Hi, I'm Ro and I'm based in the New Forest

I've been wanting to build a kit car for years and years, but currently having 4 cars, none of which I can bear to part with, I thought I'd build something smaller.

I've always been interested in electric vehicles and when I saw the MEV Etrike I got hooked on the idea of a small electric reverse trike.

I've made a couple of changes to the design of the Etrike chassis and ended up with something that looks like this:





Main chassis tubing is 1 1/4 inch mild steel. I have acquired the front suspension off an old quad and the swingarm from a pitbike. The motor Is a Motenergy ME1003 which should produce 30hp peak. Batteries are located under the seat.

Obviously I still have to add the shocks and steering but any feedback at this stage would be appreciated!

Thanks for looking

ro

I love the idea - hats off for the leftfield approach. One question, why not make the roll hoop a single piece with a bend?

IIRC thekey to reverse trikes is to get the weight as far forward as possible so shove the batteries between the front wheels. There are a number of papers on the subject that should be available on Google
Cheers
Just remembered mark Ortiz and it was Aug 2015 newsletter
[Edited on 19-11-15 by v8kid]

[Edited on 19-11-15 by v8kid]

[Edited on 19-11-15 by v8kid]

The Motenergy ME1003 is 20Kw peak, 11.5max continuous at 72V

To run at that continuous power (which is probably way more than you need) you'd be pulling 140amps from your batteries - you're either going to need a lot more batteries than your pic shows (remember you'll need 6 x 12V to get to 72V before putting any in parallel to extend endurance) or you'd need to run at much lower power.

As already said the batteries need to be placed at the forward end towards/between the front wheels for stability, tho' with the weight that low should be reasonably stable anyway

I can't remember what Stig used for the Etrike, but don't think it was that powerful, a kart with two 6.5Hp engines, ie 13Hp can make speeds of over 70mph & 0 - 60 in around 5 secs I think, with 20Kw peak you'd have double that power in probably around double the weight so similar acceleration, but way higher top speed, it wouldn't maintain it for long at that power usage tho'

Wow, thanks for the responses!

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Originally posted by twybrow
I love the idea - hats off for the leftfield approach. One question, why not make the roll hoop a single piece with a bend?

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Originally posted by v8kid
IIRC thekey to reverse trikes is to get the weight as far forward as possible so shove the batteries between the front wheels. There are a number of papers on the subject that should be available on Google

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Originally posted by russbost
As already said the batteries need to be placed at the forward end towards/between the front wheels for stability, tho' with the weight that low should be reasonably stable anyway

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Originally posted by russbost
To run at that continuous power (which is probably way more than you need) you'd be pulling 140amps from your batteries - you're either going to need a lot more batteries than your pic shows (remember you'll need 6 x 12V to get to 72V before putting any in parallel to extend endurance) or you'd need to run at much lower power.

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Originally posted by russbost
I can't remember what Stig used for the Etrike, but don't think it was that powerful, a kart with two 6.5Hp engines, ie 13Hp can make speeds of over 70mph & 0 - 60 in around 5 secs I think, with 20Kw peak you'd have double that power in probably around double the weight so similar acceleration, but way higher top speed, it wouldn't maintain it for long at that power usage tho'

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I learned the hard way. A trike chassis needs to be stiff in torsion. Put a good X brace in the floor of the chassis.

You want the weight as low as possible. Don't put the batteries under the seat. Fit the seat as low as you can.

You also want the weight to be towards the front. If you want to do the calcs, this is what you want to aim for. Take the worst case scenario - the car going down a 1 in 3 hill with the brakes stopping you at 1.5g with the rear wheel going over a bump. Draw a line from the centre of gravity that is the sum of gravity and deceleration and the bump force. It MUST touch the ground behind the line of the front axle. Not difficult to calculate but quite involved.

In short, put the heavy stuff at the front.

At at steady urban speeds, you might draw 6kW from the batteries - around 80A. On a dual carriageway, you might pull 30kW out of the batteries - well over 400A. You'll need a really thick cable!

[Edited on 19-11-2015 by smart51]

"OK, I naively assumed that more weight near the rear wheel would improve traction, but after a good google of the subject I can see you both are correct. Can you see any problems with putting the batteries forward of the front axle line, or do they have to go directly between/just behing the axle line?"

If you put the batteries forward of the front axle line you could easily finish up standing it on its nose under braking you need to do the calcs Smart51 suggests

"I was planning to use 6 YC33 batteries in series to give me 72V.
I'm hoping that most of the time I would not be drawing anywhere near 140 amps, only occasionally using higher powers for spurts of acceleration. Would these batteries be able to deliver short bursts of 140amps?"

They don't seem to give a max current spec, but I would think 140A would be no problem for short bursts, but @35Ah those batteries as a pack of 6 aren't going to last long or get you very far - downhill & on the flat is no problem, but put a few decent uphill stretches in the way where you might be pulling 200A or more & you'll be coming to a grinding halt fairly rapidly, also remember that even with traction batteries they recommend that you don't regularly discharge below 50% so that 35Ah just became 17Ah!!

" I was hoping that the ME1003 would be a decent replacement. Do you think it's overkill and I should really be looking at something smaller like the ME0708, or should I just find somewhere to stash more batteries and go for it?"

Depends entirely what you are trying to achieve & what you want the trike to do, if you want dragster like acceleration then you want the biggest motor you can get, if you want endurance the smallest etc etc If it's for a regular commute or regular local journeys where you can top up the batteries regularly then you have a whole different ball game to if you're planning on taking it on a touring holiday! I would have thought for a lightweight vehicle the ME0708 would be adequate, remember that electric motors have all their torque available pretty much all the time, not just at a certain rev band. Re stashing more batteries, a lot depends on your budget!

I would suggest join batteryvehiclesociety.org.uk & have a chat with the guys over there, they are the gurus for this sort of stuff, I have only dabbled & have my basic A level physics & HND in engineering for info, but most of it is common sense, you just need to do a few sums to check what's feasible

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Originally posted by russbost
If you put the batteries forward of the front axle line you could easily finish up standing it on its nose under braking you need to do the calcs Smart51 suggests

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Thanks for all the feedback. I'm reworking the design to try to take it all into account, but it's taking a while. I'll post the changes as soon as I have them.

On the motor front, would it be worth going for a 48v system and 8 x 12v batteries instead of 72v with 6? Or will the larger current draw empty the batteries sooner?

Thanks again to everyone for the help!

"On the motor front, would it be worth going for a 48v system and 8 x 12v batteries instead of 72v with 6? Or will the larger current draw empty the batteries sooner?"

It will depend on the overall current draw of the motor vs the storage capacity of the batteries, as a very rough general rule if you're using a lower power motor (ignore voltage, look at Kw or HP) & more batteries of similar capacity you're going to have less performance & more range

Right, Ive made some changes to the design based on the help you guys have given me (Thanks!)

The motor has been changed to a LEM170 allowing me to have 2 banks of 4 batteries (and the capacity to add 2 more banks if I need to) which should give me about 1/2 an hour run time.

The batteries have been moved over the front wheels to move the centre of gravity forward, and with my bulk towards the rear I don't think there's much chance of it standing on its nose!

The lowering of the seat has allowed me to lower the roll hoop and I've changed it to a single radius to match the front. Oh, and I've added some X bracing to the floor.

What do you think?

I guess you are going to use a toothed belt or chain drive direct to the rear wheel without a gearbox?

In which case you can offset the motor and have the motor spindle co-axially aligned with the swinging arm front bearing that way the belt/chain tension will be constant rather than slacking under acceleration.

Handily that will free up some space on the side opposed to the motor and you could install a small 2 stroke 800W generator constantly charging the batteries. As battery capacity (in Ahr) increases as the discharge current (A) gets less you get a double whammy of either increased range or power for the same range.

I would have some sort of bulkhead between the batteries and my body. Acid burns!

An alternative is to have two motors one driving each front wheel as the characteristics of electric motors gives an automatic differential effect.

Not sure why you want to reduce the voltage! Higher voltages are more efficient and the control gear is lighter and cheaper due to the lower currents. If its down to the size of batteries available remember as you double the voltage you halve the Ahr capacity required.

Cheers!

Along with that roll hoop, I would perhaps have another look at the top wishbone mounts too, look like a little leverage would have them ripped off the tube with the length of them?
Looking good tho

Fwd is the way forward on safe handling trikes....

some interesting ideas here.
but what motor controller might you use?
ok I haven't built any electric cars (yet), but I thought if you used a pwm controller (pulse width modulation) you can / should feed it with a higher voltage than the apparent output voltage.
so could you not use the "Motenergy ME1003" and 8 12v batteries (~96v) and feed them into a controller like this:
200A 24-100V 24V 48V 60V 72V current limited DC motor PWM speed controller
eBay Item

ps that power controller seems to accept sister units to double its capacity too.

[Edited on 21/11/15 by gremlin1234]

Gotta agree with Volvorsport on FWD being the better way for safe handling on a trike, though there are plenty of RWD trikes out there with much higher power:weight ratios than you'll have, and they do just fine when driven sensibly.

These threads on Martinslyon's similar electric trike project might be of interest:
http://www.locostbuilders.co.uk/forum/27/viewthread.php?tid=172100&page=1
http://www.pistonheads.com/gassing/topic.asp?h=0&t=969988&d=11985.23157&nmt=

I don't know how far he got with it - it seemed to go quiet - but notwithstanding a few caveats about battery location and monoshock design, it seemed like a promising idea.

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Originally posted by v8kid
I guess you are going to use a toothed belt or chain drive direct to the rear wheel without a gearbox? In which case you can offset the motor and have the motor spindle co-axially aligned with the swinging arm front bearing that way the belt/chain tension will be constant rather than slacking under acceleration.

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Originally posted by v8kid
Handily that will free up some space on the side opposed to the motor and you could install a small 2 stroke 800W generator constantly charging the batteries.

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Originally posted by v8kid
I would have some sort of bulkhead between the batteries and my body. Acid burns!

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Originally posted by blakep82
Along with that roll hoop, I would perhaps have another look at the top wishbone mounts too, look like a little leverage would have them ripped off the tube with the length of them? Looking good tho

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Originally posted by gremlin1234
...but I thought if you used a pwm controller (pulse width modulation) you can / should feed it with a higher voltage than the apparent output voltage.
so could you not use the "Motenergy ME1003" and 8 12v batteries (~96v) and feed them into a controller

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Lots of people have tried and never really succeeded so you can't look to tried methods - after all its pointless copying failure!

The issue is the weight and limited capacity of the batteries. So why not dump the big batteries?

Super capacitors are light with very good discharge rates but do not hold a huge charge. They would do for acceleration power but run out of steam for cruising. Add a lightweight generator for cruising.

There may be a balance to be met between the size of generator and the cruising speed in which case you could have a smaller generator coupled with motorcycle batteries which gives a higher cruising speed.

The project could be completed in stages with a bit of smart planning at the beginning.

Could be a long project though 😁

Cheers!

If you're concerned about weight and range, a generator is the way to go. An ordinary car might have 100 BHP but you hardly ever use it all. You might use half of that during brisk but sensible acceleration and about a fifth of that on a level motorway. The best thing to do is have 100 BHP electric motors and enough battery to supply this for say 15 minutes. Then have a 25 BHP generator supplying the electricity

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Originally posted by smart51
If you're concerned about weight and range, a generator is the way to go. An ordinary car might have 100 BHP but you hardly ever use it all. You might use half of that during brisk but sensible acceleration and about a fifth of that on a level motorway. The best thing to do is have 100 BHP electric motors and enough battery to supply this for say 15 minutes. Then have a 25 BHP generator supplying the electricity

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The opposite extreme of the balance is to do what Honda has done with its IMA system; use the IC engine as the prime mover, with an electric motor to provide the 'boost'.

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Originally posted by v8kid
If the project can minimize the weight it would be a great fun machine to play with - after all the OP is not trying to produce a viable alternative to a mass market tin top - at least I presume not

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Is there not a battery pack that comes from a hybrid that you can use already?

Interesting project.

Keeping it simple must be the way forward.

I guess getting an affordable drive train (motor batteries) is the main challenge.

http://www.evalbum.com/ is a good site to get some ideas.

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Originally posted by Sam_68

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Originally posted by smart51
If you're concerned about weight and range, a generator is the way to go. An ordinary car might have 100 BHP but you hardly ever use it all. You might use half of that during brisk but sensible acceleration and about a fifth of that on a level motorway. The best thing to do is have 100 BHP electric motors and enough battery to supply this for say 15 minutes. Then have a 25 BHP generator supplying the electricity

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With range extender hybrids, though, it's a difficult and complicated balancing act to get right in terms of efficiency.

If you're not careful, after the first 15 minutes you effectively end up with a 25bhp IC-engined car, but with its efficiency reduced by 30% for all the losses incurred converting the IC engine's horsepower to electricity (generator), then to chemical energy (batteries), then back to electrical energy (batteries), then to horsepower that can be used at the wheels (electric motor).

That's an over-simplification, I know - ignoring factors such as being able to run the IC engine at constant revs and load, optimised for efficiency - but still not far off reality.

The opposite extreme of the balance is to do what Honda has done with its IMA system; use the IC engine as the prime mover, with an electric motor to provide the 'boost'.

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Originally posted by smart51
In my example the engine will be on most of the time. The battery will supply the extra power for acceleration and hill climbing, with the surplus power from the generator charging the battery the rest of the time.

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Originally posted by Sam_68

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Originally posted by smart51
In my example the engine will be on most of the time. The battery will supply the extra power for acceleration and hill climbing, with the surplus power from the generator charging the battery the rest of the time.

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Then you'd probably be better off with the IC engine driving the wheels directly, with the electric motor to assist it (Integrated Motor Assist - the Honda approach), rather than acting as a generator.

Every time you force energy to change form there is a percentage loss in efficiency, so it doesn't usually make sense to make your primary source of power change its form many times on its way to the wheels (chemical>heat>mechanical>electrical>chemical>electrical>mechanical in your example).

That's why operating regime is so crucial to how effective different forms of hybrids are: Range Extender PHEVs are at their best when most of their journeys are short enough to be pure electric (city or local driving), whereas IMA works best on longer/faster motorway and open road driving.

Get the balance wrong, and one half of your hybrid powertrain is little more than dead weight.

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OK, after trying lots of designs, I have given up on the idea of widening the body and putting the batteries down the side. I just could not make it look any good

I think I've now virtually nailed the design. 6x55ah batteries up front. Wishbones and steering reversed to make extra room for the batteries. Seat canted to allow a "legs bent" driving position gives me more room at the front.




I've also moved the floor above the cross braces and slightly increased the length of the rear section to allow more access to the motor.



Unfortunately I could not find a way of mounting the motor co-axially with the swingarm without drastically increasing the width of the whole trike

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Originally posted by Volvorsport
Is there not a battery pack that comes from a hybrid that you can use already?

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Originally posted by ettore bugattiI guess getting an affordable drive train (motor batteries) is the main challenge.

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Originally posted by blakep82
Along with that roll hoop, I would perhaps have another look at the top wishbone mounts too, look like a little leverage would have them ripped off the tube with the length of them?

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I've found a certain French small car manufacturer has a subframe where all the bits happily Bolt on

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Unfortunately I could not find a way of mounting the motor co-axially with the swingarm without drastically increasing the width of the whole trike

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Originally posted by smart51
How about mounting the motor on the rear swing arm...

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Originally posted by Volvorsport
I've found a certain French small car manufacturer has a subframe where all the bits happily Bolt on

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