# RPM controller advice for "buggy"



## floydr (Jun 21, 2021)

Search on ebay or amazon for DC10-50V 12V 24V 36V 48V 50V 100A Reversible PWM Motor Speed Controller +Pedal or DC 10-55V MAX 60A PWM Motor Speed Controller CW CCW Reversible 12V 24V 36V and adapt a pedal throttle to it. You can add batteries as he gets older.
later floyd


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## GijsB (10 mo ago)

Thank you Floyd! I tried this controller:








Pwm motor regelaar 10-55V 100A met omkeer schakelaar


Ben's electronics voor (hobby) elektronica en Arduino producten. Wij hebben een ruime keuze in Arduino boards, bedrading, componenten, sensoren etc...




www.benselectronics.nl





But it burned through within 5 minutes. I've now got a 200A controller but that one was dead upon arrival unfortunately.


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## remy_martian (Feb 4, 2019)

Your driven sprocket looks way too small, which will stall the motor, burning up the controller.


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## GijsB (10 mo ago)

remy_martian said:


> Your driven sprocket looks way too small, which will stall the motor, burning up the controller.


Thanks Remy, 

Withd drive sprocket, you mean the one connected to the axle? The Buggy drives when I connect the motor directly to the battery.... But i guess it wouldn't hurt to replace that one with a bigger sprocket


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## remy_martian (Feb 4, 2019)

Drive sprocket -> the one on the motor

Driven sprocket -> the one on the axle

Go as big on the driven as you dare, while maintaining an inch or two of ground clearance. Somewhere near the rim diameter is good as a starting point.

On the drive side, a small sprocket is in order. Telling us your tooth counts helps, or at least not hiding it in the photo


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## GijsB (10 mo ago)

remy_martian said:


> Drive sprocket -> the one on the motor
> 
> Driven sprocket -> the one on the axle
> 
> ...


Thank you for your help!

The driven sprocket being small makes sense, had not thought about it.
I have contacted a go-kart shop for a new set of 219 sprockets.
Currently the drive sprocket has 13 tooth
The driven sprocket has 30

Below are some more photos


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## brian_ (Feb 7, 2017)

GijsB said:


> Currently the drive sprocket has 13 tooth
> The driven sprocket has 30


The chain drive reduction ratio is 30:13 or 2.3:1, so the motor is turning 2.3 times as fast as the tires. With more reduction the torque needed to accelerate the buggy means less torque from the motor, and so less current through the motor; more reduction ratio means more torque multiplication and therefore better acceleration and hill-climbing ability. On the other hand, with too much reduction the buggy's speed will be limited by how fast the motor can turn. As with all design choices, the reduction ratio is a compromise.

The motor can safely turn over 5400 RPM, as far as mechanical factors are concerned, but enough voltage must be provided to make it turn. The placard indicates that the motor can run up to 1800 RPM on 12 volts, but can't produce any power up at that speed, so at top road speed the motor should be turning more slowly than that.

The tires are marked for a maximum speed of 30 km/h, but I can't see the size, which determines how axle speed relates to road speed. What size are the tires, and what is the intended maximum road speed? At 12 years old, the driver should be able to handle a higher speed than those tires can, and a higher speed than that buggy is suitable for.

You may end up selecting a reduction ratio which gives good low-speed performance but a low top speed, then as floydr suggested adding battery voltage later to increase the top speed while maintaining the low-speed acceleration... if you choose a controller which can handle the higher voltage.


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## GijsB (10 mo ago)

brian_ said:


> The chain drive reduction ratio is 30:13 or 2.3:1, so the motor is turning 2.3 times as fast as the tires. With more reduction the torque needed to accelerate the buggy means less torque from the motor, and so less current through the motor; more reduction ratio means more torque multiplication and therefore better acceleration and hill-climbing ability. On the other hand, with too much reduction the buggy's speed will be limited by how fast the motor can turn. As with all design choices, the reduction ratio is a compromise.
> 
> The motor can safely turn over 5400 RPM, as far as mechanical factors are concerned, but enough voltage must be provided to make it turn. The placard indicates that the motor can run up to 1800 RPM on 12 volts, but can't produce any power up at that speed, so at top road speed the motor should be turning more slowly than that.
> 
> ...


Thanks Floyd!

My nephew isn't the bravest lol, so I'll start low but am happy that i can make the buggy go faster.
The tires are approximately 40cm in diameter.

But as recommended earlier, i will probably change out the sprockets to get a larger one on the axle.

RPM controller wise... I've got a 12V 100a battery... Maybe will double that to a 24V 100Ah battery..
Are the cheaper controllers still okay for that?

I currently have this one:


https://m.nl.aliexpress.com/item/4000091732150.html?gatewayAdapt=gloPc2nldMsite&spm=a2g0s.12269583.0.0.4d1e2a7d2SAyWx


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## brian_ (Feb 7, 2017)

GijsB said:


> The tires are approximately 40cm in diameter.


40 cm diameter means 126 cm circumference, so for instance 30 km/h (the tire limit) would be about 400 RPM at the axle. With the current sprockets, that's about 916 RPM for the motor; you could go for more reduction ratio, but if you doubled the ratio the motor wouldn't quite reach the corresponding speed even with no load (tires held off the ground). The lower you're willing to limit the top speed, the more reduction ratio you can use.


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## GijsB (10 mo ago)

brian_ said:


> 40 cm diameter means 126 cm circumference, so for instance 30 km/h (the tire limit) would be about 400 RPM at the axle. With the current sprockets, that's about 916 RPM for the motor; you could go for more reduction ratio, but if you doubled the ratio the motor wouldn't quite reach the corresponding speed even with no load (tires held off the ground). The lower you're willing to limit the top speed, the more reduction ratio you can use.


Thank you Brian, I'll keep that in mind with selecting the sprockets


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