racing.

I did briefly try the TC6 during Saturday practice, as I wanted to retest a full-fat 6000 60C lipo against a shorty. Once again this confirmed that the speed and drop-off is identical, so there is zero advantage of the bigger packs in 13.5 boosted.

This also reminded me just how different the prototype handles compared to the standard car. I couldn't believe how much understeer I had with the TC6 (on an identical setup). Even some large setup changes couldn't make it have the positive feeling the prototype has through the corners.

I've just purchased a dial-gauge and stand so that I can measure chassis flex, and measure the stiffness of different composites (i.e. carbon vs GRP). This will give me an indication of how thick I need to make the carbon chassis, and wether it might need extra cutouts or a different top-deck to get the same flex as the GRP chassis I'm running at the moment. I'll probably start on the stiff side and remove material if needed, since thats better than trying to add stiffness back in with braces etc.
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Old 07-10-2012, 08:11 AM   #82
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if this was ever a kit to be produced I think it would be an awesome product for racers to choose from. great job and keep up the hard work!
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Old 07-13-2012, 03:27 AM   #83
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I spent a couple of hours yesterday evening testing the stiffness of different materials. For this I cut some identical sized strips from various different materials, bolted each one to a heavy block of metal, and used a dial gauge to measure how much each one flexes when weight is applied.

The results are:

2.0mm GRP - 0.32mm flex
2.4mm GRP - 0.16mm flex (current chassis)

2.0mm CF - 0.24mm flex
3.0mm CF - 0.06mm flex

Both GRP and CF seem to obey the expected laws, which is a cubic relationship between thickness and flex (i.e. a small increase in thickness gives a massive increase in stiffness).

I'm planning to use 2.4mm CF for the final chassis, which should have a flex of 0.12mm, so a fair bit stiffer than the GRP I'm using at the moment. This should actually be beneficial; I need extra stiffness in a couple of areas (around the layshaft and motor mounts) to stop the mounts flexing under the strain of the belts. I'll then add some cutouts to give the same flex as the current chassis, to keep the handling similar.

One final thing I need to do is weigh the test pieces, so I can see how much weight saving I'll get from the CF chassis.
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Old 07-16-2012, 03:19 AM   #84
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hi!

Can you share weight in grams per 1cm2 (1cm x 1cm) of this materials?

Thank you
m.

ps: I found that my GRP 2.3mm is 2.55g/1cm2, and 3.11mm is 1.77g/1cm2
(checked 2x times), need to compare with carbon, and I see you can help me
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Old 07-16-2012, 04:29 AM   #85
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I have now weighed the test pieces. For some reason my results differ to yours for GRP but anyway here they are:

2.0mm GRP - 0.39g/cm2
2.4mm GRP - 0.50g/cm2
2.0mm CF - 0.28g/cm2
3.0mm CF - 0.50g/cm2

So changing from a GRP to a CF chassis and topdeck should save me around 30g, although this will have to be added back as ballast, so I'm not sure there's a huge benefit as far as weight goes. The ballast will be a more centralised, although it will also be slightly higher than the chassis. The main benefit will be increased stiffness in certain important areas.
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Old 07-16-2012, 05:00 AM   #86
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hm .. I have my notes:

30.5x20.4 cm = 662.2 cm2 = 266g => 265/662.2 = 0.4g/cm2

50.8 x 25.6 = 1300.48 cm2 = 734g => 734/1300 = 0.56g/cm2


my mistake !!!!
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Old 07-16-2012, 06:00 AM   #87
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Quote:
Originally Posted by daleburr View Post
I spent a couple of hours yesterday evening testing the stiffness of different materials. For this I cut some identical sized strips from various different materials, bolted each one to a heavy block of metal, and used a dial gauge to measure how much each one flexes when weight is applied.

The results are:

2.0mm GRP - 0.32mm flex
2.4mm GRP - 0.16mm flex (current chassis)

2.0mm CF - 0.24mm flex
3.0mm CF - 0.06mm flex

Both GRP and CF seem to obey the expected laws, which is a cubic relationship between thickness and flex (i.e. a small increase in thickness gives a massive increase in stiffness).

I'm planning to use 2.4mm CF for the final chassis, which should have a flex of 0.12mm, so a fair bit stiffer than the GRP I'm using at the moment. This should actually be beneficial; I need extra stiffness in a couple of areas (around the layshaft and motor mounts) to stop the mounts flexing under the strain of the belts. I'll then add some cutouts to give the same flex as the current chassis, to keep the handling similar.

One final thing I need to do is weigh the test pieces, so I can see how much weight saving I'll get from the CF chassis.
Dale,

One thing to point out, is you've made the fundamental assumption that carbon and GRP materials behave the same way as traditional isotropic materials (steel, alu etc). With composites, one of the biggest differentiators is simply the lay up used and the resulting direction of the fibres.
Most chassis plates you see on the market are not actually what they appear, mostly a cover of woven (the good looking stuff), with UD fibres beneath specifically orientated to tune the flex.
Put it another way... If you have a sheet of material laid up with mostly UD along the length, and then cut a chassis at 90deg to the fibre, it would behave wildly different to one cut at 0deg to the fibre.
Combine that with the shaping and cut-outs in the chassis... and theirs your chassis flex black magic
Something to think about anyway

Regards
Ed
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Old 07-16-2012, 08:00 AM   #88
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Dale,

One thing to point out, is you've made the fundamental assumption that carbon and GRP materials behave the same way as traditional isotropic materials (steel, alu etc). With composites, one of the biggest differentiators is simply the lay up used and the resulting direction of the fibres.
Most chassis plates you see on the market are not actually what they appear, mostly a cover of woven (the good looking stuff), with UD fibres beneath specifically orientated to tune the flex.
Put it another way... If you have a sheet of material laid up with mostly UD along the length, and then cut a chassis at 90deg to the fibre, it would behave wildly different to one cut at 0deg to the fibre.
Combine that with the shaping and cut-outs in the chassis... and theirs your chassis flex black magic
Something to think about anyway

Regards
Ed
At this stage I'm not too concerned with what the manufacturers are doing with their carbon; as you say it's impossible to know whats under the surface. Even if I did, I don't think anyone's going to make me a one-off chassis with a special carbon layup for any amount I can afford

I'm largely doing my own thing as far as flex goes; my current GRP car has evolved with a bit of trial and error to get it to an amount of flex that seems to work well in most conditions. I then have a couple of different top-decks I can use to add or remove flex.

My material flex tests were performed on the GRP I'm using on my current car, and the type of carbon I'll use for the final chassis, so it should tell me what to expect when I go from GRP to carbon. Although a bit more trial and error may still be needed, by adding some more cutouts or altering the top-deck again.
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Old 07-19-2012, 03:07 AM   #89
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Race report

Another dry evening of racing at Bedworth yesterday. Despite it seeming to rain all the time in the UK this year, we've actually got a lot of dry racing in (it helps that this track dries very quickly). Think I've only done about 4 runs with the wet car all year.

Another new 13.5T PB for the prototype of 20/310, this now equals my best 10.5T time from last year, and is a full 6 seconds quicker than I've been with a standard TC6. In the final I was happily running on the tail of the current lap-record holder until I grip-rolled (very strange, I suspect the bodyshell caught a tyre), so a great evening overall.

The car continues to get a lot of attention, with a few people asking if I'm going to make a conversion kit available. Sadly not at this stage, as I just don't have the time. Although I'd love to retire and spend my days playing with toy cars, I don't think it pays very well...

The only changes for this run were a new middle belt (at a cost of 1!) which got rid of all the belt slip the car had developed, and some small changes to the Hobbywing ESC settings to reduce the motor temperature further. This reduced the dropoff at the end of the run, and didn't seem to harm the speed at all. The motor is now running at just 70deg which is super-cool for an X12. Although the X12 will run to 120deg, it certainly seems to perform better at lower temperatures, which is no surprise really.

We have another race at the weekend, and it looks like its going to be dry and sunny both days, so a full weekend at the track is in order to try some more car setup and ESC changes to squeeze a bit more performance out of it.

Interesting links

Some other prototypes for your perusal...

http://ets.redrc.net/image-gallery-1...rd1/?nggpage=4

http://rc-car-driver.de/showthread.php?t=15197&page=16
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Old 07-19-2012, 03:07 AM   #90
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Last edited by daleburr; 07-19-2012 at 03:08 AM. Reason: Duplicate post
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