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18 October 2020, 08:49:29 pm

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Re: Delage 15-S-8 by Adrian
18 October 2020, 02:14:50 pm

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Author Topic: Delage 15-S-8  (Read 43819 times)


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Re: Delage 15-S-8
« Reply #165 on: 18 October 2020, 02:14:50 pm »
The project is looking very nice indeed Marek. Cool car to start with.
I know you and your Dad have done much work on the electric 'theory' behind the design and you have certainly found a nice gearbox to use.  Could you fill me in with the ideas behind using a gearbox. I thought that an electric motor would drive the axle directly.
Maximum torque for an electric motor occurs at stall and the voltage applied will determine its rpm (in the case of a brushless motor very precisely). The motor and speed controller must be capable of dealing with the resulting Amp load of course. Even off-the-road electric motorcycles manage without one.
I think it's on the USA Cyclekart site where a guy has built a few of them and an early one had a gearbox but it got ditched for the subsequent ones.

Here there is a company called 4QD (https://www.4qd.co.uk) that make speed controllers that would suit this application very well and I recommend you give them a call because they are very helpful and can advise on all aspects (Motors, batteries, speed-controllers) for such a project.

My understanding is that as long as the battery is able to deliver the voltage you need at the Amps being pulled then no gearbox is necessary and you will be 'off-the-line like lightening and top speed should be more than adequate.

I really would like to know because I am thinking about building an electric one also.


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Re: Delage 15-S-8
« Reply #166 on: 18 October 2020, 08:49:29 pm »
The gearbox is a single speed. 7.5:1 ratio planetary gearbox. this is doing the same thing as chain sprocket gear ratios, I just dont have enough room for a big enough sprocket to do this with sprockets so most of the ratio is taken out with the gearbox (note there is no clutch so we are using that immediate torque) and then some small sprockets finish off the ratio. I did the calculations to work out the torque needed for my target acceleration so I should outpace people out of the corners and off the line but some of the faster CKs will easily have me on the long straights. One of the other benefits of having only a small sprocket ratio is that because ratios in line multiply. I can get a couple of relatively cheap sprockets for the back axle that I can swap out depending on situation (eg. corona 30 second speed challenge or brooklands test hill would need different ratios to get the best time or top speed out of the kart). In the First drivetrain video (the only one out at the moment) I explain the ratios and what the total ratio is. I have estimated the weight of the CK as being similar to Dad's Bugatti plus a bit more for battery weight but when the kart is almost done I can have a go over and see where I can take out some weight or if there is anything I can do to reduce the weight which means I can then modify those chain ratios to get the best top speed out of my desired acceleration. I am using the Golden Motors 3KW 48V motor as this is what has been used in the states and seems to come out with similar performance to GX200 karts. As this is the lower voltage it will naturally be less efficient than its higher voltage counterpart but 48V will be much much safer and means that if I did manage to get shocked then I should be okay (I will be making sure everything is safe and will obviously not planning on getting an electric shock) but 50V is about the voltage it takes to break through dry skin so the risk of major damage to anyone is lower.


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Re: Delage 15-S-8
« Reply #167 on: 19 October 2020, 07:45:16 am »
Marek has pretty much covered it, but a couple of extra observations/assumptions.

Whilst electric can give you high torque, it’s not infinite.  The motor Marek has, peaks at about 20Nm compared to a GX200’s 13Nm.    Of course, given how bogged down our engines get when coming out of corners, it’s questionable how often we achieve peak torque from the gassers - the electric motor should perform better in these circumstances.

The current drawn ramps up very quickly for peak torque, so Marek’s motor draws 100A for 20Nm.   Our research so far says that the safe peak current for the batteries we can get is about 2C - ie twice the capacity of the battery. So, for 100A, Marek will need 50Ah batteries.    This is starting to create another design constraint, because 48V, 50Ah batteries will add significant weight and size, not to mention cost.

One aspect of this is to apply engineering principles and then compare them to real life performance.   It’s not as direct a route as copying what someone else has done, but it’s potentially a much richer learning route.   All part of the fun!